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Messages and Events of Windows Controls
 

Controls Messages
 

Introduction

We saw that Windows controls are added to a spreadsheet or a form to help a person interact with the computer. When one of these controls is used, it must communicate with the operating system. For example, when a user clicks, the object that was clicked must inform the operating system that it has been clicked. This is the case for every control used in an application. Because a typical application can involve many controls, a mechanism was designed to manage this.

To communicate its intention to the operating system, a Windows control must compose a message and deliver it (to the operating system).
 

The Parts of a Message

In order to make a message clear, the control that wants to send it must provide three important pieces of information:

  • WHO sent the message? When a control sends a message, it must identify itself because there can be many controls sending different messages at the same time. The operating system will need to know where a message came from. This is one of the reasons why every control must have a name. Also because each message is particular to the control that sent it, the message is considered a private matter.
    Based on this, the code of a message starts with Private Sub, followed by the name of the control that is sending the message:
     
    Private Sub ControlName
  • WHAT message? When a control is sending a message, it must specify the type of message. A control can be able to send various types of messages. For example, when a control gets clicked, it sends a Click message. If the same control receives focus but the user presses a key, the control sends a keyboard-related message. When the mouse passes over that same control, its sends a different type of message.
    Every message a control can send has a name. To see the types of message available for a particular control, open Microsoft Visual Basic. In the Object combo box, select the name of the control. Then, click the arrow of the Procedure combo box:
     

     
    By convention, the name of the message follows the name of the control but they are separated with an underscore. It would appear as:
     
    Private Sub ControlName_Push
  • Arguments: An argument is additional information needed to process a message. When a control sends a message, it may need to accompany it with some information. For example, if the user positions the mouse on a control and clicks, the operating system may need to know what button of the mouse was used to click. On the other hand, if the user selects an object and starts dragging, the operating system may need to know if a key such as Shift or Ctrl was held down while the user was dragging.
    An additional piece of information that the control provides is called an argument. While some messages may need to provide only one piece of information, some messages would require more than one argument. Some other messages don't need any additional information at all: the name of the message would completely indicate how the message must be processed.
    The arguments of a message are provided in parentheses. They would appear as:
     
    Private Sub ControlName_Push(Argument1, Argument2, Argument_n)

After specifying the message, you can type code that tells the operating system what to do to process the message. To indicate the end of the code that relates to a message, type End Sub

Private Sub ControlName_Push(Argument1, Argument2, Argument_n)
      
End Sub

As mentioned earlier, a message must be composed and sent. The action of sending a message is called an event. It is also said that the controls "fires" an event. Based on the above descriptions, to compose and send a message, in the Object combo box, you can select the name of the control that will send the message, then select the desired message in the Procedure combo box. When you do this, Microsoft Visual Basic will write the first line that specifies the name of the control, the name of the event, its arguments if any, and would write End Sub for you. You can then enter the necessary code between those two lines.

Most Windows control have a special event referred to as the default. This is the even that is the most obvious that the control can fire. For example, when you think of a button, the first action that comes to mind is Click. For this reason, Click is the default event of a button. If you add a control to a spreadsheet or a form and double-click the control, its default event would be invoked and the skeleton of that event would be written in the corresponding module. If you don't want to use that event or to fires another event for the same control, you can simply select the event in the Procedure combo box.

Practical Learning Practical Learning: Introducing Messages and Events
  1. Start Microsoft Excel
  2. To open Microsoft Visual Basic, on the main menu, click Tools -> Visual Basic Editor
  3. To create a form, on the Standard toolbar, click the Insert UserForm button
  4. On the Toolbox, click the TextBox and click the form
  5. Right-click the new text box and click Properties
  6. Click (Name) and type txtFullName
  7. Click the form. Again, on the Toolbox, click the CommandButton and click the form away from the previously added text box
  8. In the Properties window, click (Name) and type cmdSend
  9. Click Caption and type Send Time Sheet
  10. Click the form. Once again, on the Toolbox, click the ComboBox and click the form away from the previously added controls
  11. In the Properties window, click (Name) and type cboGrades

Common Events of Windows Controls
 

Click

To interact with the computer, one of the most usually performed actions is to click. The mouse is equipped with two buttons. The most clicked button is the left one.

Because the action simply consists of clicking, when the user presses this button, a simple event, called Click is sent or fired. When the user presses the (left) button on the mouse, the mouse pointer is usually on a Windows control. Based on this, the control that is clicked "owns" the event and must manage it. Therefore, no detailed information is provided as part of the event. The operating system believes that the control that fired the event knows what to do and should take care of everything. For this reason, whenever you decide to code an OnClick event, you should make sure you know what control sent or fired the event. This is (one of) the most common events of Windows controls.

Practical Learning Practical Learning: Generating a Click Event

Double-Click

Another common action the user performs on a control may consist of double-click it. This action causes the control to fire an event known as DblClick.

