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keybd_event (user32)
 
.
Summary
This function is useful to simulate Key presses to the window with focus.

Returns false, if there is an error simulating the key press.

C# Signature:

[DllImport("user32.dll")]
static extern bool keybd_event(byte bVk, byte bScan, uint dwFlags,
   UIntPtr dwExtraInfo);

or

[DllImport("user32.dll")]
static extern bool keybd_event(byte bVk, byte bScan, uint dwFlags,
   int dwExtraInfo);

VB.NET Signature:

<DllImport("user32.dll")> _
Private Shared Function keybd_event(bVk As Byte, bScan As Byte, dwFlags As UInteger, dwExtraInfo As UIntPtr) As Boolean
End Function

or

<DllImport("user32.dll")> _
Private Shared Function keybd_event(bVk As Byte, bScan As Byte, dwFlags As UInteger, dwExtraInfo As Integer) As Boolean
End Function

or

<DllImport("user32.dll", CallingConvention:=CallingConvention.StdCall, _
           CharSet:=CharSet.Unicode, EntryPoint:="keybd_event", _
           ExactSpelling:=True, SetLastError:=True)> _
Public Shared Function keybd_event(ByVal bVk As Byte, ByVal bScan As Byte, _
                              ByVal dwFlags As Int32, ByVal dwExtraInfo As Int32) As Boolean
End Function

VB Signature:

Public Declare Sub keybd_event Lib "user32" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long)

User-Defined Constants:

C#:

const uint KEYEVENTF_EXTENDEDKEY = 0x0001;
const uint KEYEVENTF_KEYUP = 0x0002;

VB.NET:

Const KEYEVENTF_EXTENDEDKEY As UInteger = &H1
Const KEYEVENTF_KEYUP As UInteger = &H2

VKs

http://msdn.microsoft.com/en-us/library/windows/desktop/dd375731(v=vs.85).aspx

User-Defined Types:

None

Notes:

None.

Tips & Tricks:

This function is useful to simulate Key presses (for input use the virtual keycodes from http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/WinUI/WindowsUserInterface/UserInput/VirtualKeyCodes.asp or windows CE universal core virtual key code compact chart http://msdn2.microsoft.com/en-us/library/ms927178.aspx ).

Use FindWindow and SetForegroundWindow to direct input to the desired window.

Note
WaitForInputIdle (Warning this will only wait once! See Raymond Chen's Blog Post http://blogs.msdn.com/b/oldnewthing/archive/2010/03/25/9984720.aspx ), or a Sleep may be required to assure Window is ready for input:

  RUN('NOTEPAD.EXE')
  Sleep(2000,0)
  SetForegroundWindow (FindWindow('Untitled - Notepad'))

(see also VkKeyScan):

    void PressKey( byte keyCode )
    {
        const int KEYEVENTF_EXTENDEDKEY = 0x1;
        const int KEYEVENTF_KEYUP       = 0x2;
        keybd_event( keyCode, 0x45, KEYEVENTF_EXTENDEDKEY, 0 );
        keybd_event( keyCode, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0 );
    }

C# Sample Code

// Sends ENTER button press event in focused window

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

using System.Runtime.InteropServices;
using System.Threading;

namespace PInvoke_DllImport_Cs
{
     public partial class Form1 : Form
     {
     public Form1()
     {
         InitializeComponent();
     }

     const byte VK_RETURN = 0x0D;

     const uint KEYEVENTF_KEYUP = 0x0002;

     [DllImport("user32.dll")]
     private static extern bool keybd_event(byte bVk, byte bScan, uint dwFlags, int dwExtraInfo);

     private void timer1_Tick(System.Object sender, System.EventArgs e)
     {
         keybd_event(VK_RETURN, 0, 0, 0);
         Thread.Sleep(100);
         keybd_event(VK_RETURN, 0, KEYEVENTF_KEYUP, 0);
     }
     }
}

VB.NET Sample Code 1

' Sends ENTER button press event in focused window

Imports System.Runtime.InteropServices
Imports System.Threading

Public Class Form1

     Const VK_RETURN As Byte = &HD '0x0D

     Const KEYEVENTF_KEYUP As UInteger = &H2 '0x0002

     <DllImport("user32.dll")> _
     Private Shared Function keybd_event(ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As UInteger, ByVal dwExtraInfo As Integer) As Boolean
     End Function

     'Public Declare Sub keybd_event Lib "user32" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long)

     Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
     keybd_event(VK_RETURN, 0, 0, 0)
     Thread.Sleep(100)
     keybd_event(VK_RETURN, 0, KEYEVENTF_KEYUP, 0)
     End Sub

End Class

VB.NET Sample Code 2:

This sample will generate a 'Scroll Lock' key press event when the user clicks 'Button1'.

