KeyPressEventArgs Class (System.Windows.Forms)

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Microsoft Visual Studio 2008/.NET Framework 3.5

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.NET Framework Class Library

KeyPressEventArgs Class

Provides data for the KeyPress event.

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

Syntax

Visual Basic (Declaration)

<ComVisibleAttribute(True)> _
Public Class KeyPressEventArgs _
    Inherits EventArgs

Visual Basic (Usage)

Dim instance As KeyPressEventArgs

[ComVisibleAttribute(true)]
public class KeyPressEventArgs : EventArgs

Visual C++

[ComVisibleAttribute(true)]
public ref class KeyPressEventArgs : public EventArgs

/** @attribute ComVisibleAttribute(true) */
public class KeyPressEventArgs extends EventArgs

JScript

public class KeyPressEventArgs extends EventArgs

Remarks

A KeyPressEventArgs specifies the character that is composed when the user presses a key. For example, when the user presses SHIFT + K, the KeyChar property returns an uppercase K.

A KeyPress event occurs when the user presses a key. Two events that are closely related to the KeyPress event are KeyUp and KeyDown. The KeyDown event precedes each KeyPress event when the user presses a key, and a KeyUp event occurs when the user releases a key. When the user holds down a key, duplicate KeyDown and KeyPress events occur each time the character repeats. One KeyUp event is generated upon release.

With each KeyPress event, a KeyPressEventArgs is passed. A KeyEventArgs is passed with each KeyDown and KeyUp event. A KeyEventArgs specifies whether any modifier keys (CTRL, SHIFT, or ALT) were pressed along with another key. (This modifier information can also be obtained through the ModifierKeys property of the Control class.)

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

Note:
Some controls will process certain key strokes on KeyDown. For example, RichTextBox processes the Enter key before KeyPress is called. In such cases, you cannot cancel the KeyPress event, and must cancel the key stroke from KeyDown instead.

For information about the event model, see Events and Delegates.

Examples

The following example illustrates using the KeyPressEventArgs to count keys as they are pressed and to display the results after each key press. Handled is then set to true to keep the operating system from further processing the key. The example assumes a form with a TextBox placed on it.

Visual Basic

Public Class myKeyPressClass
    Private Shared keyPressCount As Long = 0
    Private Shared backspacePressed As Long = 0
    Private Shared returnPressed As Long = 0
    Private Shared escPressed As Long = 0
    Private textBox1 As TextBox

    Private Sub myKeyCounter(sender As Object, ex As KeyPressEventArgs)
        Select Case ex.KeyChar
            ' Counts the backspaces.
            Case ControlChars.Back
                backspacePressed = backspacePressed + 1
            ' Counts the ENTER keys.
            Case ControlChars.Lf
                returnPressed = returnPressed + 1
            ' Counts the ESC keys.  
            Case Convert.ToChar(27)
                escPressed = escPressed + 1
            ' Counts all other keys.
            Case Else
                keyPressCount = keyPressCount + 1
        End Select

        textBox1.Text = backspacePressed & " backspaces pressed" & _
            ControlChars.Lf & ControlChars.Cr & escPressed & _
            " escapes pressed" & ControlChars.CrLf & returnPressed & _
            " returns pressed" & ControlChars.CrLf & keyPressCount & _
            " other keys pressed" & ControlChars.CrLf
        ex.Handled = True
    End Sub 'myKeyCounter
End Class 'myKeyPressClass

public class myKeyPressClass 
 {
     static long keyPressCount = 0 ;
     static long backspacePressed =  0;
     static long returnPressed = 0 ;
     static long escPressed = 0 ;
     private TextBox textBox1 = new TextBox();
     private void myKeyCounter(object sender, KeyPressEventArgs ex)
     {
     switch(ex.KeyChar)
     {
             // Counts the backspaces.
         case '\b':
         backspacePressed = backspacePressed + 1;
         break ;
             // Counts the ENTER keys.
         case '\r':
         returnPressed = returnPressed + 1 ;
         break ;
             // Counts the ESC keys.  
         case (char)27:
         escPressed = escPressed + 1 ;
         break ;
             // Counts all other keys.
         default:
         keyPressCount = keyPressCount + 1 ;
         break;
     }

     textBox1.Text = 
         backspacePressed + " backspaces pressed\r\n" + 
         escPressed + " escapes pressed\r\n" +
         returnPressed + " returns pressed\r\n" +
         keyPressCount + " other keys pressed\r\n" ;
     ex.Handled = true ;
     }
 }

