Check Box Characteristics

Checking a Check Box

By default, a check box appears empty, which makes its statement false. To make the statement true, the user can click it. There are three main ways you can use this property of a check box. To select a check box, you can set its Checked property to True. You can also do it programmatically as follows:

private void Form1_Load(object sender,
			System.EventArgs e)
{
        checkBox1.Checked = true;
}

To find out if an item is selected, get the value of its Checked property. Another possibility consists of toggling the state of the check mark. For example, you can check or uncheck the check mark when the user clicks another button. To do this, you can simply negate the truthfulness of the control as follows:

checkBox1.Checked = ! checkBox1.Checked;

Like the radio button, when a check box is clicked, the control fires a CheckedChanged event to let you know that it has been checked. This event is of type EventArgs. If the check box can display only two states, checked or unchecked, this event is enough.

1. On the form click the Small radio button
2. Press and hold Shift
3. Click the Medium radio button, the Large radio button, the Pepperoni, the Sausage, the Extra Cheese, the Olives, and the Onions check boxes
4. Release Shift
5. In the Properties window, click the Events button
6. In the Events section, double-click Click
7. Return to the form
8. Click the txtSmall text box
9. Press and hold Shift
10. Click each of the following controls: txtMedium, txtLarge, txtEachTopping, txtQtyBread, txtPriceBread, txtQtyWings, txtPriceWince, txtQtyCan, txtPriceCan, txtQtySoda20, txtPriceSoda20, txtQtySoda2L, txtPriceSoda2L, txtQtyOJ, txtPriceOJ, txtQtyWater, and txtPriceWater
11. Release Shift
12. In the Events section of the Properties window, double-click Leave
13. In the Code Editor, define a method named CalculatePrice() and implement the events as follows:
     

    using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace DaniloPizza1 { public partial class Exercise : Form { public Exercise() { InitializeComponent(); } internal void CalculatePrice() { double PriceSize = 0.00; double PriceEachTopping = 0.00, BWings, Bread, SodaCan, Soda20, Soda2L, OJ, Water, PriceToppings, TotalOrder; int Pepperoni, Sausage, ExtraCheese, Onions, Olives; try { // Get the price of pizza depending on the selected size if (rdoSmall.Checked == true) PriceSize = double.Parse(txtSmall.Text); if (rdoMedium.Checked == true) PriceSize = double.Parse(txtMedium.Text); if (rdoLarge.Checked == true) PriceSize = double.Parse(txtLarge.Text); } catch (FormatException) { MessageBox.Show("The value you typed for the price " + "of a pizza is invalid" + "\nPlease try again"); } // Get the price of a topping if it was selected if (chkPepperoni.Checked == true) Pepperoni = 1; else Pepperoni = 0; if (chkSausage.Checked == true) Sausage = 1; else Sausage = 0; if (chkExtraCheese.Checked == true) ExtraCheese = 1; else ExtraCheese = 0; if (chkOnions.Checked == true) Onions = 1; else Onions = 0; if (chkOlives.Checked == true) Olives = 1; else Olives = 0; // Get the price of each topping try { PriceEachTopping = double.Parse(txtEachTopping.Text); } catch (FormatException) { MessageBox.Show("The value you typed for the price of " + "a each topping is invalid" + "\nPlease try again"); } PriceToppings = (Pepperoni + Sausage + ExtraCheese + Onions + Olives) * PriceEachTopping; // Calculate the price of the side dishes // depending on the quantity entered BWings = double.Parse(txtTotalWings.Text); Bread = double.Parse(txtTotalBread.Text); // Calculate the price of the drink(s) SodaCan = double.Parse(txtTotalCan.Text); Soda20 = double.Parse(txtTotalSoda20.Text); Soda2L = double.Parse(txtTotalSoda2L.Text); OJ = double.Parse(txtTotalOJ.Text); Water = double.Parse(txtTotalWater.Text); TotalOrder = PriceSize + PriceToppings + BWings + Bread + SodaCan + Soda20 + Soda2L + OJ + Water; txtTotalOrder.Text = TotalOrder.ToString("F"); } private void rdoSmall_Click(object sender, EventArgs e) { CalculatePrice(); } private void txtSmall_Leave(object sender, EventArgs e) { int QtyBread = 0, QtyWings = 0, QtyCan = 0, QtySoda20 = 0, QtySoda2L = 0, QtyOJ = 0, QtyWater = 0; double PriceBread = 0.00, TotalBread = 0.00, PriceWings = 0.00, TotalWings = 0.00, PriceCan = 0.00, TotalCan = 0.00, PriceSoda20 = 0.00, TotalSoda20 = 0.00, PriceSoda2L = 0.00, TotalSoda2L = 0.00, PriceOJ = 0.00, TotalOJ = 0.00, PriceWater = 0.00, TotalWater = 0.00; // Retrieve the quantity set in the text box try { QtyBread = int.Parse(txtQtyBread.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the " + "quantify of bread sticks is not valid" + "\nPlease try again!"); } // Get the unit price of the item try { PriceBread = double.Parse(txtPriceBread.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "bread sticks is not valid" + "\nPlease try again!"); } // Calculate the sub-total of this item TotalBread = QtyBread * PriceBread; // Display the sub-total in the corresponding text box txtTotalBread.Text = TotalBread.ToString("F"); try { PriceWings = int.Parse(txtQtyWings.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of orders of buffalo wings is not valid" + "\nPlease try again!"); } try { PriceWings = double.Parse(txtPriceWings.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "buffalo wings is not valid" + "\nPlease try again!"); } TotalWings = QtyWings * PriceWings; txtTotalWings.Text = TotalWings.ToString("F"); try { QtyCan = int.Parse(txtQtyCan.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of soda cans is not valid" + "\nPlease try again!"); } try { PriceCan = double.Parse(txtPriceCan.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "soda cans is not valid" + "\nPlease try again!"); } TotalCan = QtyCan * PriceCan; txtTotalCan.Text = TotalCan.ToString("F"); try { QtySoda20 = int.Parse(txtQtySoda20.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of soda 20 Oz. is not valid" + "\nPlease try again!"); } try { PriceSoda20 = double.Parse(txtPriceSoda20.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "soda 20 Oz. is not valid" + "\nPlease try again!"); } TotalSoda20 = QtySoda20 * PriceSoda20; txtTotalSoda20.Text = TotalSoda20.ToString("F"); try { QtySoda2L = int.Parse(txtQtySoda2L.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify of " + "bottles of soda 2-litter is not valid" + "\nPlease try again!"); } try { PriceSoda2L = double.Parse(txtPriceSoda2L.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of a " + "bottle of soda is not valid" + "\nPlease try again!"); } TotalSoda2L = QtySoda2L * PriceSoda2L; txtTotalSoda2L.Text = TotalSoda2L.ToString("F"); try { QtyOJ = int.Parse(txtQtyOJ.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of a bottle of orange juice is not valid" + "\nPlease try again!"); } try { PriceOJ = double.Parse(txtPriceOJ.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "bottles of orange is not valid" + "\nPlease try again!"); } TotalOJ = QtyOJ * PriceOJ; txtTotalOJ.Text = TotalOJ.ToString("F"); try { QtyWater = int.Parse(txtQtyWater.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of bottles of water is not valid" + "\nPlease try again!"); } try { PriceWater = double.Parse(txtPriceWater.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "bottle of water is not valid" + "\nPlease try again!"); } TotalWater = QtyWater * PriceWater; txtTotalWater.Text = TotalWater.ToString("F"); CalculatePrice(); } private void btnClose_Click(object sender, EventArgs e) { Close(); } } }

