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Detect active window changed using C# with a console application

This question is very similar to this one (Detect active window changed using C# without polling), and the code on that accepted answer works fine with a Windows Forms Application, but no way with a Console Application.
¿How can I detect that active window has changed without doing infinite iterations (or any type of polling) with a Console Application?
Thanks in advance.

It can be changed to run as a console application with a few changes. Here is a working code.
using System;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
dele = new WinEventDelegate(WinEventProc);
IntPtr m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, dele, 0, 0, WINEVENT_OUTOFCONTEXT);
Application.Run(); //<----
}
static WinEventDelegate dele = null; //STATIC
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;
[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);
private static string GetActiveWindowTitle() //STATIC
{
const int nChars = 256;
IntPtr handle = IntPtr.Zero;
StringBuilder Buff = new StringBuilder(nChars);
handle = GetForegroundWindow();
if (GetWindowText(handle, Buff, nChars) > 0)
{
return Buff.ToString();
}
return null;
}
public static void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) //STATIC
{
Console.WriteLine(GetActiveWindowTitle());
}
}
}

CreateWindowEx and RegisterClass C#

I want to create a new class and then show a window with the specefied class.
I wrote following codes for that :
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
[DllImport("user32.dll")]
static extern bool UpdateWindow(IntPtr hWnd);
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
[DllImport("user32.dll", SetLastError = true, EntryPoint = "CreateWindowEx")]
public static extern IntPtr CreateWindowEx(
int dwExStyle,
string lpClassName,
string lpWindowName,
int dwStyle,
int x,
int y,
int nWidth,
int nHeight,
IntPtr hWndParent,
IntPtr hMenu,
IntPtr hInstance,
IntPtr lpParam);
[System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
static extern System.UInt16 RegisterClassW(
[System.Runtime.InteropServices.In] ref WNDCLASSEX lpWndClass
);
struct WNDCLASSEX
{
[MarshalAs(UnmanagedType.U4)]
public int cbSize;
[MarshalAs(UnmanagedType.U4)]
public int style;
public IntPtr lpfnWndProc; // not WndProc
public int cbClsExtra;
public int cbWndExtra;
public IntPtr hInstance;
public IntPtr hIcon;
public IntPtr hCursor;
public IntPtr hbrBackground;
public string lpszMenuName;
public string lpszClassName;
public IntPtr hIconSm;
}
[DllImport("user32.dll")]
static extern IntPtr DefWindowProc(IntPtr hWnd, uint uMsg, IntPtr wParam, IntPtr lParam);
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
WNDCLASSEX wind_class = new WNDCLASSEX();
wind_class.cbSize = Marshal.SizeOf(typeof(WNDCLASSEX));
wind_class.style = 0x00020000;
wind_class.hbrBackground = (IntPtr) 5;
wind_class.cbClsExtra = 0;
wind_class.cbWndExtra = 0;
wind_class.hInstance = Marshal.GetHINSTANCE(GetType().Module);
wind_class.hIcon = this.Icon.Handle;
wind_class.hCursor = IntPtr.Zero;
wind_class.lpszMenuName = string.Empty;
wind_class.lpszClassName = "MyClass";
wind_class.lpfnWndProc = DefWindowProc(IntPtr.Zero, 0, IntPtr.Zero, IntPtr.Zero);
RegisterClassW(ref wind_class);
IntPtr lolo = CreateWindowEx(0, "MyClass", "MyClass",0,0,0,30,40,IntPtr.Zero,IntPtr.Zero,IntPtr.Zero,IntPtr.Zero);
ShowWindow(lolo, 1);
UpdateWindow(lolo);
}
}
}
But it isn't working correctly.
It doesn't show the window. when i search with Spy++ by my class name , It cant find any results..
I searched in web and do some edits in my code but they didn't work.
Where is my Problem !?
Regards.

