I want to send keyboard input to a window in another process, without bringing that window to the foreground. I can use PostMessage
to fake the WM_KEYDOWN
and WM_KEYUP
; all I need to know is which window handle should receive the keyboard input -- i.e., something like GetFocus, but for another, non-active application.
The GetGUIThreadInfo API looks promising -- it returns an hwndFocus
for another app. But I've had no luck getting it to work from C# on my 64-bit OS. I've copied (and then further tweaked) the declarations from pinvoke.net, but all I ever get back is a generic error code (more details below).
I am setting cbSize before I call GetGUIThreadInfo, so I've avoided the most obvious potential problem.
I'm running 64-bit Vista, so I don't know whether the problem is that I'm not using the API correctly, or that it works differently in 64-bit -- I have yet to find a code sample that specifically says it works successfully in Win64.
Here's sample code. I'm using GetWindowThreadProcessId as recommended, so I don't think the problem has to do with mixing thread IDs with thread handles:
[StructLayout(LayoutKind.Sequential)] internal struct Rect { public int Left; public int Top; public int Right; public int Bottom; } [StructLayout(LayoutKind.Sequential)] internal class GuiThreadInfo { public int cbSize; public uint flags; public IntPtr hwndActive; public IntPtr hwndFocus; public IntPtr hwndCapture; public IntPtr hwndMenuOwner; public IntPtr hwndMoveSize; public IntPtr hwndCaret; public Rect rcCaret; } [DllImport("user32.dll")] internal static extern uint GetWindowThreadProcessId(IntPtr hWnd, IntPtr ProcessId); [DllImport("user32.dll", SetLastError = true)] internal static extern bool GetGUIThreadInfo(uint idThread, ref GuiThreadInfo lpgui); IntPtr GetFocusedHandleFromProcessWithWindow(IntPtr window) { var threadId = GetWindowThreadProcessId(window, IntPtr.Zero); var info = new GuiThreadInfo(); info.cbSize = Marshal.SizeOf(info); if (!GetGUIThreadInfo(threadId, ref info)) throw new Win32Exception(); return info.hwndFocus; }
window
is a valid window handle; GetWindowThreadProcessId
returns a nonzero thread handle. But the call to GetGUIThreadInfo
always returns false
, and the exception message is always "The parameter is incorrect".
Just in case the problem was that GetGUIThreadInfo
somehow doesn't have a 64-bit version, I tried changing all the 8-byte IntPtr
s in the GuiThreadInfo
declaration to 4-byte int
s, but I still got the same error.
Does anyone have a working C# sample of GetGUIThreadInfo
on Win64? Or, is there another way to find what the focused child-window handle would be in another app, without making that app active?
I haven't looked at it too closely but one thing jumps out. In your GetGUIThreadInfo call you pass the GUIThreadInfo structure by ref but you've defined it as a class so you are sending a reference by ref, in other words a pointer to a pointer. Either change your GUIThreadInfo to a struct or remove the ref on the parameter and add [In, Out] attributes.
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