WindowsMessageHook.cs

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using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
 
namespace ReLogic.OS.Windows;
 
internal class WindowsMessageHook : IDisposable
{
    private delegate IntPtr WndProcCallback(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
 
    private const int GWL_WNDPROC = -4;
 
    private IntPtr _windowHandle = IntPtr.Zero;
 
    private IntPtr _previousWndProc = IntPtr.Zero;
 
    private WndProcCallback _wndProc;
 
    private List<IMessageFilter> _filters = new List<IMessageFilter>();
 
    private bool disposedValue;
 
    public WindowsMessageHook(IntPtr windowHandle)
    {
        _windowHandle = windowHandle;
        _wndProc = WndProc;
        _previousWndProc = NativeMethods.SetWindowLongPtr(_windowHandle, -4, Marshal.GetFunctionPointerForDelegate((Delegate)_wndProc));
    }
 
    public void AddMessageFilter(IMessageFilter filter)
    {
        _filters.Add(filter);
    }
 
    public void RemoveMessageFilter(IMessageFilter filter)
    {
        _filters.Remove(filter);
    }
 
    private IntPtr WndProc(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam)
    {
        Message message = Message.Create(hWnd, msg, wParam, lParam);
        if (InternalWndProc(ref message))
        {
            return message.Result;
        }
        return NativeMethods.CallWindowProc(_previousWndProc, message.HWnd, message.Msg, message.WParam, message.LParam);
    }
 
    private bool InternalWndProc(ref Message message)
    {
        foreach (IMessageFilter filter in _filters)
        {
            if (filter.PreFilterMessage(ref message))
            {
                return true;
            }
        }
        return false;
    }
 
    protected virtual void Dispose(bool disposing)
    {
        if (!disposedValue)
        {
            NativeMethods.SetWindowLongPtr(_windowHandle, -4, _previousWndProc);
            disposedValue = true;
        }
    }
 
    ~WindowsMessageHook()
    {
        Dispose(disposing: false);
    }
 
    public void Dispose()
    {
        Dispose(disposing: true);
        GC.SuppressFinalize(this);
    }
}