SDI and MDI Fundamentals

Introduction

A single-document interface, SDI, is an application primarily made of a form equipped with a menu. An example is Notepad:

In some cases, an SDI can also have a toolbar and/or a status bar. Here is an example from Microsoft Works Spreadsheet:

All these features are left to the programmer to add and configure.

Although Notepad is text-based, an SDI can be any type of application: text, graphics, spreadsheet, anything. Therefore, to create an SDI, start from a normal form, add a menu to it, and configure it to do what you want.

To create a document using an SDI, the user launches the application. The SDI then presents a rectangular window with one frame and the inside is the document the user will use. In most cases, the application itself creates the document. The user can work on it and do whatever the application allows. To create another document of the same type, the user must open another instance of the application.

Practical Learning: Introducing MDI Applications

1. Start Microsoft Visual Studio
2. Create a Windows Forms App named StellarWaterPoint1
3. To create a form, on the main menu, click Project -> Add Form (Windows Forms)...
4. In the middle list, click About Box (Windows Forms)
5. Change the file Name to AboutSWP
6. Click Add
7. In the Solution Explorer, right-click StellarWaterPoint1 -> Add -> New Folder
8. Type Models as the name of the folder
9. To create a class, in the Solution Explorer, right-click Models -> Add -> Class...
10. On the main menu, click Project -> Add Class...
11. Replace the name with WaterMeter
12. Click Add
13. Change the code as follows:

    namespace StellarWaterPoint1.Models
    {
        internal readonly record struct WaterMeter
        {
            public readonly string? MeterNumber { get; init; }
            public readonly string? Make        { get; init; }
            public readonly string? Model       { get; init; }
            public readonly string? MeterSize   { get; init; }
        }
    }

14. To create another class, in the Solution Explorer, right-click Models -> Add -> Class...
15. On the main menu, click Project -> Add Class...
16. Replace the name with Customer
17. Click Add
18. Change the code as follows:

    namespace StellarWaterPoint1.Models
    {
        internal readonly record struct Customer
        {
            public readonly string? AccountNumber { get; init; }
            public readonly string? MeterNumber   { get; init; }
            public readonly string? FirstName     { get; init; }
            public readonly string? LastName      { get; init; }
            public readonly string? Address       { get; init; }
            public readonly string? City          { get; init; }
            public readonly string? County        { get; init; }
            public readonly string? State         { get; init; }
            public readonly string? ZIPCode       { get; init; }
        }
    }

19. To create another class, in the Solution Explorer, right-click Models -> Add -> Class...
20. On the main menu, click Project -> Add Class...
21. Replace the name with WaterBill
22. Click Add
23. Change the code as follows:

    namespace StellarWaterPoint1.Models
    {
        internal readonly record struct WaterBill
        {
            public readonly int     BillNumber            { get; init; }
            public readonly string? AccountNumber         { get; init; }
            public readonly string? MeterReadingStartDate { get; init; }
            public readonly string? MeterReadingEndDate   { get; init; }
            public readonly int     BillingDays           { get; init; }
            public readonly double  CounterReadingStart   { get; init; }
            public readonly double  CounterReadingEnd     { get; init; }
            public readonly double  TotalGallons          { get; init; }
            public readonly double  TotalCCF              { get; init; }
            public readonly double  FirstTierConsumption  { get; init; }
            public readonly double  SecondTierConsumption { get; init; }
            public readonly double  LastTierConsumption   { get; init; }
            public readonly double  WaterCharges          { get; init; }
            public readonly double  SewerCharges          { get; init; }
            public readonly double  EnvironmentCharges    { get; init; }
            public readonly double  TotalCharges          { get; init; }
            public readonly double  LocalTaxes            { get; init; }
            public readonly double  StateTaxes            { get; init; }
            public readonly double  AmountDue             { get; init; }
            public readonly string? PaymentDueDate        { get; init; }
            public readonly double  LateAmountDue         { get; init; }
            public readonly string? LatePaymentDueDate    { get; init; }
        }
    }

24. To create another class, in the Solution Explorer, right-click Models -> Add -> Class...
25. On the main menu, click Project -> Add Class...
26. Replace the name with Repository
27. Click Add
28. Change the code as follows:

    namespace StellarWaterPoint1.Models
    {
        sealed internal class Repository
        {
            public static Customer[]   Customers   { get; set; }
            public static WaterBill[]  WaterBills  { get; set; }
            public static WaterMeter[] WaterMeters { get; set; }
    
            static Repository()
            {
                Customers   = new Customer[10];
                WaterBills  = new WaterBill[10];
                WaterMeters = new WaterMeter[10];
            }
    
            public static void Add(in object addition)
            {
                if (addition is WaterMeter meter)
                {
                    for (int i = 0; i < WaterMeters.Length; i++)
                    {
                        if (string.IsNullOrEmpty(WaterMeters[i].MeterNumber))
                        {
                            WaterMeters[i]  = new WaterMeter()
                            {
                                MeterNumber = meter.MeterNumber,
                                Make        = meter.Make,
                                Model       = meter.Model,
                                MeterSize   = meter.MeterSize
                            };
                            break;
                        }
                    }
                }
                else if (addition is Customer client)
                {
                    for (int i = 0; i < Customers.Length; i++)
                    {
                        if (string.IsNullOrEmpty(Customers[i].AccountNumber))
                        {
                            Customers[i]      = new Customer()
                            {
                                AccountNumber = client.AccountNumber,
                                MeterNumber   = client.MeterNumber,
                                FirstName     = client.FirstName,
                                LastName      = client.LastName,
                                Address       = client.Address,
                                City          = client.City,
                                County        = client.County,
                                State         = client.State,
                                ZIPCode       = client.ZIPCode,
                            };
                            break;
                        }
                    }
                }
                else if (addition is WaterBill pay)
                {
                    for (int i = 0; i < WaterBills.Length; i++)
                    {
                        if (WaterBills[i].BillNumber == 0)
                        {
                            WaterBills[i]             = new WaterBill()
                            {
                                BillNumber            = pay.BillNumber,
                                AccountNumber         = pay.AccountNumber,
                                MeterReadingStartDate = pay.MeterReadingStartDate,
                                MeterReadingEndDate   = pay.MeterReadingEndDate,
                                BillingDays           = pay.BillingDays,
                                CounterReadingStart   = pay.CounterReadingStart,
                                CounterReadingEnd     = pay.CounterReadingEnd,
                                TotalGallons          = pay.TotalGallons,
                                TotalCCF              = pay.TotalCCF,
                                FirstTierConsumption  = pay.FirstTierConsumption,
                                SecondTierConsumption = pay.SecondTierConsumption,
                                LastTierConsumption   = pay.LastTierConsumption,
                                WaterCharges          = pay.WaterCharges,
                                SewerCharges          = pay.SewerCharges,
                                EnvironmentCharges    = pay.EnvironmentCharges,
                                TotalCharges          = pay.TotalCharges,
                                LocalTaxes            = pay.LocalTaxes,
                                StateTaxes            = pay.StateTaxes,
                                AmountDue             = pay.AmountDue,
                                PaymentDueDate        = pay.PaymentDueDate,
                                LateAmountDue         = pay.LateAmountDue,
                                LatePaymentDueDate    = pay.LatePaymentDueDate
                            };
                            break;
                        }
                    }
                }
            }
    
