PostMessage到当前活动进程不适用于所有进程？

Question

I have this code:

    const UInt32 WM_KEYDOWN = 0x0100;

    const int VK_DOWN = 0x28;
    const int VK_UP = 0x26;

    [DllImport("user32.dll")]
    static extern bool PostMessage(IntPtr hWnd, UInt32 Msg, int wParam, int lParam);

    [DllImport("user32.dll")]
    private static extern IntPtr GetForegroundWindow();

    [DllImport("user32.dll")]
    private static extern Int32 GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

    private static Process GetProcessByHandle(IntPtr hwnd)
    {
        try
        {
            uint processID;
            GetWindowThreadProcessId(hwnd, out processID);
            return Process.GetProcessById((int)processID);
        }
        catch { return null; }
    }

    public static Process GetActiveProcess()
    {
        IntPtr hwnd = GetForegroundWindow();
        return hwnd != null ? GetProcessByHandle(hwnd) : null;
    }

    public static void KeyUp()
    {
        PostMessage(GetActiveProcess().MainWindowHandle, WM_KEYDOWN, VK_UP, 0);
    }

    public static void KeyDown()
    {
        PostMessage(GetActiveProcess().MainWindowHandle, WM_KEYDOWN, VK_DOWN, 0);
    }

When i call the KeyUp/KeyDown it works only on some process, proccess like text editos, visual studio.

But doesn't work on Explorer.exe, iTunes.exe, Chrome.exe, Outlook.exe, FileZilla.exe and more..

I ran debug on console:

    while (true)
    {
        Process currentProcess = GetActiveProcess();
        if (currentProcess != null)
            Console.WriteLine(currentProcess.MainWindowTitle);
        Thread.Sleep(1000);
    }

Here what I get from some applications:

ProjName - Microsoft Visual Studio (Administrator)
?PostMessage to Current Active Proccess doesn't work for all proccess ? - StackOverFlow - Google Chrome?
FileZilla
Inbox - Outlook Data File - Microsoft Outlook

And on Explorer.exe i get empty line..

Answer 1

There are multiple ways to read keyboard state in a Windows application, and responding to WM_KEYDOWN and WM_KEYUP is just one of them. Applications can also use GetKeyState or GetAsyncKeyState . Applications can also respond to the WM_CHAR , WM_SYSKEYDOWN and WM_SYSKEYUP messages. Different applications will use different methods and if you are not simulating the one the application is looking for, it won't respond.

The problem you are having is slightly different than the one posed in the question that Raymond linked to, but the solution may be the same. Namely using SendInput instead of PostMessage