Practical Learning Practical Learning: Generating a Double-Click Event

Getting Focus

Just as an application can have many forms, a form can be equipped with various controls. Such is the case for any data entry form. On a form that is equipped with many controls, only one control can be changed at a time; such a control is said to have focus. To give focus to a control, the user can click it or can keep pressing Tab until the desired control indicates that it has focus. In a form with many controls, the control that has focus may display a caret or a dotted line around its selection or its caption.

When a form or a control receives focus, it fires the GotFocus event. We mentioned that a user can give focus to a control by clicking it. If the control is text-based, then a caret blinking in the control indicates that the control has focus. When a text-based control receives focus, it fires an Enter event.
 

Practical Learning Practical Learning: Generating an Enter Event
  1. In the Object combo box, select txtFullName
  2. In the Procedure combo box, select Enter and notice what the event looks like:
      
    Private Sub txtFullName_Enter()

End Sub
 

Losing Focus

After using a control, the user can switch to another control either by clicking another or by pressing Tab. This causes the focus to shift from the current control to another. If the focus shifts to another control, the control that had focus fires a LostFocus event. If the control is text-based, when the focus moves away from that control, for example if the user presses Tab from the control, that controls fires an Exit event.
 

Practical Learning Practical Learning: Losing Focus
  1. In the Object combo box, select cboGrades
  2. In the Procedure combo box, select Exit and notice the structure of the event:
      
    Private Sub cboGrades_Exit(ByVal Cancel As MSForms.ReturnBoolean)

End Sub

Keyboard Events

Word processing consists of manipulating text and characters on your computer until you get the fantastic result you long for. To display these characters, you press some keys on your keyboard. If the application is configured to receive text, your pressing actions will display characters on the screen. The keyboard is also used to perform various other actions such as accepting what a dialog box displays or dismissing it.

When the user presses the keys on a keyboard, the control in which the characters are being typed sends one or more messages to the operating system. There are three main events that Microsoft Windows associates to the keyboard.

  • KeyDown: When the user presses a key on the keyboard, an event called KeyDown is fired.

  • KeyUp: When the user releases a key that was pressed, an even called KeyUp fires. These previous two events apply to almost any key on the keyboard, even if the user is not typing; that is, even if the result of pressing a key did not display a character on the document.

  • KeyPress: The KeyPress event fires if the key the user pressed is recognized as a character key; that is, a key that would result in displaying a character in a document.

Some keys on the keyboard don't display anything on a document. Instead, they perform (only) an action. Examples of such keys are Enter, Tab, Esc. Therefore, if you mean to find out what key the user pressed, use the KeyDown instead of the KeyPress event, even though the user will have pressed a key.

Practical Learning Practical Learning: Generating a Keyboard event
  1. In the Object combo box, select txtFullName
  2. In the Procedure combo box, select KeyDown and observe what the code of the event looks like:
      
    Private Sub txtFullName_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)

End Sub
 

MouseDown

A mouse is equipped with buttons, usually two, that the user presses to request an action. Compared to the keyboard, the mouse claims many more events that are directly or indirectly related to pressing one of its buttons.

When the user presses one of the buttons on the mouse, an event, called MouseDown fires. This event carries enough information for the programmer as three arguments. 

 
Private Sub txtFirstName_MouseDown(Button As Integer, Shift As Integer,
      X As Single, Y As Single)

End Sub
  • The operating system needs to know what button was pressed; this is represented as the left or the right button. The left button is known as vbLeftButton. The right button is referenced as vbRightButton. If the mouse is equipped with a middle button, it would vbMiddleButton. In reality, these buttons have (constant) numeric values of 0, 1, and 2 respectively.
  • Secondly, the operating system needs to know whether a special key, Shift, Ctrl, or Alt, was pressed. These buttons are called vbShiftMask, vbCtrlMask, and vbAltMask respectively. In reality, they are represented with 1, 2, and 4 respectively.
  • Lastly, the operating system needs to know the screen coordinates of the mouse pointer, that is, the coordinates of the point where the mouse landed. X represents the distance from the top left corner of the parent to the mouse. Y represents the vertical measure of the point from the top-left corner down.
 

Practical Learning Practical Learning: Generating a Mouse Down event
  1. In the Object combo box, select cmdSend
  2. In the Procedure combo box, select MouseDown:
      
    Private Sub cmdSend_MouseDown(ByVal Button As Integer, ByVal Shift As Integer, ByVal X As Single, ByVal Y As Single)

End Sub
 

MouseUp

When the user releases a button that was pressed on the mouse, a new event fires. This event is called MouseUp. It provides the same types of information as the MouseDown event:

 
Private Sub txtFirstName_MouseUp(Button As Integer, Shift As Integer,
      X As Single, Y As Single)

End Sub

MouseMove

The MouseMove event is sent while the user is moving the mouse on a control. It provides the same pieces of information as the MouseDown and the MouseUp events:

 
Private Sub txtFirstName_MouseMove(Button As Integer, Shift As Integer,
      X As Single, Y As Single)

End Sub

Practical Learning Practical Learning: Closing Microsoft Excel
  1. Close Microsoft Excel
  2. When asked whether you want to save the changes, click No
 
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