            public static WaterMeter GetWaterMeter(in string number)
            {
                if (number is not null)
                {
                    for (int i = 0; i < WaterMeters.Length; i++)
                    {
                        if (WaterMeters[i].MeterNumber!.Equals(number))
                        {
                            return WaterMeters[i];
                        }
                    }
                }
    
                return new WaterMeter();
            }
    
            public static Customer GetCustomer(in string number)
            {
                if (number is null)
                    return new Customer();
    
                for (int i = 0; i < Customers.Length; i++)
                {
                    if (Customers[i].AccountNumber!.Equals(number))
                    {
                        return Customers[i];
                    }
                }
    
                return new Customer();
            }
    
            public static WaterBill GetWaterBill(in int number)
            {
                if (number == 0)
                    return new WaterBill();
    
                for (int i = 0; i < WaterBills.Length; i++)
                {
                    if (WaterBills[i].BillNumber == number)
                    {
                        return WaterBills[i];
                    }
                }
    
                return new WaterBill();
            }
        }
    }

MDI Fundamentals

A multiple-document interface, MDI, is an application that primarily has a form and a menu. Some, if not most, MDIs also have one or more toolbars and/or a status bar. Here is an example:

Like a normal application, to use an MDI, the user must launch it. In some cases, when the application starts, it is empty; that is, no document is created and the title bar displays a caption, usually the name of the application. Usually, there are steps the user must follow to create a document. In some other cases, when the application is launched, it automatically creates a document. A document resides inside the parent frame of the application. That is, a child document can use only the area reserved for it. The child document has its own system icon, its own title bar, and its own system buttons (Minimize, Maximize/Restore, and Close).

To use the whole area, the user can maximize the child document. When this is done, the child merges its title bar with the parent's. The new caption of the title bar becomes made of the text of the parent, followed by -, and followed by the caption the child window was using. The system buttons of the child document display under those of the parent frame:

Once a document has been created, the user can use it. Normally, the application must give the user the ability to create other documents while still using the application. If many documents have been created, all of them are confined to the frame of the parent:

The user can maximize the child forms. If so, the document that was in front occupies the whole area devoted to child documents. The other child forms stay in the back but become invisible.

One of the differences between an SDI and an MDI is that, because the child document and the MDI application don't share a frame, the user can close the child document and keep the application open.

Creating an MDI Application

As mentioned already, there is nothing magical with creating an SDI application. You start with a form, add a menu to it, and specify what the application should allow a user to do with a document. As we will see, an MDI requires more steps.

You start an MDI application with a normal form. You can create a Windows Forms Application using Microsoft Visual Studio or derive a class from Form. Here is an example:

using System.Windows.Forms;

public class CommonParent : Form
{
    public CommonParent()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        
    }

    [STAThread]
    public static int Main()
    {
        Application.Run(new CommonParent());

        return 0;
    }
}

The primary form of an MDI application is referred to as the parent or MDI container. It provides the frame inside of which the documents will reside. To provide this functionality, the Form class is equipped with a Boolean property named IsMdiContainer. Therefore, after creating the first form of your application, to indicate that it acts as the main frame, set this property to true. You can do this in the Properties window if you are visually creating your application, or programmatically. Here is an example:

using System.Windows.Forms;

public class CommonParent : Form
{
    public CommonParent()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        this.IsMdiContainer = true;
    }

    [STAThread]
    public static int Main()
    {
        Application.Run(new CommonParent());

        return 0;
    }
}

This would produce:

The primary characteristic of an MDI is that it contains other forms. These forms must be created and made available to the parent. Each form can be created using a predefined form or you can programmatically create one by declaring an object of type Form. To allow you to specify that a form has a parent and will act as a child, the Form class is equipped with a property named MdiParent. This is a read-write property. The set accessor indicates what form acts as this one's parent. To provide this information, assign the main form this form's MdiParent. After doing this, you can display the form when you are ready, by calling its Show() method. Here is an example:

using System.Windows.Forms;

public class CommonParent : Form
{
    public CommonParent()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        this.IsMdiContainer = true;

        Form frmChild = new Form();
        frmChild.MdiParent = this;

        frmChild.Show();
    }

    [STAThread]
    public static int Main()
    {
        Application.Run(new CommonParent());

        return 0;
    }
}

This would produce:

Practical Learning: Creating an MDI Application

1. In the Solution Explorer, right-click Form1.cs and click Rename
2. Change the name to WaterDistribution.cs
3. Press Enter three times to apply the name and display the form
4. In the Properties window, change the following characteristics:
   IsMdiContainer: True
   StartPosition: CenterScreen
   Text: Stellar Water Point
5. In the Solution Explorer, right-click StellarWaterPoint1 -> Add -> New Folder
6. Type WaterMeters as the name of the folder
7. To create a form, in the Solution Explorer, right-click WaterMeters -> Add -> Form(Windows Forms)...
8. Type Create
9. Press Enter
10. Design the form as follows:

    

    Control		(Name)	Text	Other Properties
    Label			&Meter #:
    MaskedTextBox		mtbMeterNumber		Masked: 000-00-000
    Label			M&ake:
    TextBox		txtMake
    Label			M&odel:
    TextBox		txtModel		Modifiers: Public
    Label			Me&ter Size:
    TextBox		txtMeterSize
    Button		btnSaveWateMeter	S&ave Water Meter

11. To create a form, in the Solution Explorer, right-click WaterMeters -> Add -> Form(Windows Forms)...
12. Type Manage
13. Press Enter
14. In the Toolbox, click the ListView button and click the form
15. On the form, right-click the list view and click Edit Columns...
16. Create the columns as follows:

    (Name)	Text	Width
    colWaterMeterId	Id	40
    colMeterNumber	Meter #	150
    colMake	Make	225
    colModel	Model	100
    colMeterSize	Meter Size	150

