Chapter 4.LC, Problem 1RQ

Program Description Answer

The text box’s “KeyPress” event occurs when pressing any key in the keyboard.

Hence, correct answer is option “D”.

Explanation of Solution

The KeyPress event:

If a key is pressed within a control (i.e. the control has been focused), then the KeyPress event will occur.

• The keyPress event procedure sends the pressed key’s character to the “e” parameter of the keyPress event.
  • The acceptance of pressing key has been handled by using the property “Handled”.

e.Handled

• “Handled” property contains the Boolean values “True” or “False”.
• If the “Handled” property of the control is “true”, then the control cancels the pressed keys.

  e.Handled = True

• If the “Handled” property of the control is “false”, then the control accepts the pressed keys.

  e.Handled = False

Example:

The sub procedure “CancelKeys” allows the text boxes “txtCode” and “txtSales” to accept only the numbers and the backspace key.

Private Sub CancelKeys(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) _

Handles txtCode.KeyPress, txtSales.KeyPress

'Allows only numbers and the Backspace key in the 'text box

If (e.KeyChar < "0" OrElse e.KeyChar > "9") AndAlso e.KeyChar <> ControlChars.Back Then

    'Cancel the key

            e.Handled = True

        End If

    End Sub

The above example is used to accept only the numeric value keys and the backspace key.

Sample Output

Output:

Note: Here, it does not accept the keys other than the numeric and backspace key.

Enter “12” as code. Then, press backspace key to delete the 2.

Screenshot of “Bonus Calculator” form

The 2 will be deleted after pressing the backspace key.

Screenshot of “Bonus Calculator” form