Visual C++

public ref class myKeyPressClass
{
private:
   static long keyPressCount = 0;
   static long backspacePressed = 0;
   static long returnPressed = 0;
   static long escPressed = 0;
   TextBox^ textBox1;
   void myKeyCounter( Object^ sender, KeyPressEventArgs^ ex )
   {
      switch ( ex->KeyChar )
      {
            // Counts the backspaces.
         case '\b':
         backspacePressed = backspacePressed + 1;
         break;

            // Counts the ENTER keys.
         case '\r':
         returnPressed = returnPressed + 1;
         break;

            // Counts the ESC keys.  
         case (char)27:
         escPressed = escPressed + 1;
         break;

            // Counts all other keys.
         default:
         keyPressCount = keyPressCount + 1;
         break;
      }
      textBox1->Text = String::Concat( 
         backspacePressed, " backspaces pressed\r\n",
         escPressed, " escapes pressed\r\n",
         returnPressed, " returns pressed\r\n",
         keyPressCount, " other keys pressed\r\n" );
      ex->Handled = true;
   }
};

public class MyKeyPressClass
{
    private static long keyPressCount = 0;
    private static long backspacePressed = 0;
    private static long returnPressed = 0;
    private static long escPressed = 0;
    private TextBox textBox1 =  new TextBox();

    private void MyKeyCounter(Object sender, KeyPressEventArgs ex)
    {
        switch(ex.get_KeyChar()) {
            // Counts the backspaces.
            case 'b' : 
                backspacePressed = backspacePressed + 1;
                break;
            // Counts the ENTER keys.
            case 'r' : 
                returnPressed = returnPressed + 1;
                break;
            // Counts the ESC keys.  
            case (char)(27) : 
                escPressed = escPressed + 1;
                break;
            default : 
                // Counts all other keys.
                keyPressCount = keyPressCount + 1;
                break;
        }

        textBox1.set_Text(backspacePressed + " backspaces pressed\r\n"
            + escPressed + " escapes pressed\r\n" + returnPressed
            + " returns pressed\r\n"+keyPressCount + " other keys pressed\r\n");
        ex.set_Handled(true);
    } //MyKeyCounter
} //MyKeyPressClass

You must create a new instance of this class. You must also set the event handler. You can do this in the constructor for your class.

Visual Basic

Private myKeyPressHandler As New myKeyPressClass()

Public Sub New()
    InitializeComponent()

    AddHandler textBox1.KeyPress, AddressOf myKeyPressHandler.myKeyCounter
End Sub 'New

myKeyPressClass myKeyPressHandler = new myKeyPressClass();
public Form1()
{
     InitializeComponent();

     textBox1.KeyPress += new KeyPressEventHandler(myKeyPressHandler.myKeyCounter);
}

Visual C++

public:
   myKeyPressClass^ myKeyPressHandler;

   Form1()
   {
      myKeyPressHandler = gcnew myKeyPressClass;

      InitializeComponent();

      textBox1->KeyPress += gcnew KeyPressEventHandler(
         myKeyPressHandler, &myKeyPressClass::myKeyCounter );
   }

private MyKeyPressClass myKeyPressHandler = new MyKeyPressClass();
public Form1()
{
    InitializeComponent();
    textBox1.add_KeyPress(new KeyPressEventHandler(myKeyPressHandler.
        MyKeyCounter));
} //Form1

When the specified event is raised in the control, the attached method is called and the application can execute code in response to the event.

Inheritance Hierarchy

System..::.Object
System..::.EventArgs
System.Windows.Forms..::.KeyPressEventArgs

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information