17. Click OK
18. Complete the design of the form as follows:

    

    Control		(Name)	Other Properties
    ListView		lvwWaterMeters	FullRowSelect: True GridLines: True View: Details Anchor: Top, Bottom, Left, Right

19. In the Solution Explorer, right-click StellarWaterPoint1 -> Add -> New Folder
20. Type Customers as the name of the folder
21. To create a form, on the main menu, click Customers -> Add Form (Windows Forms)...
22. Type Create as the name of the file
23. Click Add
24. Design the form as follows:

    

    Control		(Name)	Text	Mask
    Label			&Account #:
    MaskedTextBox		mtbAccountNumber		Masked: 0000-000-0000
    Label			&Meter #:
    MaskedTextBox		mtbMeterNumber		Masked: 000-00-000
    Button		btnFindWaterMeter	&Find Water Meter
    Label			Meter &Details:
    TextBox		txtMeterDetails
    Label			&First Name:
    TextBox		txtFirstName
    Label			&Last Name:
    TextBox		txtLastName
    Label			&Address:
    TextBox		txtAddress
    Label			C&ity:
    TextBox		txtCity
    Label			C&ounty:
    TextBox		txtCounty
    Label			&State:
    TextBox		txtState
    Label			&ZIP-Code:
    MaskedTextBox		mtbZIPCode		Masked: Zip-Code
    Button		btnSaveCustomerAccount	S&ave Customer Account

25. To create a form, in the Solution Explorer, right-click Models -> Add -> Form(Windows Forms)...
26. Type ViewAll
27. Press Enter
28. In the Toolbox, click the ListView button and click the form
29. On the form, right-click the list view and click Edit Columns...
30. Create the columns as follows:

    (Name)	Text	TextAlign	Width
    colCustomerId	Id		40
    colAccountNumber	Account #	Center	175
    colMeterNumber	Meter #	Center	150
    colFirstName	First Name		125
    colLastName	Last Name		125
    colAddress	Address		250
    colCity	City		125
    colCounty	County		150
    colState	State	Center
    colZIPCode	ZIP-Code	Center	125

31. Click OK
32. Complete the design of the form as follows:

    

    Control		(Name)	Other Properties
    ListView		lvwCustomers	FullRowSelect: True GridLines: True View: Details Anchor: Top, Bottom, Left, Right

33. In the Solution Explorer, right-click StellarWaterPoint1 -> Add -> New Folder
34. Type WaterBills as the name of the folder
35. To create a form, in the Solution Explorer, right-click WaterBills -> Add -> Form (Windows Forms)...
36. Type Create as the name of the file
37. Press Enter
38. Design the form as follows:

    

    Control		(Name)	Text	Other Properties
    Label			Water Bill #:
    TextBox		txtBillNumber
    GroupBox			Customer Information
    Label			Account #:
    MaskedTextBox		mtbAccountNumber		Masked: 0000-000-0000
    Button		btnFindCustomerAccount	Find Customer Account
    Label			Customer Name:
    TextBox		txtCustomerName
    Label			Address:
    TextBox		txtAddress
    TextBox		txtCity
    TextBox		txtCounty
    TextBox		txtState
    MaskedTextBox		mtbZIPCode		Masked: Zip-Code
    Label			_______________________
    Label			Meter Details:
    TextBox		txtMeterDetails	Modifiers: Public
    GroupBox			Meter Reading
    Label			Meter Reading Start Date:
    MaskedTextBox		mtbMeterReadingStartDate		Masked: Short Date
    Label			Meter Reading End Date:
    MaskedTextBox		mtbMeterReadingEndDate		Masked: Short Date
    Label			Counter Reading Start:
    TextBox		txtCounterReadingStart
    Label			Counter Reading End:
    TextBox		txtCounterReadingEnd
    Button		btnEvaluateWaterBill	Evaluate Water Bill
    GroupBox			Meter Result
    Label			Billing Days:
    TextBox		txtBillingDays		TextAlign: Right
    Label			Total Gallons:
    TextBox		txtTotalGallons		TextAlign: Right
    Label			Total CCF:
    TextBox		txtTotalCCF		TextAlign: Right
    Label			First Tier Consumption:
    TextBox		txtFirstTierConsumption		TextAlign: Right
    Label			Second Tier:
    TextBox		txtSecondTierConsumption		TextAlign: Right
    Label			Last Tier:
    TextBox		txtLastTierConsumption		TextAlign: Right
    GroupBox			Consumption Charges
    Label			Water Charges:
    TextBox		txtWaterCharges		TextAlign: Right
    Label			Sewer Charges:
    TextBox		txtSewerCharges		TextAlign: Right
    Label			Environment Charges:
    TextBox		txtEnvironmentCharges		TextAlign: Right
    Label			Total Charges:
    TextBox		txtTotalCharges		TextAlign: Right
    GroupBox			Taxes
    Label			Local Taxes:
    TextBox		txtLocalTaxes		TextAlign: Right
    Label			State Taxes:
    TextBox		txtStateTaxes		TextAlign: Right
    GroupBox			Water Bill Payment
    Label			Payment Due Date:
    MaskedTextBox		mtbPaymentDueDate		Masked: Short Date
    Label			Amount Due:
    TextBox		txtAmountDue		TextAlign: Right
    Label			Late Payment Due Date:
    MaskedTextBox		mtbLatePaymentDueDate		Masked: Short Date
    Label			Late Amount Due:
    TextBox		txtLateAmountDue		TextAlign: Right
    Button		btnSaveWaterBill	Save Water Bill

39. To create a new form, on the main menu, click Project and click Form (Windows Forms)...
40. Type Details as the name of the form
41. Click Add
42. Make that form the same size as the New Water Bill form
43. Select everything on the New Water Bill form. Copy that selection and paste it in the new WaterBillView form
44. On the WaterBillView form, delete the Find Customer Account, the Evaluate Water Bill, and the Save Water Bill buttons
45. Add a Find Water Bill button as follows:

    

    Control		(Name)	Text
    Button		btnFindWaterBill	Find Water &Bill

MDI Characteristics

Introduction to the Children of an MDI

When you create an MDI application, you must make sure you provide your users with the ability to create documents. In fact, probably one of your first assignments is to make sure the user can create as many documents as necessary. As the documents are created, you need a way to programmatically keep track of the child forms. For example, you can store the documents in a collection. To assist you with this, the Form class is equipped with a property named MdiChildren, which is a read-only array. Each element of the MdiChildren[] array is of type Form. Therefore, to access a child form of an MDI application, you can pass an index to this property.

