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I am trying to do one of the following 1. open desired program and press a key programmatically 2. find open window of program and press a key programmatically (either is fine)

I have tried numerous implementations of SendKeys.SendWait(), PostMessage(), and SendMessage() unsuccessfully. Below are my code snippets

 //included all these for attempts [DllImport("User32.dll")] static extern IntPtr FindWindow(string lpClassName, string lpWindowName); [DllImport("User32.dll")] static extern int SetForegroundWindow(IntPtr hWnd); [DllImport("User32.Dll", EntryPoint = "PostMessageA")] static extern bool PostMessage(IntPtr hWnd, uint msg, int wParam, int lParam); [DllImport("user32.dll")] static extern byte VkKeyScan(char ch); [DllImport("user32.dll", CharSet = CharSet.Auto)] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

Get handle of window, variables used by sendmessage/postmessage/sendkeys

IntPtr ptrOBS = proc.Handle;//this works properly, proc is instantiated properly //IntPtr ptrOBS = FindWindow(null, "Open Broadcaster Software v0.472b"); SetForegroundWindow(ptrOBS); const UInt32 WM_CHAR = 0x0102; const uint WM_KEYDOWN = 0x100; const int VK_R = 0x52; // taken from http://msdn.microsoft.com/en-us/library/dd375731(v=vs.85).aspx const int VK_S = 0x53;

SendMessage attempt:

SendMessage(ptrOBS, WM_KEYDOWN, (IntPtr)VK_R, (IntPtr)1);//tried both WM_CHAR and WM_KEYDOWN

PostMessage attempt:

string message = "rs"; bool sent = PostMessage(ptrOBS, WM_KEYDOWN, VkKeyScan(message[0]), 0);

SendKeys attempt:

SendKeys.SendWait("{r}");

Tried SetFocus on the parent window (application) and child window (button triggered by keypress im trying to send):

static void SetFocus(IntPtr hwndTarget, string childClassName) { // hwndTarget is the other app's main window // ... IntPtr targetThreadID = GetWindowThreadProcessId(hwndTarget, IntPtr.Zero); //target thread id IntPtr myThreadID = GetCurrentThread(); // calling thread id, our thread id try { bool lRet = AttachThreadInput(myThreadID, targetThreadID, -1); // attach current thread id to target window // if it's not already in the foreground... lRet = BringWindowToTop(hwndTarget); SetForegroundWindow(hwndTarget); // if you know the child win class name do something like this (enumerate windows using Win API again)... IntPtr hwndChild = (IntPtr)1183492;//(IntPtr)EnumAllWindows(hwndTarget, childClassName).FirstOrDefault(); if (hwndChild == IntPtr.Zero) { // or use keyboard etc. to focus, i.e. send keys/input... // SendInput (...); return; } // you can use also the edit control's hwnd or some child window (of target) here SetFocus(hwndChild); // hwndTarget); SendKeys.SendWait("{r}"); } finally { SendKeys.SendWait("{r}"); bool lRet = AttachThreadInput(myThreadID, targetThreadID, 0); //detach from foreground window SendKeys.SendWait("{r}"); } }

For NSGaga:

 string windowName = "Open Broadcaster Software v0.472b"; IntPtr outerPtr = FindWindow(null, windowName); IntPtr ptrOBS = (IntPtr)527814;//button that im trying to trigger keypress on SetForegroundWindow(outerPtr); SetForegroundWindow(ptrOBS); SetFocus(outerPtr, "OBSWindowClass");//SetFocus(ptrOBS, "Button"); const UInt32 WM_CHAR = 0x0102; const int VK_R = 0x52; // taken from http://msdn.microsoft.com/en-us/library/dd375731(v=vs.85).aspx const int VK_S = 0x53; //SetForegroundWindow(ptrOBS); System.Threading.Thread.Sleep(3000); SendKeys.SendWait("{r}"); SendMessage(outerPtr, WM_KEYDOWN, (IntPtr)VK_R, (IntPtr)1); PostMessage(outerPtr, WM_KEYDOWN, VkKeyScan('r'), 0);
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  • Is the target process elevated? Commented Mar 20, 2013 at 23:53
  • heh i would have punched the wall if that was the case, didnt make a difference. Commented Mar 21, 2013 at 0:26
  • See: stackoverflow.com/questions/4944621/… Commented Mar 21, 2013 at 0:48

