KeyPressEventHandler Delegate

 

Represents the method that will handle the KeyPress event of a Control.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

Public Delegate Sub KeyPressEventHandler (
	sender As Object,
	e As KeyPressEventArgs
)

Parameters

sender
Type: System.Object

The source of the event.

e
Type: System.Windows.Forms.KeyPressEventArgs

A KeyPressEventArgs that contains the event data.

Set KeyPressEventArgs.Handled to true to cancel the KeyPress event. This keeps the control from processing the key press.

When you create a KeyPressEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about handling events with delegates, see Handling and Raising Events.

Imports System
Imports System.Windows.Forms

Public Class Form1
    Inherits Form

    Public Sub New()
        ' Create a TextBox control.
        Dim tb As New TextBox()
        Me.Controls.Add(tb)
        AddHandler tb.KeyPress, AddressOf keypressed
    End Sub 'NewNew

    Private Sub keypressed(ByVal o As [Object], ByVal e As KeyPressEventArgs)
        ' The keypressed method uses the KeyChar property to check 
        ' whether the ENTER key is pressed. 

        ' If the ENTER key is pressed, the Handled property is set to true, 
        ' to indicate the event is handled.

        If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Return) Then
            e.Handled = True
        End If
    End Sub 'keypressed

    Public Shared Sub Main()
        Application.Run(New Form1())
    End Sub 'Main
End Class 'Form1
' Boolean flag used to determine when a character other than a number is entered.
Private nonNumberEntered As Boolean = False


' Handle the KeyDown event to determine the type of character entered into the control.
Private Sub textBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
     Handles textBox1.KeyDown
    ' Initialize the flag to false.
    nonNumberEntered = False

    ' Determine whether the keystroke is a number from the top of the keyboard.
    If e.KeyCode < Keys.D0 OrElse e.KeyCode > Keys.D9 Then
        ' Determine whether the keystroke is a number from the keypad.
        If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
            ' Determine whether the keystroke is a backspace.
            If e.KeyCode <> Keys.Back Then
                ' A non-numerical keystroke was pressed. 
                ' Set the flag to true and evaluate in KeyPress event.
                nonNumberEntered = True
            End If
        End If
    End If
    'If shift key was pressed, it's not a number.
    If Control.ModifierKeys = Keys.Shift Then
        nonNumberEntered = true
    End If
End Sub 'textBox1_KeyDown


' This event occurs after the KeyDown event and can be used 
' to prevent characters from entering the control.
Private Sub textBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) _
    Handles textBox1.KeyPress
    ' Check for the flag being set in the KeyDown event.
    If nonNumberEntered = True Then
        ' Stop the character from being entered into the control since it is non-numerical.
        e.Handled = True
    End If
End Sub 'textBox1_KeyPress

.NET Framework
Available since 1.1
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