Plain-vanilla Win32 is no fun from Win32 C, and it is much less fun from .NET. But anyway, it may be useful in rare cases. Here comes a C# class which should do what you want.
First, a general remarks on your software. In Win32, you should always check the return codes of the system calls, and in case of an error, call GetLastError() to get a more detailed information about the failure. If you had checked the result of the RegisterClass function and it failed, you would have known that it is useless to continue without having fixed that one.
The following is a class which may be used as template for further studies and which should successfully register and create a resizable window. Additionally some simple actions like doubleclick are processed in a custom Window procedure. For some parts of the code credit goes to this site being one of the very few I found in the web presenting something working.
The CreateWindowEx is tricky, because you must NOT put in a string as class name, but the result of the RegisterClassEx. The used constants are found mainly in the C-header file winuser.h. To be able to do something useful with this method, the main painting has to be done "by hand", being a cumbersome and tedious work by manipulationg Device Contexts properly. Of course, all this does not show up in the following example. The "create" method of the class may be called e.g. from a Windows Form button click. The namespace name is of course arbitrarily selected. The WinForm project is x86 32-bit, .NET 4.0.
Have fun!
namespace Win32FromForms
{
delegate IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);
class Win32Window
{
const UInt32 WS_OVERLAPPEDWINDOW = 0xcf0000;
const UInt32 WS_VISIBLE = 0x10000000;
const UInt32 CS_USEDEFAULT = 0x80000000;
const UInt32 CS_DBLCLKS = 8;
const UInt32 CS_VREDRAW = 1;
const UInt32 CS_HREDRAW = 2;
const UInt32 COLOR_WINDOW = 5;
const UInt32 COLOR_BACKGROUND = 1;
const UInt32 IDC_CROSS = 32515;
const UInt32 WM_DESTROY = 2;
const UInt32 WM_PAINT = 0x0f;
const UInt32 WM_LBUTTONUP = 0x0202;
const UInt32 WM_LBUTTONDBLCLK = 0x0203;
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
struct WNDCLASSEX
{
[MarshalAs(UnmanagedType.U4)]
public int cbSize;
[MarshalAs(UnmanagedType.U4)]
public int style;
public IntPtr lpfnWndProc;
public int cbClsExtra;
public int cbWndExtra;
public IntPtr hInstance;
public IntPtr hIcon;
public IntPtr hCursor;
public IntPtr hbrBackground;
public string lpszMenuName;
public string lpszClassName;
public IntPtr hIconSm;
}
private WndProc delegWndProc = myWndProc;
[DllImport("user32.dll")]
static extern bool UpdateWindow(IntPtr hWnd);
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
[System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
static extern bool DestroyWindow(IntPtr hWnd);
[DllImport("user32.dll", SetLastError = true, EntryPoint = "CreateWindowEx")]
public static extern IntPtr CreateWindowEx(
int dwExStyle,
UInt16 regResult,
//string lpClassName,
string lpWindowName,
UInt32 dwStyle,
int x,
int y,
int nWidth,
int nHeight,
IntPtr hWndParent,
IntPtr hMenu,
IntPtr hInstance,
IntPtr lpParam);
[DllImport("user32.dll", SetLastError = true, EntryPoint = "RegisterClassEx")]
static extern System.UInt16 RegisterClassEx([In] ref WNDCLASSEX lpWndClass);
[DllImport("kernel32.dll")]
static extern uint GetLastError();
[DllImport("user32.dll")]
static extern IntPtr DefWindowProc(IntPtr hWnd, uint uMsg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
static extern void PostQuitMessage(int nExitCode);
//[DllImport("user32.dll")]
//static extern sbyte GetMessage(out MSG lpMsg, IntPtr hWnd, uint wMsgFilterMin,
// uint wMsgFilterMax);
[DllImport("user32.dll")]
static extern IntPtr LoadCursor(IntPtr hInstance, int lpCursorName);
[DllImport("user32.dll")]
static extern bool TranslateMessage([In] ref MSG lpMsg);
[DllImport("user32.dll")]
static extern IntPtr DispatchMessage([In] ref MSG lpmsg);
internal bool create()
{
WNDCLASSEX wind_class = new WNDCLASSEX();
wind_class.cbSize = Marshal.SizeOf(typeof(WNDCLASSEX));
wind_class.style = (int)(CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS ) ; //Doubleclicks are active
wind_class.hbrBackground = (IntPtr) COLOR_BACKGROUND +1 ; //Black background, +1 is necessary
wind_class.cbClsExtra = 0;
wind_class.cbWndExtra = 0;
wind_class.hInstance = Marshal.GetHINSTANCE(this.GetType().Module); ;// alternative: Process.GetCurrentProcess().Handle;
wind_class.hIcon = IntPtr.Zero;
wind_class.hCursor = LoadCursor(IntPtr.Zero, (int)IDC_CROSS);// Crosshair cursor;
wind_class.lpszMenuName = null;
wind_class.lpszClassName = "myClass";
wind_class.lpfnWndProc = Marshal.GetFunctionPointerForDelegate(delegWndProc);
wind_class.hIconSm = IntPtr.Zero;
ushort regResult = RegisterClassEx(ref wind_class);
if (regResult == 0)
{
uint error = GetLastError();
return false;
}
string wndClass = wind_class.lpszClassName;
//The next line did NOT work with me! When searching the web, the reason seems to be unclear!
//It resulted in a zero hWnd, but GetLastError resulted in zero (i.e. no error) as well !!??)
//IntPtr hWnd = CreateWindowEx(0, wind_class.lpszClassName, "MyWnd", WS_OVERLAPPEDWINDOW | WS_VISIBLE, 0, 0, 30, 40, IntPtr.Zero, IntPtr.Zero, wind_class.hInstance, IntPtr.Zero);
//This version worked and resulted in a non-zero hWnd
IntPtr hWnd = CreateWindowEx(0, regResult, "Hello Win32", WS_OVERLAPPEDWINDOW | WS_VISIBLE, 0, 0, 300, 400, IntPtr.Zero, IntPtr.Zero, wind_class.hInstance, IntPtr.Zero);
if (hWnd == ((IntPtr)0))
{
uint error = GetLastError();
return false;
}
ShowWindow(hWnd, 1);
UpdateWindow(hWnd);
return true;
//The explicit message pump is not necessary, messages are obviously dispatched by the framework.
//However, if the while loop is implemented, the functions are called... Windows mysteries...
//MSG msg;
//while (GetMessage(out msg, IntPtr.Zero, 0, 0) != 0)
//{
// TranslateMessage(ref msg);
// DispatchMessage(ref msg);
//}
}
private static IntPtr myWndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
{
switch (msg)
{
// All GUI painting must be done here
case WM_PAINT:
break;
case WM_LBUTTONDBLCLK :
MessageBox.Show("Doubleclick");
break;
case WM_DESTROY:
DestroyWindow(hWnd);
//If you want to shutdown the application, call the next function instead of DestroyWindow
//PostQuitMessage(0);
break;
default:
break;
}
return DefWindowProc(hWnd, msg, wParam, lParam);
}
}
}

