Simulate keyboard click in GTA:SA

Question

I'm trying to run a program that sometimes will simulate clicks in GTA:SA. Problem is it doesn't do anything when running. I have tried this code so far:

IntPtr calculatorHandle = FindWindow(null, "GTA:SA:MP");
if (calculatorHandle == IntPtr.Zero)
{
    MessageBox.Show("GTA:SA:MP isn't running");
    return;
}
SetForegroundWindow(calculatorHandle);
SendKeys.SendWait("T123");

I'd be glad if you tell if something is wrong with my code. Thanks!

EDIT

This is my code after adding Neill's code:

IntPtr calculatorHandle = FindWindow(null, "GTA:SA:MP");
if (calculatorHandle == IntPtr.Zero)
{
    MessageBox.Show("GTA:SA:MP isn't running");
    return;
}
SetForegroundWindow(calculatorHandle);
short key = 0x14;
WindowsMessageService.SendKey(key, KeyFlag.KeyDown);
Thread.Sleep(10);
WindowsMessageService.SendKey(key, KeyFlag.KeyUp);

Answer 1

Your first problem is that most games make use of DirectX input. You will have to make use of the following to send keys to the game. Also, you would need to send up and down key to simulate the keypress for the game.

[StructLayout(LayoutKind.Sequential)]
struct MouseInput
{
    public int dx;
    public int dy;
    public int mouseData;
    public int dwFlags;
    public int time;
    public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
struct KeyboardInput
{
    public short wVk;      //Virtual KeyCode (not needed here)
    public short wScan;    //Directx Keycode 
    public int dwFlags;    //This tells you what is use (Keyup, Keydown..)
    public int time;
    public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
struct HardwareInput
{
    public int uMsg;
    public short wParamL;
    public short wParamH;
}

[StructLayout(LayoutKind.Explicit)]
struct Input
{
    [FieldOffset(0)]
    public int type;
    [FieldOffset(4)]
    public MouseInput mi;
    [FieldOffset(4)]
    public KeyboardInput ki;
    [FieldOffset(4)]
    public HardwareInput hi;
}

[Flags]
public enum KeyFlag
{       
    KeyDown = 0x0000,
    ExtendedKey = 0x0001,
    KeyUp = 0x0002,
    UniCode = 0x0004,
    ScanCode = 0x0008
}

public static class WindowsMessageService
{
    [DllImport("user32.dll")]
    private static extern UInt32 SendInput(UInt32 nInputs,[MarshalAs(UnmanagedType.LPArray, SizeConst = 1)] Input[] pInputs, Int32 cbSize);

    public static void SendInput(short keycode, KeyFlag keyFlag)
    {
        var inputData = new Input[1];

        inputData[0].type = 1;
        inputData[0].ki.wScan = keycode;
        inputData[0].ki.dwFlags = (int)keyFlag;
        inputData[0].ki.time = 0;
        inputData[0].ki.dwExtraInfo = IntPtr.Zero;

        SendInput(1, inputData, Marshal.SizeOf(typeof(Input)));
    }

    public static void SendKey(short keyCode, KeyFlag keyFlag)
    {
        SendInput(keyCode, keyFlag | KeyFlag.ScanCode);
    }
}

Example of usage:

short key = 0x3B; // F1 key

WindowsMessageService.SendKey(key, KeyFlag.KeyDown);

Thread.Sleep(10);

WindowsMessageService.SendKey(key, KeyFlag.KeyUp);