UniqueEventHelper.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Core / System / Windows / Media / UniqueEventHelper.cs / 1 / UniqueEventHelper.cs
                        

                        
                            using System; 
using System.Collections;
using System.Diagnostics;

namespace System.Windows.Media 
{
    ///  
    /// Aids in making events unique. i.e. you register the same function for 
    /// the same event twice, but it will only be called once for each time
    /// the event is invoked. 
    ///
    /// UniqueEventHelper should only be accessed from the UI thread so that
    /// handlers that throw exceptions will crash the app, making the developer
    /// aware of the problem. 
    /// 
    internal class UniqueEventHelper 
            where TEventArgs : EventArgs 
    {
        ///  
        /// Add the handler to the list of handlers associated with this event.
        /// If the handler has already been added, we simply increment the ref
        /// count. That way if this same handler has already been added, it
        /// won't be invoked multiple times when the event is raised. 
        /// 
        internal void AddEvent(EventHandler handler) 
        { 
            if (handler == null)
            { 
                throw new System.ArgumentNullException("handler");
            }

            EnsureEventTable(); 

            if (_htDelegates[handler] == null) 
            { 
                _htDelegates.Add(handler, 1);
            } 
            else
            {
                int refCount = (int)_htDelegates[handler] + 1;
                _htDelegates[handler] = refCount; 
            }
        } 
 
        /// 
        /// Removed the handler from the list of handlers associated with this 
        /// event. If the handler has been added multiple times (more times than
        /// it has been removed), we simply decrement its ref count.
        /// 
        internal void RemoveEvent(EventHandler handler) 
        {
            if (handler == null) 
            { 
                throw new System.ArgumentNullException("handler");
            } 

            EnsureEventTable();

            if (_htDelegates[handler] != null) 
            {
                int refCount = (int)_htDelegates[handler]; 
 
                if (refCount == 1)
                { 
                    _htDelegates.Remove(handler);
                }
                else
                { 
                    _htDelegates[handler] = refCount - 1;
                } 
            } 
        }
 
        /// 
        /// Enumerates all the keys in the hashtable, which must be EventHandlers,
        /// and invokes them.
        ///  
        /// The sender for the callback.
        /// The args object to be sent by the delegate 
        internal void InvokeEvents(object sender, TEventArgs args) 
        {
            Debug.Assert((sender != null), "Sender is null"); 

            if (_htDelegates != null)
            {
                Hashtable htDelegates = (Hashtable)_htDelegates.Clone(); 
                foreach (EventHandler handler in htDelegates.Keys)
                { 
                    Debug.Assert((handler != null), "Event handler is null"); 
                    handler(sender, args);
                } 
            }
        }

        ///  
        /// Clones the event helper
        ///  
        internal UniqueEventHelper Clone() 
        {
            UniqueEventHelper ueh = new UniqueEventHelper(); 
            if (_htDelegates != null)
            {
                ueh._htDelegates = (Hashtable)_htDelegates.Clone();
            } 
            return ueh;
        } 
 
        /// 
        /// Ensures Hashtable is created so that event handlers can be added/removed 
        /// 
        private void EnsureEventTable()
        {
            if (_htDelegates == null) 
            {
                _htDelegates = new Hashtable(); 
            } 
        }
 
        private Hashtable _htDelegates;
    }

 

    // 
 

 
    internal class UniqueEventHelper
    {
        /// 
        /// Add the handler to the list of handlers associated with this event. 
        /// If the handler has already been added, we simply increment the ref
        /// count. That way if this same handler has already been added, it 
        /// won't be invoked multiple times when the event is raised. 
        /// 
        internal void AddEvent(EventHandler handler) 
        {
            if (handler == null)
            {
                throw new System.ArgumentNullException("handler"); 
            }
 
            EnsureEventTable(); 

            if (_htDelegates[handler] == null) 
            {
                _htDelegates.Add(handler, 1);
            }
            else 
            {
                int refCount = (int)_htDelegates[handler] + 1; 
                _htDelegates[handler] = refCount; 
            }
        } 

        /// 
        /// Removed the handler from the list of handlers associated with this
        /// event. If the handler has been added multiple times (more times than 
        /// it has been removed), we simply decrement its ref count.
        ///  
        internal void RemoveEvent(EventHandler handler) 
        {
            if (handler == null) 
            {
                throw new System.ArgumentNullException("handler");
            }
 
            EnsureEventTable();
 
            if (_htDelegates[handler] != null) 
            {
                int refCount = (int)_htDelegates[handler]; 

                if (refCount == 1)
                {
                    _htDelegates.Remove(handler); 
                }
                else 
                { 
                    _htDelegates[handler] = refCount - 1;
                } 
            }
        }

        ///  
        /// Enumerates all the keys in the hashtable, which must be EventHandlers,
        /// and invokes them. 
        ///  
        /// The sender for the callback.
        /// The args object to be sent by the delegate 
        internal void InvokeEvents(object sender, EventArgs args)
        {
            Debug.Assert((sender != null), "Sender is null");
 
            if (_htDelegates != null)
            { 
                Hashtable htDelegates = (Hashtable)_htDelegates.Clone(); 
                foreach (EventHandler handler in htDelegates.Keys)
                { 
                    Debug.Assert((handler != null), "Event handler is null");
                    handler(sender, args);
                }
            } 
        }
 
        ///  
        /// Clones the event helper
        ///  
        internal UniqueEventHelper Clone()
        {
            UniqueEventHelper ueh = new UniqueEventHelper();
            if (_htDelegates != null) 
            {
                ueh._htDelegates = (Hashtable)_htDelegates.Clone(); 
            } 
            return ueh;
        } 

        /// 
        /// Ensures Hashtable is created so that event handlers can be added/removed
        ///  
        private void EnsureEventTable()
        { 
            if (_htDelegates == null) 
            {
                _htDelegates = new Hashtable(); 
            }
        }

        private Hashtable _htDelegates; 
    }
} 

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

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