C# Using PostMessage

Question

I'm trying to send a key to an application. I tested the Handlewindow value used breakpoints to understand what I'm doing wirong but i cant find a solution. To be more detailed, its a little game and when I activate the chatbar ingame, the key I want to send will be written there, but I want to make it functionaly when I am playing to use the commands. The game doesnt have a guard or some protections.

Here is my code:

[DllImport("user32.dll")]
    static extern bool PostMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

    const uint WM_KEYDOWN = 0x0100;

    private void button1_Click(object sender, EventArgs e)
    {
        string pName = textBox1.Text;


        //Get Processes
        Process[] processes = Process.GetProcessesByName(pName);

        //Main part
        foreach (Process p in processes)
            if (p.ProcessName == (string)pName)
            {
                    PostMessage(p.MainWindowHandle, WM_KEYDOWN, (int)Keys.W, 0);
            }


    }

Like I said, it can be sent 1000000 times successfully but nothing happens. Is there another way how I can send keys to an Windows application that works minimized or even hidden? It should be only send to my app.

Answer 1

You can't fake messages like this and expect it to work reliably - all you are doing is sending a message, nothing fancy.

What this means is that if the target program tests for input in a different way (for example by directly checking the key state, reacting to different messages or just using a completely different mechanism) the target program at best may just completely ignore your input and at worst get totally confused.

Use the SendInput function instead (I'm not sure if this exposed as part of the .Net framework or not).

Some interesting blog articles which are fairly relevant:

• You can't simulate keyboard input with PostMessage
• Simulating input via WM_CHAR messages may fake out the recipient but it won't fake out the input system