Passing HWND from Win32 to C#

Question

Hi Gents As great experts in COM Interop that u r I'd like to have your counsel on how to pass a Win32 window handler (HWND) to a C# dll. Would it be possible to use this handle in C# as a this-type object for the form (subclassed?) ? Many thanks!

Bechir Bejaoui · Answer

I see what you mean

Opariti · Answer

Neat implementation! I would propose you have the same vision and different approach (in fact that's what I'm missing!) This is the classic win32 implementation no need for COM interop mechanism. Isn't it another way to marshall hwnd to IntPtr (I even wonder if this is the right object see below) and backwards as per COM wrappers (without iDisposable)? What I want is to get access to the message execution of the unmanaged window via a normal .net synthax something like subclassing it in the background. As I initially said get the handle (or pick it up somewhow - that's easy) and wrapping it into an this object. As the handle is unique at the system level (in addition in this case the .net classes are just win32 wrappers) then I think we can find a straight way to hook the .net message pump (associated to the handles's instance) into the unmanaged window. The key here is to pass the hwnd into a this object (is an instance) via COM Interop not win32.

Bechir Bejaoui · Answer

I have fairly the same approach but with a little bit different vision Take a look on this code snippet and give me your mind interface IWindowHandler { void Close(int handle); void Dispose(); int GetForegroundWnd(); int GetWnd(int processID); void Maximize(int handle); void Minimize(int handle); void Normalize(int handle); } public sealed class WindowHandler:IDisposable IWindowHandler { /* I used the singleton design pattern within this * context because I remarqued that serveral instances * could lead to some unhandled troubles */ private WindowHandler(){} public static WindowHandler Activate() { return new WindowHandler(); } /* Those constant have to be used within the exported method from the unmanaged code */ private const int CLOSE_PARAM = 0x0010; private const int SHOWNORMAL_PARAM = 1; private const int SHOWMINIMIZED_PARAM = 2; private const int SHOWMAXIMIZED_PARAM = 3; //This function is used to send a message [DllImport(user32.dll)] private static extern int SendMessage(int hWnd int Msg int wParam int lParam); /* This function is very important because she returns the windows handler*/ [DllImport(user32.dll)] private static extern int GetForegroundWindow(); //This function shows the windows [DllImport(user32)] private static extern int ShowWindow(int hwnd int nCmdShow); /* This is also an important function as it chatches a given * window from a given access */ public Int32 GetWnd(int processID) { Process oProcess = Process.GetProcessById(processID); Int32 value = Convert.ToInt32(oProcess.MainWindowHandle); return value; } //This function gets the foreground of the window public Int32 GetForegroundWnd() { return GetForegroundWindow(); } //This method will close the window public void Close(Int32 handle) { SendMessage(handle CLOSE_PARAM 0 0); } /*This will show the minimized state of the *given windows*/ public void Minimize(Int32 handle) { ShowWindow(handle SHOWMINIMIZED_PARAM); } /*This will show the maximized state of the *given windows*/ public void Maximize(Int32 handle) { ShowWindow(handle SHOWMAXIMIZED_PARAM); } /*This will show the normal state of the *given windows*/ public void Normalize(Int32 handle) { ShowWindow(handle SHOWNORMAL_PARAM); } //This will dispose the object #region IDisposable Members public void Dispose() { GC.ReRegisterForFinalize(this); } #endregion }

Opariti · Answer

The scenario I have in mind is as following: create a window in unmanaged code - just to get the handle then I pass it to C# dll ( HWND type to IntPtr ?) then I use the pointer as a local this (.net) to add controls to the window why not having access to the message pump from the dll (either the one from unmanaged code or the one in the .net side). What do you think?

Bechir Bejaoui · Answer

Do you mean using a window handler as unmanaged entity from within C#?