The Layout of Child Forms

Based on the standards defined in the operating system, as child forms are created in an MDI application, they are positioned each on top of the previous one but below the next one. The arrangement uses a 3-D coordiniate system whose origin is on the lower-left corner of the parent's frame just under the title bar (or the menu, if any; or the toolbar, if any), with the Z axis moving from the monitor towards you:

The operating system allows the user to choose among different arrangements. For example, you can position the documents as vertical columns, as horizontal rows, or as tiles. To support this, the Form class is equipped with a method named LayoutMdi. Its syntax is:

public void LayoutMdi(MdiLayout value);

The LayoutMdi() method takes an argument that is a member of the MdiLayout enumeration. The members of this enumeration are Cascade, TileHorizontal, TileVertical, and ArrangeIcons.

Practical Learning: Laying Out the Documents

1. In the Solution Explorer, double-click WaterDistribution.cs to display the main form of the application
2. In the Toolbox, expand Menus & Toolbars
3. In the Menus & Toolbars section of the Toolbox, click MenuStrip and click the form
4. In the Properties window, click (Name) and type msMainMenu
5. Still in the Properties window, click Items and click its button
6. Using the Add button, create three items as follows:

   Text	(Name)
   &File	miFile
   Water &Bills	miWaterBills
   &Customers	miCustomers
   Water &Meters	miWaterMeters
   &Window	miWindow
   &Help	miHelp

7. In the Members list of the Items Collection Editor, click miFile
8. In the right list, click DropDownItems and click its button
9. Using the Add button, create two items as follows:

   Text	(Name)	Shortcuts
   E&xit	miFileExit	Alt + F4

10. On the Items Collection Editor (miFile.DropDownItems) dialog box, click OK
11. In the Members list of the Items Collection Editor, click miWaterBills
12. In the right list, click DropDownItems and click its button
13. Using the Add button, create two items as follows:

    Text	(Name)	Shortcuts
    &Prepare Water Bill...	miWaterBillsCreate	Ctrl+Shift+B
    &View Water Bill...	miWaterBillsView	Ctrl+Shift+V

14. On the Items Collection Editor (miWaterBills.DropDownItems) dialog box, click OK
15. In the Members list of the Items Collection Editor, click miCustomers
16. In the right list, click DropDownItems and click its button
17. Using the Add button, create two items as follows:

    Text	(Name)	Shortcuts
    &Create Customer Account...	miCustomersCreate	Ctrl+Shift+C
    &View All Accounts...	miCustomerViewAll	Ctrl+Shift+A

18. On the Items Collection Editor (miCustomers.DropDownItems) dialog box, click OK
19. In the Members list of the Items Collection Editor, click miWaterMeters
20. In the right list, click DropDownItems and click its button
21. Using the Add button, create two items as follows:

    Text	(Name)	Shortcuts
    &Setup Water Meter...	miWaterMetersCreate	Ctrl+Shift+W
    &View All Water Meters...	miWaterMeterViewAll	Ctrl+Shift+T

22. On the Items Collection Editor (miWaterMeters.DropDownItems) dialog box, click OK
23. In the Members list of the Items Collection Editor, click miWindow
24. In the right list, click DropDownItems and click its button
25. Using the Add button, create two items as follows:

    Text	(Name)
    &Arrange	miWindowArrange
    &Cascade	miWindowCascade
    Tile &Horizontal	miWindowTileHorizontal
    Tile &Vertical	mnuWindowTileVertical

26. On the Items Collection Editor (miWindow.DropDownItems) dialog box, click OK
27. In the Members list of the Items Collection Editor, click miHelp
28. In the right list, click DropDownItems and click its button
29. Using the Add button, create an item as follows:

    Text	(Name)	Shortcuts
    &About Stellar Water Point...	miHelpAbout	Ctrl+F1

30. On the Items Collection Editor (miHelp.DropDownItems) dialog box, click OK
31. On the Items Collection Editor dialog box, click OK
32. On the Stellar Water Point form, click the Water Bills menu item and double-click Prepare Water Bill...
33. Return to the Stellar Water Point form
34. On the Stellar Water Point form, below Prepare Water Bill..., double-click View Water Bill...
35. Return to the Stellar Water Point form
36. Click the Customers menu item and double-click Create Customer Account...
37. Return to the Stellar Water Point form and, below Create Customer Account..., double-click View All Accounts
38. Return to the Stellar Water Point form
39. Click the Water Meters menu item and double-click Setup Water Meter...
40. Return to the Stellar Water Point form and, below Setup Water Meter..., double-click View All Water Meters...
41. Return to the Stellar Water Point form
42. Click the Window menu item and double-click Arrange
43. Return to the Stellar Water Point form and, below Arrange, double-click Cascade
44. Return to the Stellar Water Point form and, below Cascade, double-click Tile Horizontal
45. Return to the Stellar Water Point form and, below Tile Horizontal, double-click Tile Vertical
46. Return to the Stellar Water Point form
47. Click the Help menu item and double-click About Stellar Water Point...
48. Return to the Stellar Water Point form
49. Click the File menu item and double-click Exit
50. Change the document as follows:

    namespace StellarWaterPoint11
    {
        public partial class WaterDistribution : Form
        {
            public static bool MetersDisplaying;
            public static bool CreateMeterDisplaying;
    
            public static bool ClientsDisplaying;
            public static bool CreateClientDisplaying;
    
            public static bool ViewBillDisplaying;
            public static bool CreateBillDisplaying;
    
            private WaterMeters.Create createMeter;
            private WaterMeters.Manage meters;
    
            private Customers.Create client;
            private Customers.ViewAll clients;
    
            private WaterBills.Create createBill;
            private WaterBills.Details billDetails;
    
            public WaterDistribution()
            {
                InitializeComponent();
    
                MetersDisplaying = false;
                CreateMeterDisplaying = false;
    
                ClientsDisplaying = false;
                CreateClientDisplaying = false;
    
                ViewBillDisplaying = false;
                CreateBillDisplaying = false;
    
                createBill = new WaterBills.Create();
                billDetails = new WaterBills.Details();
    
                createMeter = new WaterMeters.Create();
                meters = new WaterMeters.Manage();
    
                client = new Customers.Create();
                clients = new Customers.ViewAll();
            }
    
            private void miWaterBillsCreate_Click(object sender, EventArgs e)
            {
                if (CreateBillDisplaying == false)
                {
                    createBill = new();
                    createBill.MdiParent = this;
                    createBill.Show();
    
