C# KEYEVENTF_KEYUP doesn't work in specific app

Question

I need to emulate some keys, here the code:

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

private const int KEYEVENTF_EXTENDEDKEY = 1;
private const int KEYEVENTF_KEYUP = 2;

public static void KeyDown(Keys vKey)
{
    keybd_event((byte)vKey, 0, KEYEVENTF_EXTENDEDKEY, 0);
}

public static void KeyUp(Keys vKey)
{
    keybd_event((byte)vKey, 0, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
}

KeyboardSend.KeyDown(Keys.Z);
KeyboardSend.KeyUp(Keys.Z);

But in one specific application "KeyUp" method doesn't work and is depressed until i press key on keyboard.

What i'm doing wrong?

Answer 1

When I changed the code to the following it seemed to work just fine. I tested it by opening notepad, running the program, then holding down the 'a' key. It printed lowercase for 3 seconds, then started doing uppercase then went back to lowercase again.

public static void KeyDown(Keys vKey)
{
    keybd_event((byte)vKey, 0, 0, 0);
}

public static void KeyUp(Keys vKey)
{
    keybd_event((byte)vKey, 0, KEYEVENTF_KEYUP, 0);
}

System.Threading.Thread.Sleep(3000);
KeyDown(Keys.SHIFT);
System.Threading.Thread.Sleep(4000);
KeyUp(Keys.SHIFT);

Try checking out Windows Input Simulator for a good example of how to simulate key presses. It's an open source wrapper for the SendInput function in User32.dll.

One thing I've learned is that to simulate holding a key down, it usually isn't enough to send the keydown, wait a bit, then send the key up. If you want the key to repeat the key press like a normal keyboard does you have to keep sending the keyboard event and end it with a key up event.

http://inputsimulator.codeplex.com/

Answer 2

The only change I see in Ryan West 's solution, is that he removed the KEYEVENTF_EXTENDEDKEY flag away from calling function keybd_event in the third argument, in both KeyDown and KeyUp methods, so as a result, in KeyDown method, the third argument of calling keybd_event function is 0, and in KeyUp method, it is only KEYEVENTF_KEYUP . That only small change caused KeyUp method to work and solve your problem.

Read about keybd_event function in MSDN site properly , and even again , if you read before.

They give information and details about that function and its arguments. They also explain all the flags that you can use in the third argument of keybd_event function, especially the case in your problem KEYEVENTF_EXTENDEDKEY .

If you will read properly and again , maybe you will understand why KEYEVENTF_EXTENDEDKEY flag causes your KeyUp method not to work, and why you have to remove that flag, in order to cause your KeyUp method to work.

You may also learn how, in the future , to call keybd_event function correctly , so you won't get any problem with it.