C # Hook in-thread message interception

The hook is actually a call to the API:

1, install Hook:
SetWindowsHookEx
Function prototype: Hhook SetWindowsHookEx (
int Idhook,//hook type,
HookProc LPFN,//hook function address
INSTANCE Hmod,//The handle of the instance where the hook is located,
The thread number of the thread that the DWORD dwthreadid//Hook is monitoring
)
Hmod: For the thread procedure hook, the parameter passes null;
For system hooks: a handle to a hook DLL with a parameter
dwThreadID: For global hooks, this parameter is null.
Hook type with wh_callwndproc=4 (message sent to window). triggered by SendMessage)
Return: Success: Return SetWindowsHookEx to return the installed hook handle;
Failure: NULL;

2, callback, you want to intercept the message is carried out here:
LRESULT WINAPI Myhookproc (
int ncode,//Specify whether the message needs to be processed
WPARAM WPARAM,//contains additional messages for this message
LPARAM LPARAM//contains additional messages for this message
)

3. Call the next hook
Lresult CallNextHookEx (
Hhook HHK,//is the handle to your own hook function. Use this handle to traverse the hook chain
int ncode,//pass the incoming parameters simply to CallNextHookEx
WPARAM WPARAM,//pass the incoming parameters simply to CallNextHookEx
LPARAM LPARAM//Pass the incoming parameters simply to CallNextHookEx
);

4, after use, remember to uninstall the hook Oh, otherwise your system will become very slow incomparable!
BOOL UnhookWindowsHookEx (
Hhook HHK//hook handle to uninstall.
)

Use the above APIs in C # to encapsulate it, you can use it directly!
Give an example of a thread hook (two form runs on the same thread):

Using System.Runtime.InteropServices;

public class Form1:System.Windows.Forms.Form
{
...
Define delegate (Hook function, for callback)
public delegate int HookProc (int code, INTPTR wparam, ref cwpstruct CWP);

function to install hooks
[DllImport ("User32.dll", CharSet = CharSet.Auto)]
public static extern IntPtr SetWindowsHookEx (int type, HookProc hook, IntPtr instance, int ThreadID);
function to call next hook
[DllImport ("User32.dll", CharSet = CharSet.Auto)]
public static extern int CallNextHookEx (IntPtr hookhandle, int code, INTPTR wparam, ref cwpstruct CWP);
Uninstall Hook
[DllImport ("User32.dll", CharSet = CharSet.Auto)]
public static extern bool UnhookWindowsHookEx (IntPtr hookhandle);
Get form Thread ID
DllImport ("User32.dll", CharSet = CharSet.Auto)]
public static extern int GetWindowThreadProcessId (INTPTR hwnd, int ID);

Private HookProc HookProc;
Private IntPtr hookhandle = IntPtr.Zero;

Public Form1 ()
{
....
Hook handling method
This.hookproc = new HookProc (MYHOOKPROC);
}

Start intercept.
private bool Starthook ()
{
Form2 f=new Form2 ();
F.show ()//plus this
Install hooks to intercept messages sent to Form2 by the system
This.hookhandle = SetWindowsHookEx (4, HookProc, IntPtr.Zero, GetWindowThreadProcessId (f.handle,0));
Return (this.hookhandle!= 0);
}


Stop Intercept
private bool Stophook ()
{
return UnhookWindowsHookEx (This.hookhandle);
}

Hook handler function, intercept the message here and do the processing
private int Myhookproc (int code, INTPTR wparam, ref cwpstruct CWP)
{
Switch (code)
{
Case 0:
Switch (cwp.message)
{
Case 0x0000f://wm_paint, intercept WM_PAINT message
Do something
Break
}
Break
}
Return CallNextHookEx (Hookhandle,code,wparam, ref CWP);
}

[StructLayout (LayoutKind.Sequential)]
public struct CWPSTRUCT
{
public INTPTR lparam;
Public INTPTR wparam;
public int message;
Public INTPTR hwnd;
}
}

public class Form2:System.Windows.Forms.Form
{
....
}