The problem is the marshaling of strings to LPStr, if you do it like this then the class name works:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
struct WNDCLASSEX
{
[MarshalAs(UnmanagedType.U4)]
public int cbSize;
[MarshalAs(UnmanagedType.U4)]
public int style;
public IntPtr lpfnWndProc;
public int cbClsExtra;
public int cbWndExtra;
public IntPtr hInstance;
public IntPtr hIcon;
public IntPtr hCursor;
public IntPtr hbrBackground;
[MarshalAs(UnmanagedType.LPStr)]
public string lpszMenuName;
[MarshalAs(UnmanagedType.LPStr)]
public string lpszClassName;
public IntPtr hIconSm;
}
[DllImport("user32.dll", SetLastError = true, EntryPoint = "CreateWindowEx")]
public static extern IntPtr CreateWindowEx(
int dwExStyle,
//UInt16 regResult,
[MarshalAs(UnmanagedType.LPStr)]
string lpClassName,
[MarshalAs(UnmanagedType.LPStr)]
string lpWindowName,
UInt32 dwStyle,
int x,
int y,
int nWidth,
int nHeight,
IntPtr hWndParent,
IntPtr hMenu,
IntPtr hInstance,
IntPtr lpParam);

Is there any event or way to detect when i change the active window on screen?

