Registering a custom win32 window class from c#
For the record I finally got this to work.Turned out the difficulties I had were down to string marshalling problems.I had to be more precise in my importing of win32 functions.
Below is the code that will create a custom window class in c# - useful for supporting old APIs you might have that rely on custom window classes.
It should work in either WPF or Winforms as long as a message pump is running on the thread.
EDIT:Updated to fix the reported crash due to early collection of the delegate that wraps the callback. The delegate is now held as a member and the delegate explicitly marshaled as a function pointer. This fixes the issue and makes it easier to understand the behaviour.
class CustomWindow : IDisposable{ delegate IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam); [System.Runtime.InteropServices.StructLayout( System.Runtime.InteropServices.LayoutKind.Sequential, CharSet = System.Runtime.InteropServices.CharSet.Unicode )] struct WNDCLASS { public uint style; public IntPtr lpfnWndProc; public int cbClsExtra; public int cbWndExtra; public IntPtr hInstance; public IntPtr hIcon; public IntPtr hCursor; public IntPtr hbrBackground; [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)] public string lpszMenuName; [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)] public string lpszClassName; } [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)] static extern System.UInt16 RegisterClassW( [System.Runtime.InteropServices.In] ref WNDCLASS lpWndClass ); [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)] static extern IntPtr CreateWindowExW( UInt32 dwExStyle, [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)] string lpClassName, [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)] string lpWindowName, UInt32 dwStyle, Int32 x, Int32 y, Int32 nWidth, Int32 nHeight, IntPtr hWndParent, IntPtr hMenu, IntPtr hInstance, IntPtr lpParam ); [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)] static extern System.IntPtr DefWindowProcW( IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam ); [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)] static extern bool DestroyWindow( IntPtr hWnd ); private const int ERROR_CLASS_ALREADY_EXISTS = 1410; private bool m_disposed; private IntPtr m_hwnd; public void Dispose() { Dispose(true); GC.SuppressFinalize(this); } private void Dispose(bool disposing) { if (!m_disposed) { if (disposing) { // Dispose managed resources } // Dispose unmanaged resources if (m_hwnd != IntPtr.Zero) { DestroyWindow(m_hwnd); m_hwnd = IntPtr.Zero; } } } public CustomWindow(string class_name){ if (class_name == null) throw new System.Exception("class_name is null"); if (class_name == String.Empty) throw new System.Exception("class_name is empty"); m_wnd_proc_delegate = CustomWndProc; // Create WNDCLASS WNDCLASS wind_class = new WNDCLASS(); wind_class.lpszClassName = class_name; wind_class.lpfnWndProc = System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegate(m_wnd_proc_delegate); UInt16 class_atom = RegisterClassW(ref wind_class); int last_error = System.Runtime.InteropServices.Marshal.GetLastWin32Error(); if (class_atom == 0 && last_error != ERROR_CLASS_ALREADY_EXISTS) { throw new System.Exception("Could not register window class"); } // Create window m_hwnd = CreateWindowExW( 0, class_name, String.Empty, 0, 0, 0, 0, 0, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero ); } private static IntPtr CustomWndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam) { return DefWindowProcW(hWnd, msg, wParam, lParam); } private WndProc m_wnd_proc_delegate;}
I'd like to comment the answer of morechilli:
public CustomWindow(string class_name){ if (class_name == null) throw new System.Exception("class_name is null"); if (class_name == String.Empty) throw new System.Exception("class_name is empty"); // Create WNDCLASS WNDCLASS wind_class = new WNDCLASS(); wind_class.lpszClassName = class_name; wind_class.lpfnWndProc = CustomWndProc; UInt16 class_atom = RegisterClassW(ref wind_class); int last_error = System.Runtime.InteropServices.Marshal.GetLastWin32Error(); if (class_atom == 0 && last_error != ERROR_CLASS_ALREADY_EXISTS) { throw new System.Exception("Could not register window class"); } // Create window m_hwnd = CreateWindowExW( 0, class_name, String.Empty, 0, 0, 0, 0, 0, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero );}In the constructor I copied above is slight error: The WNDCLASS instance is created, but not saved. It will eventually be garbage collected. But the WNDCLASS holds the WndProc delegate. This results in an error as soon as WNDCLASS is garbage collected. The instance of WNDCLASS should be hold in a member variable until the window is destroyed.
1) You can just subclass a normal Windows Forms class... no need for all those win32 calls, you just need to parse the WndProc message manually... is all.
2) You can import the System.Windows.Forms namespace and use it alongside WPF, I believe there won't be any problems as long as you don't intertwine too much windows forms into your WPF application. You just want to instantiate your custom hidden form to receieve a message is that right?
example of WndProc subclassing:
protected override void WndProc(ref System.Windows.Forms.Message m){ // *always* let the base class process the message base.WndProc(ref m); const int WM_NCHITTEST = 0x84; const int HTCAPTION = 2; const int HTCLIENT = 1; // if Windows is querying where the mouse is and the base form class said // it's on the client area, let's cheat and say it's on the title bar instead if ( m.Msg == WM_NCHITTEST && m.Result.ToInt32() == HTCLIENT ) m.Result = new IntPtr(HTCAPTION);}Since you already know RegisterClass and all those Win32 calls, I assume the WndProc message wouldn't be a problem for you...