14. Return to the and double-click the Close button
15. Implement its Click event as follows:
     

    private void btnClose_Click(object sender, System.EventArgs e) { Close(); }

16. Execute the application and test the form. Here is an example:
     
    
17. Close the form and return to your programming environment

By default, the square box of a check control is positioned to the left side of its accompanying label. Instead of this default left position, you can change as you wish. The position of the round box with regards to its label is controlled by the CheckAlign property that of type ContentAlignment. To programmatically set the check alignment of a check box, you can call the ContentAlignment enumeration and select the desired value. Here is an example:

private void Form1_Load(object sender, System.EventArgs e)
{
	this.checkBox1.Checked = true;
	this.checkBox1.CheckAlign = ContentAlignment.MiddleRight;
}

Instead of being definitely checked, you can let the user know that the decision of making the statement true or false is not complete. This means that a check box can display as "half-checked". In this case the check mark would appear as if it were disabled. This behavior is controlled through the CheckState property. To provide this functionality, assign the Indeterminate value to its CheckState property. You can do this programmatically as follows:

this.ccheckBox1.CheckState = checkState.Indeterminate;

The CheckState property only allows setting the check box control as "undecided". If you actually want the user to control three states of the control as checked, half-checked, or unchecked, use the ThreeState property.

By setting the CheckState Boolean property to true, the user can click it two to three times to get the desired value. When this ability is given to the user, you can use or check the value of the Indeterminate property to find out whether the control is checked, half-checked, or unchecked.

Here is an example of specifying the check box control as being able to display one of three states:

private void Form1_Load(object sender, System.EventArgs e)
{
	checkBox1.Checked = true;
	checkBox1.ThreeState = true;
}

If a check box is configured to assume one of three states when it's clicked, that is, if the ThreeState property of a check button is set to True, when the user clicks such a button, the button acquires one of the available three states, which are Checked, Unchecked, or Indeterminate. This causes the control to fire a CheckStateChanged event. This event also is of type EventArgs. This means that it does not let you know the current state of the button. You would have to find it out yourself, which is easily done by getting the value of the CheckState property.

By default, a check box appears as a square box that gets a check mark when the user clicks it. Optionally, you can make a check box appear as a toggle button. In that case, the button would appear as a regular button. When the user clicks it, it appears down. If the user clicks it again, it becomes up.

To change the appearance of a check box, assign the Button or Normal value to its Appearance property. The Appearance values are defined in the Appearance enumeration. You can also do this programmatically as follows:

private void Form1_Load(object sender, System.EventArgs e)
{
	checkBox1.Checked = true;
	checkBox1.ThreeState = true;
	checkBox1.Appearance = Appearance.Button;
}

Like the radio button, the check box control fires an AppearanceChanged event when the button's appearance changes from Normal to Button or vice-versa.

Applications

Boolean Algebra