What i mean is for example i'm now watching the visual studio window then i click on the bottom on the Chrome icon and now i'm in the Chrome window .
I want it to detect that the window i'm in now is changed . Not if i clicked on the chrome icon or on the visual studio icon but to detect somehow that i changed the window i'm watching/active/using now .
For example this code :
In the top of my Form1 i added :
public delegate void ActiveWindowChangedHandler(object sender, String windowHeader, IntPtr hwnd);
public event ActiveWindowChangedHandler ActiveWindowChanged;
[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);
delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType,
IntPtr hwnd, int idObject, int idChild, uint dwEventThread,
uint dwmsEventTime);
const uint WINEVENT_OUTOFCONTEXT = 0;
const uint EVENT_SYSTEM_FOREGROUND = 3;
[DllImport("user32.dll")]
static extern bool UnhookWinEvent(IntPtr hWinEventHook);
[DllImport("user32.dll")]
static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax,
IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc,
uint idProcess, uint idThread, uint dwFlags);
IntPtr m_hhook;
private WinEventDelegate _winEventProc;
Then in the constructor :
_winEventProc = new WinEventDelegate(WinEventProc);
m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND,
EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, _winEventProc,
0, 0, WINEVENT_OUTOFCONTEXT);
Then added events and functions :
void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd,
int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
{
if (eventType == EVENT_SYSTEM_FOREGROUND)
{
if (ActiveWindowChanged != null)
ActiveWindowChanged(this,GetActiveWindowTitle(hwnd),hwnd);
}
}
private string GetActiveWindowTitle(IntPtr hwnd)
{
StringBuilder Buff = new StringBuilder(500);
GetWindowText(hwnd, Buff, Buff.Capacity);
return Buff.ToString();
}
~Form1()
{
UnhookWinEvent(m_hhook);
}
But i'm not sure how to get it work and how to use it and if it's the right code at all .
Could you show me please an example of a code how to do it ?

Yes, you can use SetWinEventHook function.
hEvent = SetWinEventHook(EVENT_SYSTEM_FOREGROUND ,
EVENT_SYSTEM_FOREGROUND , NULL,
WinEventProcCallback, 0, 0,
WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNPROCESS);
.......
VOID CALLBACK WinEventProcCallback ( HWINEVENTHOOK hWinEventHook, DWORD dwEvent, HWND hwnd, LONG idObject, LONG idChild, DWORD dwEventThread, DWORD dwmsEventTime)
{
/* your code here */
}
Quoted DReJ from here.

Windows Callback, When The Active Window Changed

public class ActiveWindow
{
public delegate void ActiveWindowChangedHandler(object sender, String windowHeader,IntPtr hwnd);
public event ActiveWindowChangedHandler ActiveWindowChanged;
[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);
delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType,
IntPtr hwnd, int idObject, int idChild, uint dwEventThread,
uint dwmsEventTime);
const uint WINEVENT_OUTOFCONTEXT = 0;
const uint EVENT_SYSTEM_FOREGROUND = 3;
[DllImport("user32.dll")]
static extern bool UnhookWinEvent(IntPtr hWinEventHook);
[DllImport("user32.dll")]
static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax,
IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc,
uint idProcess, uint idThread, uint dwFlags);
IntPtr m_hhook;
private WinEventDelegate _winEventProc;
public ActiveWindow()
{
_winEventProc = new WinEventDelegate(WinEventProc);
m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND,
EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, _winEventProc,
0, 0, WINEVENT_OUTOFCONTEXT);
}
void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd,
int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
{
if (eventType == EVENT_SYSTEM_FOREGROUND)
{
if (ActiveWindowChanged != null)
ActiveWindowChanged(this,GetActiveWindowTitle(hwnd),hwnd);
}
}
private string GetActiveWindowTitle(IntPtr hwnd)
{
StringBuilder Buff = new StringBuilder(500);
GetWindowText(hwnd, Buff, Buff.Capacity);
return Buff.ToString();
}
~ActiveWindow()
{
UnhookWinEvent(m_hhook);
}
}
when i switch between the active windows i get the callback
but when i maximize a minimized window i don't get a call back,
i find a work throw to solve this problem, but i am seeking for better solution
any help will be appreciated.

when i switch between the active windows i get the callback but when i maximize a minimized window i don't get a call back
Yes, you need to use either the EVENT_SYSTEM_MINIMIZESTART or EVENT_SYSTEM_MINIMIZEEND event constant to receive notification of window objects being minimized.
Use the eventMin and eventMax parameters of the SetWinEventHook function to indicate that you're interested in receiving notifications for one of these events and EVENT_SYSTEM_FOREGROUND.

