Problem capturing an event with an active window

Question

I am trying to capture the change event of the active Window. Let's say if a user is working on VS and he is switching to IE, I want to capture this event with an active window. I searched the Internet and found many examples, but nothing works for me.

This is the code that I have written so far, I'm not sure if this is not the case. I can not capture the necessary event through this

class Program { delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime); [DllImport("user32.dll")] static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess, uint idThread, uint dwFlags); private const uint WINEVENT_OUTOFCONTEXT = 0; private const uint EVENT_SYSTEM_FOREGROUND = 3; static void Main(string[] args) { WinEventDelegate dele = new WinEventDelegate(WinEventProc); IntPtr m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, dele, 0, 0, WINEVENT_OUTOFCONTEXT); Console.ReadKey(); } static void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) { Console.WriteLine("Something"); } } 

WinEventProc will never be called, can anyone determine what I am doing wrong programmatically or conceptually? I am using windows 7

Answer 1

You need to pump messages to receive WinEvents - and Console.ReadKey () will probably not. Try using the MessageBox for testing instead - and replace it with the appropriate message outline.

From MSDN :

Notes:
...
The client thread that calls SetWinEventHook must have a message loop in order to receive events

Answer 2

add ans event loop call it in void man I changed the code a bit and now it works fine .

 public class Program { delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime); [DllImport("user32.dll")] static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess, uint idThread, uint dwFlags); private const uint WINEVENT_OUTOFCONTEXT = 0; private const uint EVENT_SYSTEM_FOREGROUND = 3; static void Main(string[] args) { WinEventDelegate dele = new WinEventDelegate(WinEventProc); IntPtr m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, dele, 0, 0, WINEVENT_OUTOFCONTEXT); EventLoop.Run(); // Console.ReadKey(); } static void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) { Console.WriteLine(hwnd.ToString()); } } public static class EventLoop { public static void Run() { MSG msg; while (true) { if (PeekMessage(out msg, IntPtr.Zero, 0, 0, PM_REMOVE)) { if (msg.Message == WM_QUIT) break; TranslateMessage(ref msg); DispatchMessage(ref msg); } } } [StructLayout(LayoutKind.Sequential)] private struct MSG { public IntPtr Hwnd; public uint Message; public IntPtr WParam; public IntPtr LParam; public uint Time; } const uint PM_NOREMOVE = 0; const uint PM_REMOVE = 1; const uint WM_QUIT = 0x0012; [DllImport("user32.dll")] private static extern bool PeekMessage(out MSG lpMsg, IntPtr hwnd, uint wMsgFilterMin, uint wMsgFilterMax, uint wRemoveMsg); [DllImport("user32.dll")] private static extern bool TranslateMessage(ref MSG lpMsg); [DllImport("user32.dll")] private static extern IntPtr DispatchMessage(ref MSG lpMsg); } }e