C#和SendMessage(键)不起作用

我试图将密钥发送到应用程序.为了进行简单的测试，我只使用了记事本.代码就是这样的:

I tried to send a key to an application. For an easy test I just used notepad. That's what the code looks like:

[DllImport("USER32.DLL", EntryPoint = "SendMessageW", SetLastError = true,
         CharSet = CharSet.Unicode, ExactSpelling = true,
         CallingConvention = CallingConvention.StdCall)]
    public static extern bool SendMessage(IntPtr hwnd, int Msg, int wParam, int lParam);


        const int WM_KEYDOWN = 0x100;
    const int WM_a = 0x41;

        public void Press()
    {
        Process[] p = Process.GetProcessesByName("notepad");
        IntPtr pHandle = p[0].MainWindowHandle;

        SendMessage(pHandle, WM_KEYDOWN, WM_a, 0);
    }

但是什么也没发生.

我的主要目标是将密钥发送到提升的应用程序，但是我很乐意首先将其发送到记事本. 我想使用SendMessage，因为我想控制按下按钮的时间，也不想在前台使用其他应用程序.这就是我不使用SendKeys的原因.

My main goal is to send the key to an elevated application, but I would be happy to send it to notepad first. I want to work with SendMessage, because I want to control how long I press a button, also I don't want to have the other application in the foreground. That's the reason I am not working with SendKeys.