WinEventHandler.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Framework / System / Windows / Documents / WinEventHandler.cs / 2 / WinEventHandler.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// 
// Description: WinEventHandler implementation. 
//
// History: 
//  02/04/2005 : [....] - created.
//
//---------------------------------------------------------------------------
 
using System;
using System.Collections; 
using System.Runtime.InteropServices; 
using System.ComponentModel;
using System.Diagnostics; 
using System.Security;
using System.Security.Permissions;
using System.Windows.Threading;
using MS.Win32; 

using MS.Internal; 
 
namespace System.Windows.Documents
{ 
    internal class WinEventHandler : IDisposable
    {
        //-----------------------------------------------------
        // 
        //  Constructors
        // 
        //----------------------------------------------------- 

        #region Constructors 

        // ctor that takes a range of events
        /// 
        /// Critical - as this calls the setter for _winEventProc.Value. 
        /// Safe - as this doesn't allow an arbitrary value to be set.
        ///  
        [SecurityCritical, SecurityTreatAsSafe] 
        internal WinEventHandler(int eventMin, int eventMax)
        { 
            _eventMin = eventMin;
            _eventMax = eventMax;

            _winEventProc.Value = new NativeMethods.WinEventProcDef(WinEventDefaultProc); 
            // Keep the garbage collector from moving things around
            _gchThis = GCHandle.Alloc(_winEventProc.Value); 
 
            // Workaround for bug 150666.
            Dispatcher dispatcher = Dispatcher.CurrentDispatcher; 
            if (dispatcher != null)
            {
                dispatcher.ShutdownFinished += new EventHandler(OnDispatcherShutDown);
            } 
        }
 
        ~WinEventHandler() 
        {
            Clear(); 
        }

        #endregion Constructors
 
        //------------------------------------------------------
        // 
        //  Internal Methods 
        //
        //----------------------------------------------------- 

        #region Internal Methods

        public void Dispose() 
        {
            // no need to call this finalizer. 
 
            GC.SuppressFinalize(this);
            Clear(); 
        }

        // callback for the class inherited from this.
        internal virtual void WinEventProc(int eventId, IntPtr hwnd) 
        {
        } 
 
        /// 
        ///     Critical: This code frees the gchandle and is critical because it calls GCHandle 
        ///     TreatAsSafe: Ok to call free on a handle that we have allocated
        /// 
        [SecurityCritical,SecurityTreatAsSafe]
        internal void Clear() 
        {
            // Make sure that the hooks is uninitialzied. 
            Stop(); 

            // free GC handle. 
            if (_gchThis.IsAllocated)
            {
                _gchThis.Free();
            } 
        }
 
        // install WinEvent hook and start getting the callback. 
        /// 
        /// Critical - as this calls SetWinEventHook which has a SUC on it and also calls 
        ///            the setter for _hHook.
        /// Safe - as this does not allow an arbitrary method to be set up as a hook and
        ///        also doesn't allow an aribtrary value to be set on _hHook.Value.
        ///  
        [SecurityCritical, SecurityTreatAsSafe]
        internal void Start() 
        { 
            if (_gchThis.IsAllocated)
            { 
                _hHook.Value = UnsafeNativeMethods.SetWinEventHook(_eventMin, _eventMax, IntPtr.Zero, _winEventProc.Value,
                                                             0, 0, NativeMethods.WINEVENT_OUTOFCONTEXT);
                if (_hHook.Value == IntPtr.Zero )
                { 
                    Stop();
                } 
            } 
        }
 
        // uninstall WinEvent hook.
        /// 
        /// Critical - as this calls UnhookWinEvent which has a SUC on it and also
        ///            calls the setter for _hHook.Value. 
        /// Safe - as this does not allow an arbitrary hook to be removed and sets
        ///        _hHook.Value to IntPtr.Zero which is safe. 
        ///  
        [SecurityCritical, SecurityTreatAsSafe]
        internal void Stop() 
        {
            if (_hHook.Value != IntPtr.Zero )
            {
                UnsafeNativeMethods.UnhookWinEvent(_hHook.Value); 
                _hHook.Value = IntPtr.Zero ;
            } 
        } 

        #endregion Internal Methods 

        //------------------------------------------------------
        //
        //  Private Methods 
        //
        //------------------------------------------------------ 
 
        #region Private Methods
 
        private void WinEventDefaultProc(int winEventHook, int eventId, IntPtr hwnd, int idObject, int idChild, int eventThread, int eventTime)
        {
            WinEventProc(eventId , hwnd);
        } 

        // Workaround for bug 150666. 
        private void OnDispatcherShutDown(object sender, EventArgs args) 
        {
            Stop(); 
        }

        #endregion Private Methods
 

        //----------------------------------------------------- 
        // 
        //  Private Fields
        // 
        //------------------------------------------------------

        #region Private Fields
 
        // min WinEvent.
        private int _eventMin; 
 
        // max WinEvent.
        private int _eventMax; 

        // hook handle
        private SecurityCriticalDataForSet _hHook;
 
        // the callback.
        private SecurityCriticalDataForSet _winEventProc; 
 
        // GCHandle to keep the garbage collector from moving things around
        private GCHandle _gchThis; 

        #endregion Private Fields
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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