                    CreateBillDisplaying = true;
                }
                else
                {
                    createBill.BringToFront();
                }
            }
    
            private void miWaterBillsView_Click(object sender, EventArgs e)
            {
                if (ViewBillDisplaying == false)
                {
                    billDetails = new();
    
                    billDetails.MdiParent = this;
                    billDetails.Show();
                }
                else
                {
                    billDetails.BringToFront();
                }
            }
    
            private void miCustomersCreate_Click(object sender, EventArgs e)
            {
                if (CreateClientDisplaying == false)
                {
                    client = new Customers.Create();
                    client.MdiParent = this;
                    client.Show();
    
                    CreateClientDisplaying = true;
                }
                else
                {
                    client.BringToFront();
                }
            }
    
            private void miCustomerViewAll_Click(object sender, EventArgs e)
            {
                if (ClientsDisplaying == false)
                {
                    clients = new();
                    clients.MdiParent = this;
                    clients.Show();
    
                    ClientsDisplaying = true;
                }
                else
                {
                    clients.BringToFront();
                }
            }
    
            private void miWaterMetersCreate_Click(object sender, EventArgs e)
            {
                if (CreateMeterDisplaying == false)
                {
                    createMeter = new();
                    createMeter.MdiParent = this;
                    createMeter.Show();
    
                    CreateMeterDisplaying = true;
                }
                else
                {
                    createMeter.BringToFront();
                }
            }
    
            private void miWaterMeterViewAll_Click(object sender, EventArgs e)
            {
                if (MetersDisplaying == false)
                {
                    meters = new WaterMeters.Manage();
    
                    meters.MdiParent = this;
                    meters.Show();
    
                    MetersDisplaying = true;
                }
                else
                {
                    meters.BringToFront();
                }
            }
    
            private void miWindowArrange_Click(object sender, EventArgs e)
            {
                LayoutMdi(MdiLayout.ArrangeIcons);
            }
    
            private void miWindowCascade_Click(object sender, EventArgs e)
            {
                LayoutMdi(MdiLayout.Cascade);
            }
    
            private void miWindowTileHorizontal_Click(object sender, EventArgs e)
            {
                LayoutMdi(MdiLayout.TileHorizontal);
            }
    
            private void mnuWindowTileVertical_Click(object sender, EventArgs e)
            {
                LayoutMdi(MdiLayout.TileVertical);
            }
    
            private void miHelpAbout_Click(object sender, EventArgs e)
            {
                AboutSWP about = new AboutSWP();
                about.ShowDialog();
            }
    
            private void miFileExit_Click(object sender, EventArgs e)
            {
                Close();
            }
        }
    }

51. In the Solution Explorer, below Customers, double-click Create
52. On the Customers Create form, double-click the Find Water Meter button
53. Return to the Customers Create form and double-click the Save Customer Account button
54. Return to the Customers Create form and click an unoccupied area of the form
55. In the Solution Explorer, click the Events button
56. While the Customers Create form is selected, in the Events section of the Properties window, double-click Activated
57. Return to the Customers Create form and, in the Events section of the Properties window, double-click FormClosing
58. Implement the events as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.Customers
    {
        public partial class Create : Form
        {
            public Create()
            {
                InitializeComponent();
            }
    
            private void btnFindWaterMeter_Click(object sender, EventArgs e)
            {
                if (string.IsNullOrEmpty(mtbMeterNumber.Text))
                {
                    MessageBox.Show("You must type the meter number associated with the customer's account.",
                                    "Stellar Water Point", MessageBoxButtons.OK);
                    return;
                }
    
                WaterMeter meter = Repository.GetWaterMeter(mtbMeterNumber.Text);
    
                txtMeterDetails.Text = meter.Make    + " " +
                                       meter.Model   +
                                       " (Meter #: " + meter.MeterSize + ")";
            }
    
            private void btnSaveCustomerAccount_Click(object sender, EventArgs e)
            {
                if (string.IsNullOrEmpty(mtbAccountNumber.Text))
                {
                    MessageBox.Show("You must type an account number for the new customer.",
                                    "Stellar Water Point", MessageBoxButtons.OK);
                    return;
                }
    
                Customer account = new Customer()
                {
                    AccountNumber = mtbAccountNumber.Text,
                    MeterNumber   = mtbMeterNumber.Text,
                    FirstName     = txtFirstName.Text,
                    LastName      = txtLastName.Text,
                    Address       = txtAddress.Text,
                    City          = txtCity.Text,
                    County        = txtCounty.Text,
                    State         = txtState.Text,
                    ZIPCode       = mtbZIPCode.Text
                };
    
                Repository.Add(account);
                Close();
            }
    
            private void Create_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.CreateClientDisplaying == true)
                {
                    WaterDistribution.CreateClientDisplaying = false;
                    Close();
                }
            }
        }
    }

59. In the Solution Explorer, below Customers, double-click ViewAll
60. Click an unoccupied area of the form
61. In the Events section of the Properties window, double-click Activated
62. Return to the form and, in the Events section of the Properties window, double-click FormClosing
63. Change the document as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.Customers
    {
        public partial class ViewAll : Form
        {
            public ViewAll()
            {
                InitializeComponent();
            }
    
            private void ShowCustomers()
            {
                int counter = 1;
    
                lvwCustomers.Items.Clear();
    
                foreach (Customer cust in Repository.Customers)
                {
                    if (!(string.IsNullOrEmpty(cust.AccountNumber)))
                    {
                        ListViewItem lviCustomer = new ListViewItem(counter++.ToString());
    
                        lviCustomer.SubItems.Add(cust.AccountNumber);
                        lviCustomer.SubItems.Add(cust.MeterNumber);
                        lviCustomer.SubItems.Add(cust.FirstName);
                        lviCustomer.SubItems.Add(cust.LastName);
                        lviCustomer.SubItems.Add(cust.Address);
                        lviCustomer.SubItems.Add(cust.City);
                        lviCustomer.SubItems.Add(cust.County);
                        lviCustomer.SubItems.Add(cust.State);
                        lviCustomer.SubItems.Add(cust.ZIPCode);
    
                        lvwCustomers.Items.Add(lviCustomer);
                    }
                }
            }
    
            private void ViewAll_Activated(object sender, EventArgs e)
            {
                ShowCustomers();
            }
    
            private void ViewAll_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.ClientsDisplaying == true)
                {
                    WaterDistribution.ClientsDisplaying = false;
                    Close();
                }
            }
        }
    }