CallbackOnCollectedDelegate at Application.Run(new Form1())

I made a very small application that captures the screen inside games using SlimDX.
(I press left click to capture)
The capture works (atleast when I click on the form itself) but as soon as I click on firefox or any other application, I get this exception :
A callback was made on a garbage collected delegate of type 'CaptureScreen!CaptureScreen.Form1+WinEventDelegate::Invoke'. This may cause application crashes, corruption and data loss. When passing delegates to unmanaged code, they must be kept alive by the managed application until it is guaranteed that they will never be called.
at this line in my program.cs:
Application.Run(new Form1());
My Form1.cs (the designer itself has no controls)
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;
using Microsoft.DirectX.Direct3D;
namespace CaptureScreen
{
public partial class Form1 : Form
{
private const uint WINEVENT_OUTOFCONTEXT = 0;
private const uint EVENT_SYSTEM_FOREGROUND = 3;
private const int WH_MOUSE_LL = 14;
private const int WM_LBUTTONDOWN = 513;
delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime);
IntPtr m_hhook;
[DllImport("user32.dll")]
static extern bool UnhookWinEvent(IntPtr hWinEventHook);
[DllImport("user32.dll")]
static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess, uint idThread, uint dwFlags);
[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);
public Form1()
{
m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, WinEventProc, 0, 0, WINEVENT_OUTOFCONTEXT);
hookProc = new HookProc(LowLevelMouseProc);
hook = SetWindowsHookEx(WH_MOUSE_LL, hookProc, GetModuleHandle(null), 0);
InitializeComponent();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
UnhookWinEvent(m_hhook);
UnhookWindowsHookEx(hook);
}
void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
{
if (eventType == EVENT_SYSTEM_FOREGROUND)
{
StringBuilder sb = new StringBuilder(500);
GetWindowText(hwnd, sb, sb.Capacity);
}
}
[DllImport("kernel32.dll")]
static extern IntPtr GetModuleHandle(string moduleName);
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);
[DllImport("user32.dll")]
public static extern int UnhookWindowsHookEx(IntPtr hhook);
[DllImport("user32.dll")]
static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, uint wParam, IntPtr lParam);
delegate IntPtr HookProc(int nCode, uint wParam, IntPtr lParam);
[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
public static extern IntPtr GetForegroundWindow();
private HookProc hookProc;
private IntPtr hook;
IntPtr LowLevelMouseProc(int nCode, uint wParam, IntPtr lParam)
{
if (nCode >= 0 && (IntPtr)wParam == (IntPtr)WM_LBUTTONDOWN)
{
CaptureScreen();
}
return CallNextHookEx(IntPtr.Zero, nCode, wParam, lParam);
}
private void CaptureScreen()
{
StreamReader reader = new StreamReader(Path.GetFullPath("../../Counter.txt"));
string currentpic = reader.ReadLine();
if (string.IsNullOrEmpty(currentpic))
currentpic = "0";
reader.Close();
Bitmap bitmap = Direct3DCapture.CaptureWindow(GetForegroundWindow());
bitmap.Save(Path.GetFullPath("../../ScreenCapture/Test" + currentpic + ".gif"), ImageFormat.Gif);
StreamWriter writer = new StreamWriter(Path.GetFullPath("../../Counter.txt"));
writer.Write((int.Parse(currentpic)) + 1);
writer.Close();
}
public readonly uint DWM_EC_DISABLECOMPOSITION = 0;
public readonly uint DWM_EC_ENABLECOMPOSITION = 1;
[DllImport("dwmapi.dll", EntryPoint = "DwmEnableComposition")]
protected static extern uint Win32DwmEnableComposition(uint uCompositionAction);
}
}
the class that captures the screen can be found here:
http://spazzarama.wordpress.com/2009/02/07/screencapture-with-direct3d/
Any idea on how I can fix this?

Your problem is that you are just passing WinEventProc to SetWinEventHook, which will implicitly create a delegate that is eligible to be GCed once the current method exits (if not sooner!) You are seeing the consequences of that fact.
You will need to create a new member of Form1 of type WinEventDelegate, and use that as the parameter:
private WinEventDelegate winEventProc;
and then make use of it in your call to SetWinEventHook:
this.winEventProc = new WinEventDelegate(WinEventProc);
m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, this.winEventProc, 0, 0, WINEVENT_OUTOFCONTEXT);
That should ensure that your delegate stays alive as long as you need.

I had this problem also and have a similar solution to #dlev already in place but it does not work. I found if you mark the member static, it prevents it from being collected.
private static WinEventDelegate winEventProc;

There is a MSDN link which may help you to solve your problem.
Let The CLR Find Bugs For You With Managed Debugging Assistants