EventHandlerList

最新推荐文章于 2022-04-21 17:17:29 发布

转载最新推荐文章于 2022-04-21 17:17:29 发布 · 88 阅读

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原文链接：http://www.cnblogs.com/kasafuma/archive/2011/04/07/2008204.html

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#数据结构与算法

本文介绍了一个用于管理事件处理程序的类EventHandlerList。该类通过内部维护的链表管理各种类型的事件处理器，支持添加、移除及查找事件处理器等功能。文章通过具体示例展示了如何使用此类进行事件的注册与触发。

public sealed class EventHandlerList : IDisposable
{
    // Fields
    private ListEntry head;
    private Component parent;

    // Methods
    public EventHandlerList();
    internal EventHandlerList(Component parent)
    {
            this.parent = parent;
    }

public void AddHandlers(EventHandlerList listToAddFrom)
{
    for (ListEntry entry = listToAddFrom.head; entry != null; entry = entry.next)
    {
        this.AddHandler(entry.key, entry.handler);
    }
}

private ListEntry Find(object key)
{
    ListEntry head = this.head;
    while (head != null)
    {
        if (head.key == key)
        {
            return head;  这里使用递归找到这种委托类型的 ListEntry
        }
        head = head.next;
    }
    return head;
}

public void RemoveHandler(object key, Delegate value)
{
    ListEntry entry = this.Find(key);
    if (entry != null)
    {
        entry.handler = Delegate.Remove(entry.handler, value);
    }
}
    // Properties

public Delegate this[object key]
{
    get
    {
        ListEntry entry = null;
        if ((this.parent == null) || this.parent.CanRaiseEventsInternal)
        {
            entry = this.Find(key);
        }
        if (entry != null)
        {
            return entry.handler; //等于这种委托类型的委托,有可能是个handler链表
        }
        return null;
    }
    set
    {
        ListEntry entry = this.Find(key);
        if (entry != null)
        {
            entry.handler = value;
        }
        else
        {
            this.head = new ListEntry(key, value, this.head);
        }
    }
}

public void AddHandler(object key, Delegate value)
{
    ListEntry entry = this.Find(key);
    if (entry != null)
    {
        entry.handler = Delegate.Combine(entry.handler, value); //如果已经在链表中注册过这种类别的委托,则找到并且把新添加的委托实例加入进去
    }
    else
    {
        this.head = new ListEntry(key, value, this.head);//如果还没有在链表中注册过这种类别的委托,则添加到链表中
    }
}

Dkey2 | DKey1

D2DosomthingList | D1DosomthingList

next | next

D2的next指向后面的整个对象,D1的next为null

    // Nested Types
    private sealed class ListEntry
    {
        // Fields
        internal Delegate handler;
        internal object key;
        internal EventHandlerList.ListEntry next;

        // Methods
       public ListEntry(object key, Delegate handler, EventHandlerList.ListEntry next)
    {
            this.next = next;
            this.key = key;
            this.handler = handler;
    }

    }
}

举例:

public event EventHandler DateChanged
        {
            add
            {
                base.Events.AddHandler(DateChangedEvent, value);
            }
            remove
            {
                base.Events.RemoveHandler(DateChangedEvent, value);
            }
        }

protected void OnDateChanged(EventArgs e)
        {
            if (base.Events != null)
            {
                EventHandler handler1 = (EventHandler)base.Events[DateChangedEvent];
                if (handler1 != null)
                {
                    handler1(this, e);
                }
            }
        }

private static readonly object DateChangedEvent;

DateChangedEvent = new object();

转载于:https://www.cnblogs.com/kasafuma/archive/2011/04/07/2008204.html