64. In the Solution Explorer, below WaterMeters, double-click Create
65. On the Water Meters - Create form, double-click the S&ave Water Meter button
66. Return to the form and, in the Events section of the Properties window, double-click Activated
67. Return to the form and, in the Events section of the Properties window, double-click FormClosing
68. Implement the events as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.WaterMeters
    {
        public partial class Create : Form
        {
            public Create()
            {
                InitializeComponent();
            }
    
            private void btnSaveWaterMeter_Click(object sender, EventArgs e)
            {
                if (string.IsNullOrEmpty(mtbMeterNumber.Text))
                {
                    MessageBox.Show("You must type the meter number. " +
                                    "Otherwise, the water meter cannot be set up.",
                                    "Stellar Water Point", MessageBoxButtons.OK);
                    return;
                }
    
                WaterMeter wm = new WaterMeter()
                {
                    MeterNumber = mtbMeterNumber.Text,
                    Make = txtMake.Text,
                    Model = txtModel.Text,
                    MeterSize = txtMeterSize.Text
                };
    
                Repository.Add(wm);
                Close();
            }
    
            private void Create_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.CreateMeterDisplaying == true)
                {
                    WaterDistribution.CreateMeterDisplaying = false;
                    Close();
                }
            }
        }
    }

69. In the Solution Explorer, below WaterMeters, double-click Manage
70. In the Events section of the Properties window, double-click Activated
71. In the Events section of the Properties window, double-click FormClosing
72. Change the document as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.WaterMeters
    {
        public partial class Manage : Form
        {
            public Manage()
            {
                InitializeComponent();
            }
    
            void ShowWaterMeters()
            {
                int counter = 1;
    
                lvwWaterMeters.Items.Clear();
    
                foreach (WaterMeter wm in Repository.WaterMeters)
                {
                    if (!(string.IsNullOrEmpty(wm.MeterNumber)))
                    {
                        ListViewItem lviWaterMeter = new ListViewItem(counter++.ToString());
    
                        lviWaterMeter.SubItems.Add(wm.MeterNumber);
                        lviWaterMeter.SubItems.Add(wm.Make);
                        lviWaterMeter.SubItems.Add(wm.Model);
                        lviWaterMeter.SubItems.Add(wm.MeterSize);
    
                        lvwWaterMeters.Items.Add(lviWaterMeter);
                    }
                }
            }
    
            private void Manage_Activated(object sender, EventArgs e)
            {
                ShowWaterMeters();
            }
    
            private void Manage_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.MetersDisplaying == true)
                {
                    WaterDistribution.MetersDisplaying = false;
                    Close();
                }
            }
        }
    }

73. In the Solution Explorer, below WaterBills, double-click Create
74. On the Water Bills - Create form, double-click the Find Customer Account button
75. Return to the Water Bills - Create form and double-click the Evaluate Water Bill button
76. Return to the Water Bills - Create form and double-click the Save Water Bill button
77. Return to the form and, in the Events section of the Properties window, double-click FormClosing
78. Change the document as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.WaterBills
    {
        public partial class Create : Form
        {
            public Create()
            {
                InitializeComponent();
            }
    
            private void btnFindCustomerAccount_Click(object sender, EventArgs e)
            {
                if (string.IsNullOrEmpty(mtbAccountNumber.Text))
                {
                    MessageBox.Show("You must enter a bill number.",
                                    "Stellar Water Point", MessageBoxButtons.OK);
                    return;
                }
    
                Customer client = Repository.GetCustomer(mtbAccountNumber.Text);
    
                string strMeterNumber = string.Empty;
    
                txtCustomerName.Text = client.FirstName + " " + client.LastName;
                strMeterNumber       = client.MeterNumber!;
                txtAddress.Text      = client.Address;
                txtCity.Text         = client.City;
                txtCounty.Text       = client.County;
                txtState.Text        = client.State;
                txtZIPCode.Text      = client.ZIPCode;
    
                WaterMeter meter     = Repository.GetWaterMeter(strMeterNumber);
    
                txtMeterDetails.Text = meter.Make    + " " +
                                       meter.Model   +
                                       " (Meter #: " + meter.MeterSize + ")";
            }
    
            private void btnEvaluateWaterBill_Click(object sender, EventArgs e)
            {
                double counterStart = 0, counterEnd = 0;
    
                try
                {
                    counterStart = double.Parse(txtCounterReadingStart.Text);
                }
                catch (FormatException feCRStart)
                {
                    MessageBox.Show("There was a problem with the value of the " +
                                    "Counter Reading Start. The error produced is: " + feCRStart.Message,
                                    "Stellar Water Point", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
    
                try
                {
                    counterEnd = double.Parse(txtCounterReadingEnd.Text);
                }
                catch (FormatException feCREnd)
                {
                    MessageBox.Show("There was a problem with the value of the " +
                                    "Counter Reading End. The error produced is: " + feCREnd.Message,
                                    "Stellar Water Point", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
    
                double consumption  = counterEnd   - counterStart;
                double gallons      = consumption  * 748.05;
                double firstTier    = gallons      * (48.00 / 10000.00);
                double secondTier   = gallons      * (32.00 / 10000.00);
                double lastTier     = gallons      * (20.00 / 10000.00);
                double waterCharges = firstTier    + secondTier + lastTier;
                double sewerCharges = waterCharges * 28.65 / 100;
                double envCharges   = waterCharges * 0.22184;
                double totalCharges = waterCharges + sewerCharges + envCharges;
                double localTaxes   = totalCharges * 0.06148;
                double stateTaxes   = totalCharges * 0.01374;
                double amtDue       = totalCharges + localTaxes + stateTaxes;
    
                txtTotalCCF.Text              = consumption.ToString();
                txtTotalGallons.Text          = gallons.ToString("F");
                txtFirstTierConsumption.Text  = firstTier.ToString("F");
                txtSecondTierConsumption.Text = secondTier.ToString("F");
                txtLastTierConsumption.Text   = lastTier.ToString("F");
                txtWaterCharges.Text          = waterCharges.ToString("F");
                txtSewerCharges.Text          = sewerCharges.ToString("F");
                txtEnvironmentCharges.Text    = envCharges.ToString("F");
                txtTotalCharges.Text          = totalCharges.ToString("F");
                txtLocalTaxes.Text            = localTaxes.ToString("F");
                txtStateTaxes.Text            = stateTaxes.ToString("F");
                txtAmountDue.Text             = amtDue.ToString("F");
                txtLateAmountDue.Text         = (amtDue + 8.95).ToString("F");
            }
    