  • Create a new Windows Application project;
  • Drop a button control in the recently created form;
  • Add the following code to the form class:

Imports System.Runtime.InteropServices

Public Class Form1

    <DllImport("user32.dll", CallingConvention:=CallingConvention.StdCall, _
           CharSet:=CharSet.Unicode, EntryPoint:="keybd_event", _
           ExactSpelling:=True, SetLastError:=True)> _
    Public Shared Sub keybd_event(ByVal bVk As Byte, ByVal bScan As Byte, _
                                  ByVal dwFlags As Integer, ByVal dwExtraInfo As Integer) As Boolean
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Const VK_SCROLL As Byte = &H91
        Const KEYEVENTF_KEYUP As Byte = &H2

        keybd_event(VK_SCROLL, 0x45, 0, 0)               ' Generates a KEY_DOWN
        keybd_event(VK_SCROLL, 0x45, KEYEVENTF_KEYUP, 0) ' Generates a KEY_UP

    End Sub

End Class

Please add some more!

Alternative Managed API: System.Windows.Forms.SendKeys

Documentation
keybd_event on MSDN

PROBLEM: How do i use combination of shift and tab keys at the same time ?

Answer:posted by dokks http://www.ravensmyst.com

define the shift key as a const

    public const byte VK_LSHIFT= 0xA0; // left shift key
    public const byte VK_TAB = 0x09;
    public const int KEYEVENTF_EXTENDEDKEY = 0x01;
    public const int KEYEVENTF_KEYUP = 0x02;

    //press the shift key
    keybd_event(VK_LSHIFT, 0x45, 0, 0);

    //press the tab key
    keybd_event(VK_TAB, 0x45, 0, 0);

    //release the tab key
    keybd_event(VK_TAB, 0x45, KEYEVENTF_KEYUP, 0);

    //release the shift key
    keybd_event(VK_LSHIFT, 0x45, KEYEVENTF_KEYUP, 0);

I'm using this to create automated UI testing for a custom Textbox control. After a lot of trial and error the following code worked well for me.

    public partial class Form2 : Form
    {
    [DllImport("user32.dll", SetLastError = true)]
    static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, UIntPtr dwExtraInfo);

    Keys[] numberKeys = new Keys[10] { Keys.D0, Keys.D1, Keys.D2, Keys.D3, Keys.D4, Keys.D5, Keys.D6, Keys.D7, Keys.D8, Keys.D9 };

    void PressKey(Keys key)
    {
        const int KEYEVENTF_EXTENDEDKEY = 0x1;
        const int KEYEVENTF_KEYUP = 0x2;
        // I had some Compile errors until I Casted the final 0 to UIntPtr like this...
        keybd_event((byte)key, 0x45, KEYEVENTF_EXTENDEDKEY, (UIntPtr)0);
        keybd_event((byte)key, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, (UIntPtr)0);
    }

    void PressKeyArray(Keys[] keys)
    {
        foreach (Keys key in keys)
        {
        PressKey(key);
        }
    }

    private void Compare(object sender, string expected, string actual)
    {
        Button ClickedButton = (Button)sender;

        if (expected == actual)
        ClickedButton.Text = "Pass";
        else
        ClickedButton.Text = "Fail";
    }

    private void buttonNumericAccept_Click(object sender, EventArgs e)
    {
        string expected = "0123456789";

        NumericTextbox.AcceptNumeric = true;

        //
        // Send Appropriate Key Presses
        //
        NumericTextbox.Focus();
        PressKeyArray(numberKeys);
        Application.DoEvents();

        // Process Results        
        Compare(sender, expected, NumericTextbox.Text);        
    }
    }

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