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How to: Handle Keyboard Input at the Form Level

How to: Handle Keyboard Input at the Form Level

Windows Forms provides the ability to handle keyboard messages at the form level, before the messages reach a control. This topic shows how to accomplish this task.

To handle a keyboard message at the form level

  • Handle the KeyPress or KeyDown event of the startup form, and set the KeyPreview property of the form to true so that keyboard messages are received by the form before they reach any controls on the form. The following code example handles the KeyPress event by detecting all of the number keys and consuming '1', '4', and '7'.

    
    ' Detect all numeric characters at the form level and consume 1, 
    ' 4, and 7. Note that Form.KeyPreview must be set to true for this
    ' event handler to be called.
    Sub Form1_KeyPress(ByVal sender As Object, _
        ByVal e As KeyPressEventArgs) Handles Me.KeyPress
    
        If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
            MessageBox.Show(("Form.KeyPress: '" + _
                e.KeyChar.ToString() + "' pressed."))
    
            Select Case e.KeyChar
                Case ChrW(49), ChrW(52), ChrW(55)
                    MessageBox.Show(("Form.KeyPress: '" + _
                        e.KeyChar.ToString() + "' consumed."))
                    e.Handled = True
            End Select
        End If
    End Sub
    
    
    

The following code example is the entire application for the above example. The application includes a TextBox along with several other controls that allow you to move focus from the TextBox. The KeyPress event of the main Form consumes '1', '4', and '7', and the KeyPress event of the TextBox consumes '2', '5', and '8' while displaying the remaining keys. Compare the MessageBox output when you press a number key while the TextBox has focus with the MessageBox output when you press a number key while focus is on one of the other controls.


Imports System
Imports System.Drawing
Imports System.Windows.Forms

Namespace KeyboardInputForm

     Class Form1
      Inherits Form

        Private WithEvents TextBox1 As New TextBox()

      <STAThread()> _
      Public Shared Sub Main()
         Application.EnableVisualStyles()
         Application.Run(New Form1())
      End Sub

      Public Sub New()
         Me.AutoSize = True

         Dim panel As New FlowLayoutPanel()
         panel.AutoSize = True
         panel.FlowDirection = FlowDirection.TopDown
         panel.Controls.Add(TextBox1)
         Me.Controls.Add(panel)

         Me.KeyPreview = True
        End Sub

        ' Detect all numeric characters at the form level and consume 1, 
        ' 4, and 7. Note that Form.KeyPreview must be set to true for this
        ' event handler to be called.
        Sub Form1_KeyPress(ByVal sender As Object, _
            ByVal e As KeyPressEventArgs) Handles Me.KeyPress

            If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
                MessageBox.Show(("Form.KeyPress: '" + _
                    e.KeyChar.ToString() + "' pressed."))

                Select Case e.KeyChar
                    Case ChrW(49), ChrW(52), ChrW(55)
                        MessageBox.Show(("Form.KeyPress: '" + _
                            e.KeyChar.ToString() + "' consumed."))
                        e.Handled = True
                End Select
            End If
        End Sub

      ' Detect all numeric characters at the TextBox level and consume  
      ' 2, 5, and 8.
      Sub TextBox1_KeyPress(ByVal sender As Object, _
          ByVal e As KeyPressEventArgs) Handles TextBox1.KeyPress

         If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
            MessageBox.Show(("Control.KeyPress: '" + _
                e.KeyChar.ToString() + "' pressed."))

            Select Case e.KeyChar
               Case ChrW(50), ChrW(53), ChrW(56)
                  MessageBox.Show(("Control.KeyPress: '" + _
                      e.KeyChar.ToString() + "' consumed."))
                  e.Handled = True
            End Select
         End If
      End Sub

   End Class
End Namespace


This example requires:

  • References to the System, System.Drawing and System.Windows.Forms assemblies.

For information about building this example from the command line for Visual Basic or Visual C#, see Building from the Command Line (Visual Basic) or Command-line Building With csc.exe. You can also build this example in Visual Studio by pasting the code into a new project. For more information, see How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio and How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio and How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio and How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio.

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