            private void btnSaveWaterBill_Click(object sender, EventArgs e)
            {
                WaterBill bill = new WaterBill()
                {
                    BillNumber            = int.Parse(txtBillNumber.Text),
                    AccountNumber         = mtbAccountNumber.Text,
                    MeterReadingStartDate = mtbMeterReadingStartDate.Text,
                    MeterReadingEndDate   = mtbMeterReadingEndDate.Text,
                    BillingDays           = int.Parse(txtBillingDays.Text),
                    CounterReadingStart   = double.Parse(txtCounterReadingStart.Text),
                    CounterReadingEnd     = double.Parse(txtCounterReadingEnd.Text),
                    TotalGallons          = double.Parse(txtTotalGallons.Text),
                    TotalCCF              = double.Parse(txtTotalCCF.Text),
                    FirstTierConsumption  = double.Parse(txtFirstTierConsumption.Text),
                    SecondTierConsumption = double.Parse(txtSecondTierConsumption.Text),
                    LastTierConsumption   = double.Parse(txtLastTierConsumption.Text),
                    WaterCharges          = double.Parse(txtWaterCharges.Text),
                    SewerCharges          = double.Parse(txtSewerCharges.Text),
                    EnvironmentCharges    = double.Parse(txtEnvironmentCharges.Text),
                    TotalCharges          = double.Parse(txtTotalCharges.Text),
                    LocalTaxes            = double.Parse(txtLocalTaxes.Text),
                    StateTaxes            = double.Parse(txtStateTaxes.Text),
                    AmountDue             = double.Parse(txtAmountDue.Text),
                    PaymentDueDate        = mtbPaymentDueDate.Text,
                    LateAmountDue         = double.Parse(txtLateAmountDue.Text),
                    LatePaymentDueDate    = mtbLatePaymentDueDate.Text
                };
    
                Repository.Add(bill);
                Close();
            }
    
            private void Create_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.CreateBillDisplaying == true)
                {
                    WaterDistribution.CreateBillDisplaying = false;
                    Close();
                }
            }
        }
    }

79. In the Solution Explorer, below WaterBills, double-click Details
80. On the form, double-click the Find Water Bill button
81. Return to the Water Bills - Details form and, in the Events section of the Properties window, double-click FormClosing
82. Change the document as follows:

    using StellarWaterPoint1.Models;
    
    namespace StellarWaterPoint1.WaterBills
    {
        public partial class Details : Form
        {
            public Details()
            {
                InitializeComponent();
            }
    
            private void btnFindWaterBill_Click(object sender, EventArgs e)
            {
                if (string.IsNullOrEmpty(txtWaterBillNumber.Text))
                {
                    MessageBox.Show("You must type a water bill number.",
                                    "Stellar Water Point", MessageBoxButtons.OK);
                    return;
                }
    
                WaterBill bill = Repository.GetWaterBill(int.Parse(txtWaterBillNumber.Text));
    
                mtbAccountNumber.Text = bill.AccountNumber;
                mtbMeterReadingStartDate.Text = bill.MeterReadingStartDate;
                mtbMeterReadingEndDate.Text = bill.MeterReadingEndDate;
                txtBillingDays.Text = bill.BillingDays.ToString();
                txtCounterReadingStart.Text = bill.CounterReadingStart.ToString();
                txtCounterReadingEnd.Text = bill.CounterReadingEnd.ToString();
                txtTotalGallons.Text = bill.TotalGallons.ToString();
                txtTotalCCF.Text = bill.TotalCCF.ToString();
                txtFirstTierConsumption.Text = bill.FirstTierConsumption.ToString();
                txtSecondTierConsumption.Text = bill.SecondTierConsumption.ToString();
                txtLastTierConsumption.Text = bill.LastTierConsumption.ToString();
                txtWaterCharges.Text = bill.WaterCharges.ToString();
                txtSewerCharges.Text = bill.SewerCharges.ToString();
                txtEnvironmentCharges.Text = bill.EnvironmentCharges.ToString();
                txtTotalCharges.Text = bill.TotalCharges.ToString();
                txtLocalTaxes.Text = bill.LocalTaxes.ToString();
                txtStateTaxes.Text = bill.StateTaxes.ToString();
                txtAmountDue.Text = bill.AmountDue.ToString();
                mtbPaymentDueDate.Text = bill.PaymentDueDate;
                txtLateAmountDue.Text = bill.LateAmountDue.ToString();
                mtbLatePaymentDueDate.Text = bill.LatePaymentDueDate;
    
                string strMeterNumber = string.Empty;
                Customer client = Repository.GetCustomer(mtbAccountNumber.Text);
    
                strMeterNumber = client.MeterNumber!;
                txtCustomerName.Text = client.FirstName + " " + client.LastName;
                txtAddress.Text = client.Address;
                txtCity.Text = client.City;
                txtCounty.Text = client.County;
                txtState.Text = client.State;
                mtbZIPCode.Text = client.ZIPCode;
    
                WaterMeter meter = Repository.GetWaterMeter(strMeterNumber);
    
                txtMeterDetails.Text = meter.Make + " " +
                                       meter.Model +
                                       " (Meter #: " + meter.MeterSize + ")";
            }
    
            private void Details_FormClosing(object sender, FormClosingEventArgs e)
            {
                if (WaterDistribution.ViewBillDisplaying == true)
                {
                    WaterDistribution.ViewBillDisplaying = false;
                    Close();
                }
            }
        }
    }

83. To execute, on the main menu, click Debug -> Start Without Debugging:

    

84. On the main menu, click Water Meters and click View All Water Meters...:

    

85. On the main menu, click Water Meters and click Setup Water Meter...:

    

86. Enter the value for each of the following records and click Save Water Meter for each:

    Meter #	Make	Model	Meter Size
    392-44-572	Constance Technologies	TG-4822	5/8 Inches
    938-75-869	Stanford Trend	266G	1 1/2 Inches
    588-29-663	Estellano	NCF-226	3/4 Inches
    186-92-805	Lansome	2800	1 1/2 Inches
    799-28-461	Kensa Sons	K-584-L	3/4 Inches
    386-48-057	Estellano	NCF-226	3/4 Inches
    837-06-836	Lansome	7400	5/8 Inches
    207-94-835	Constance Technologies	TG-6220	5/8 Inches
    592-84-957	Kensa Sons	D-497-H	3/4 Inches
    374-06-284	Raynes Energica	i2022	3/4 Inches
    186-99-757	Kensa Sons	M-686-G	1 1/2 Inches
    630-07-055	Lansome	2800	3/4 Inches
    827-50-248	Standard Trend	428T	3/4 Inches
    470-68-850	Estellano	WRT-482	3/4 Inches
    649-33-505	Constance Technologies	BD-7000	5/8 Inches
    306-82-497	Lansome	9000	3/4 Inches

