Events: Custom Add and Remove : delegate Event « Language Basics « C# / C Sharp

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C# / C Sharp » Language Basics » delegate EventScreenshots 
Events: Custom Add and Remove
Events: Custom Add and Remove

/*
A Programmer's Introduction to C# (Second Edition)
by Eric Gunnerson

Publisher: Apress  L.P.
ISBN: 1-893115-62-3
*/

// 23 - Events\Custom Add and Remove
// copyright 2000 Eric Gunnerson
using System;
using System.Collections;
using System.Runtime.CompilerServices;


public class EventsCustomAddandRemove
{
    static public void ButtonHandler(object sender, EventArgs e)
    {
        Console.WriteLine("Button clicked");
    }
    
    public static void Main()
    {
        Button button = new Button();
        
        button.Click += new Button.ClickHandler(ButtonHandler);
        
        button.SimulateClick();
        
        button.Click -= new Button.ClickHandler(ButtonHandler);
        
        button.TearDown();
    }
}

//
// Global delegate cache. Uses a two-level hashtable. The delegateStore hashtable 
// stores a hashtable keyed on the object instance, and the instance hashtable is 
// keyed on the unique key. This allows fast tear-down of the object when it's destroyed.
//
public class DelegateCache
{
    private DelegateCache() {}    // nobody can create one of these
    
    Hashtable delegateStore = new Hashtable();    // top level hash table
    
    static DelegateCache dc = new DelegateCache();    // our single instance
    
    Hashtable GetInstanceHash(object instance)
    {
        Hashtable instanceHash = (HashtabledelegateStore[instance];
        
        if (instanceHash == null)
        {
            instanceHash = new Hashtable();
            delegateStore[instance= instanceHash;
            
        }
        return(instanceHash);
    }
    
    public static void Combine(Delegate myDelegate, object instance, object key)
    {
        lock(instance)
        {
            Hashtable instanceHash = dc.GetInstanceHash(instance);        
            
            instanceHash[key= Delegate.Combine((DelegateinstanceHash[key],
            myDelegate);
        }
    }
    
    public static void Remove(Delegate myDelegate, object instance, object key)
    {
        lock(instance)
        {
            Hashtable instanceHash = dc.GetInstanceHash(instance);        
            
            instanceHash[key= Delegate.Remove((DelegateinstanceHash[key],
            myDelegate);
        }
    }
    
    public static Delegate Fetch(object instance, object key)
    {
        Hashtable instanceHash = dc.GetInstanceHash(instance);        
        
        return((DelegateinstanceHash[key]);
    }
    
    public static void ClearDelegates(object instance)
    {
        dc.delegateStore.Remove(instance);
    }
}

public class Button
{
    public void TearDown()
    {
        DelegateCache.ClearDelegates(this);
    }
    
    
    public delegate void ClickHandler(object sender, EventArgs e);
    
    static object clickEventKey = new object();
    
    public event ClickHandler Click
    {
        add
        {
            DelegateCache.Combine(value, this, clickEventKey);
        }
        
        remove
        {
            DelegateCache.Remove(value, this, clickEventKey);
        }
    }
    
    protected void OnClick()
    {
        ClickHandler ch = (ClickHandlerDelegateCache.Fetch(this, clickEventKey);
        
        if (ch != null)
        ch(this, null);
    }
    
    public void SimulateClick()
    {
        OnClick();
    }
}

           
       
Related examples in the same category
1.A very simple event demonstrationA very simple event demonstration
2.An event multicast demonstrationAn event multicast demonstration
3.Individual objects receive notifications when instance event handlers are usedIndividual objects receive notifications when instance     event handlers are used
4.A class receives the notification when a static method is used as an event handlerA class receives the notification when      a static method is used as an event handler
5.Create a custom means of managing the event invocation listCreate a custom means of managing the event invocation list
6.Use the bult-in EventHandler delegateUse the bult-in EventHandler delegate
7.Use delegate: eventUse delegate: event
8.Delegate and event hierarchyDelegate and event hierarchy
9.Events:Add and Remove FunctionsEvents:Add and Remove Functions
10.Events:Add and Remove Functions 2Events:Add and Remove Functions 2
11.Delegates And EventsDelegates And Events
12.Delegates And Events 2Delegates And Events 2
13.Chaining events.
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