Send emulated events to another window

I send mouse events to another application in the following way. The problem is, this works for some applications but not for others. Why?

using System.Runtime.InteropServices;
using System.Diagnostics;



namespace WpfApplication1
{

  public partial class MainWindow : Window
  {


    [DllImport("user32.dll")]
    private static extern int SendMessage(IntPtr h开发者_如何学JAVAWnd, uint Msg, IntPtr wParam, IntPtr lParam);


    private const int downclick = 0x201;
    private const int upclick = 0x202;
    IntPtr handle = IntPtr.Zero;

    public MainWindow()
    {
      InitializeComponent();
    }

    private void button1_Click(object sender, RoutedEventArgs e)
    {
      foreach (Process p in Process.GetProcessesByName("mspaint"))
      {
        IntPtr handle = p.MainWindowHandle;
        int X = 50;
        int Y = 380;
        IntPtr lParam = (IntPtr)((Y << 16) | X);
        IntPtr wParam = IntPtr.Zero;
        SendMessage(handle, downclick, wParam, lParam);
        SendMessage(handle, upclick, wParam, lParam);
      }  
    } 
  }
}

Using Spy++ I see that the application recieves the following data:

<00062> 0004052C S WM_LBUTTONDOWN fwKeys:0000 xPos:50 yPos:380
<00063> 0004052C R WM_LBUTTONDOWN
<00064> 0004052C S WM_LBUTTONUP fwKeys:0000 xPos:50 yPos:380
<00065> 0004052C R WM_LBUTTONUP

I assume that the events themselves are correct. But I don't know why it works for some software but not for others. How can I send mouse messages from one window to another? The software where I want to send the messages is not always visible.

Is it possible at all?

No it's not possible in any reliable way - as you've found out in your testing. The mouse messages are only one part of the input. Windows keeps an input state and just sending messages will not update that input state. And you're also ignoring mouse move messages, etc.

For example in your WinForms application you can use the MousePosition property to get the current mouse positon. Sending messages can't simulate that.

Also you can't send the mouse message to the main window handle, you would have to find the exact button you want to click on and send the message directly to the correct button.

So maybe it will work if the application is only listening for mouse messages this will work, but if not they it won't.

They supported way to simulate mouse clicks, is the SendInput function. But that won't work with minimized applications. It literally goes through the entire Windows input process and will move the mouse cursor - which means that the application has to be visible on the screen.

Here's some information, it talks about keyboard events, but similar logic applies: http://blogs.msdn.com/b/oldnewthing/archive/2005/05/30/423202.aspx http://blogs.msdn.com/b/oldnewthing/archive/2010/12/21/10107494.aspx