    

87. On the main menu, click Customers and click View All Accounts:

    

88. On the main menu, click Custoemrs and click Create Customer Account:

    

89. Using the values in the following table, enter an account number, then enter a meter number and click Find Water Meter. Complethe the record with the other values. Then click Save Customer Account:

    Account #	Meter #	First Name	Last Name	Address	City	County	State	ZIP-Code
    9279-570-8394	799-28-461	Thomas	Stones	10252 Broward Ave #D4	Frederick	Frederick	MD	21703-6628
    2068-258-9486	186-92-805	Ericka	Dellaney	4819 East Munk Street	Whitehall	Fulton	PA	17340-2277
    4820-375-2842	392-44-572	Akhil	Koumari	748 Red Hills Rd	Roanoke		VA	24012-9726
    6003-386-3955	374-06-284	Mandiakandara	Marmoudi	539 Avalon Court	Greenwood	Sussex	DE	19950-2288
    9249-379-6848	588-29-663	Richard	Eghert	8280 Sligo North Way	Albright	Preston	WV	26519-4626
    7518-302-6895	207-94-835	Grace	Brenner	4299 Peachtree Court	Rockville	Montgomery	MD	20853-1512
    3028-502-9418	186-99-757	Spencer	Kershaw	338C Grayson Street	Gatchellville	York	PA	17352-3808
    5293-957-3395	386-48-057	Kelly	Davids	10484 Greenway Avenue	Mt Storm	Grant	WV	26739-6242
    2038-413-9680	938-75-869	Amidou	Gomah	2075 Rose Hills Avenue	Washington		DC	20004-1818
    7028-405-9381	306-82-497	Jonathan	Simmings	613 Meadowhill Road	Alonzaville	Shenandoah	VA	22664-2662
    5938-074-5293	592-84-957	Marie	Rath	582G Dunhill Avenue	Lanham	Prince Georges	MD	20706-4422
    1827-395-0203	470-68-850	Sathyavanthara	Khooni	10331 Chryswell Road	Washington		DC	20008-5050
    8027-304-6829	837-06-836	Anthony	Clarcksons	904 Augusta Drive	Blackbird	New Castle	DE	19734-2606
    6699-396-2905	649-33-505	Spencer	Reuter	2850 Burnsweak Avenue	Silver Spring	Montgomery	MD	20910-7272
    7080-583-5947	827-50-248	Sandra	Moffat	663 Sherry Wood East Street	Shimpstown	Franklin	PA	17236-1116

    

90. On the main menu, click Water Bills and click Prepare Water Bill...

    

91. Fill the form with the following values:

    Water Bill #:             847384
    Account #: 	              3028-502-9418
    Meter Reading Start Date: 10/03/2022
    Meter Reading End Date:   01/06/2023
    Counter Reading Start:    16
    Counter Reading End:      21
    Billing Days:             95
    Payment Due Date:         01/21/2023
    Late Payment Due Date:    02/05/2023

    

92. Click Find Customer Account

    

93. Click Evaluate Water Bill

    

94. Click Save Water Bill
95. Follow the same steps to create records as follows:

    Water Bill #	Account #	Meter Reading Start Date	Meter Reading End Date	Counter Reading Start	Counter Reading End	Billing Days	Payment Due Date	Late Payment Due Date
    330820	7028-405-9381	10/03/2022	01/03/2023	9749	9906	92	01/18/2023	02/02/2023
    468550	7518-302-6895	10/05/2022	01/09/2023	96	114	96	01/24/2023	02/08/2023
    148274	9249-379-6848	10/05/2022	01/10/2023	260504	260555	97	01/25/2023	02/09/2023
    326384	2068-258-9486	10/08/2022	01/10/2023	104837	104851	94	01/25/2023	02/09/2023

96. On the main menu, click Water Bills and click View Water Bill
97. In the Water Bill # text box, type 468550
98. Click Find Water Bill
99. On the main menu, click Window and click Tile Vertical
100. On the main menu, click Window and click Tile Horizontal
101. On the main menu, click Window and click Cascade
102. On the main menu, click File and click Exit

Activating a Child

In most MDI applications, a user can create as many documents as necessary. This also means that the application can hold many child forms. To access a child form, the user can click its title bar. You can also provide options on a menu item named Window that would display a list of open documents.

When a child window is activated, it fires an event named MdiChildActivate:

public event EventHandler MdiChildActivate;

The MdiChildActivate event is of type EventArgs.

The document that is currently active has a brighter title bar. To identify this document, the form has a property named ActiveMdiChild. This read-only property allows you to know what document is the current active one. This property is of type Form, which means it produces a Form object. When you enquire about this property, if its value is null, it means there is no current active document. Here is an example of accessing the current active child document:

private void mnuFileClose_Click(object sender, EventArgs e)
{
    SingleDocument document = (SingleDocument)ActiveMdiChild;

    if( document  != null )
    {
        document.Close();
    }

    if (MdiChildren.Length== 0)
        mnuFileClose.Enabled = false;
}

If the value of the ActiveMdiChild property is not null, a document is active and you can use it. If you want to access the objects (Windows controls) that are positioned on a child form, remember that the child form is somehow foreign. Therefore, you should set the Modifiers property of its hosted controls approppriately. For example, if you want the parent frame to access a control on the child frame, set the Modifiers of that control to Public.

Arranging the Minimized Children

In an MDI application, if the user doesn't want to display a document but doesn't want to close it, he or she can minimise the window. In the same way, the user can minimize as many child forms as necessary. When a child form has been minimized, it shows a button in the lower part of the parent. The buttons of the other minimized child forms are usually positioned next to each other:

The user can move the buttons at will:

A user can also close the child form using the Close button of its minimized button. At one time the minimized buttons may display as a "mess". To let you rearrange them, call the LayoutMdi() method of the Form class and pass the argument as ArrangeIcons. When you do this, the application will visit all buttons, if any, that represent minimized child documents, and position them from the left to the right, adjacently.

Microsoft Visual Studio Assistance With MDI Applications

Microsoft Visual Studio makes it easy for you to create an MDI application. It doesn't do everything for you but it provides all the primary design you may need. It does this through the MDI Parent Form of the Add New Item dialog box.

Practical Learning: Ending the Application

• Close Microsoft Visual Studio

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