2 Answers 2

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You cannot reliably use SendMessage and PostMessage for synthesizing keyboard input. They are just not designed for this. These messages (WM_CHAR, WM_KEYDOWN, etc.) are notifications raised by lower-level subsystems when keyboard input has been received, processed, and forwarded on to the appropriate recipient. Sending or posting these messages yourself is like prank-calling someone.

SendKeys (like all other input synthesizer methods, including the SendInput function which was explicitly designed for synthesizing keyboard input and in at least some implementation is what SendKeys actually uses under the hood) works only when the window you wish to receive the keyboard input has the focus. In Windows, only focused (active) windows receive input events.

So SendKeys is probably the way to go if you're ever going to get this to work (either that or P/Invoking SendInput and all of its associated structures), but you do need to respect the caveat that the recipient window must have the focus. Otherwise, it's not going to get anything.

It looks like from your sample code that you're trying to use the SetForegroundWindow function to meet this precondition. Unfortunately, you're passing it an invalid value, and not doing any error checking that might alert you to this mistake. Specifically, this code is wrong:

IntPtr ptrOBS = proc.Handle;//this works properly, proc is instantiated properly SetForegroundWindow(ptrOBS); // WRONG, ptrOBS is not a window handle

Even if I trust you on ptrOBS being initialized correctly, that makes it a valid handle to a process, which is a very different thing than a valid handle to a window. Aside from the obvious nominal differences, processes can have multiple windows and only a single window can have the focus (i.e., be "in the foreground").

You will need to obtain the handle to a particular window before calling SetForegroundWindow, and given that we know a process can have multiple windows, that can be tricky. You need some reliable way of determining which window you want. Lots of people accomplish this by hard-coding the name of the window as a string, which works great until the target app is recompiled and this implementation detail changes. The only bulletproof way that I can think of is to have the user click the target window and your code to retrieve the handle of the window that is currently under the mouse pointer.

And of course all of this assumes that you've observed the restrictions on the use of SetForegroundWindow, enumerated in the "Remarks" section of the linked SDK documentation.

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3 Comments

IntPtr ptrOBS = FindWindow(null, "Open Broadcaster Software v0.472b"); doesn't work either, and im assuming FindWindow does return the actual window handle, not the process handle? But thank you for pointing out the things i need to be looking at and changing. I will now keep hammering at the SendKeys method with a real window handle.
@AHeinen Have you verified that FindWindow actually returns a handle? The correct handle? Use Spy++ to verify this by comparing it to the actual handle of the window you're interested in.
it does return the actual parent window of the application. I also tried hardcoding the IntPtr hex=>decimal value for the child window housing the action i want to run with keypress (the button that hotkey presses). using either/both windows didn't work. I tried implementing SetFocus (will update OP with my attempt)
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There is lot of trial and error with that, to get it working
Here is a bit of code I posted before, you might wanna give a try (and there is some more info attached)...

Pinvoke SetFocus to a particular control

Try setting focus first (using the mechanism mentioned) - and then using SendKeys or SendInput.

Here is some detailed code for SendInput...

How to send a string to other application including Microsoft Word

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9 Comments

did you manage to SetFocus on anything in the target window - using what I proposed (that has to be followed to the letter) - that's the first step. I had that working many times over. However, some apps are specific. Also try elevating your app (as admin) if it helps.
or try posting your final code you have made (with that approach) - I'll copy paste and run here (adjust) and try to take a look if time allows
setfocus implementation i tried was above; do you want me to post my win32 api function declarations or just calling setfocus then sendkeys?
best full repro (just cut down to min - e.g. try with notepad or something) - that's easiest to work with (common sample)
I see :) I'll take a look for sure (when I find some time, later on or tomorrow) - tell me just did you try on any other program - like w/ Notepad I mentioned? I think you're doing something wrong with keys sending - that's a tricky part
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