EventCollection

如果在单个控件中有多个事件，那么使用System.ComponentModel.EventHandlerList对事件进行保存将会在内存占用上有不错的提高。EventHandlerList对一个类内发布多个事件提供了一个列表容器。下面是多个事件和使用EventHandlerList的对比示意:

 第一步是实例化一个EventHandlerList的实例：

protected EventHandlerList eventList = new EventHandlerList();

第二步是声明一个容器用于保存事件的key

private static readonly object ClickEvent = new object();

最后一步是像往常一样声明一个事件，但有所不同的是就像属性的get和set程序块一样，对于事件C#提供了add和remove关键字:

public event EventHandler Click

{

add

{

Events.AddHandler(ClickEvent, value);

}

remove

{

Events.RemoveHandler(ClickEvent, value);

}

}

而在这时的事件调用方法就会像下面代码：

protected virtual void OnClick(EventArgs e)

{

EventHandler clickEventDelegate = (EventHandler)Events[ClickEvent];

if (clickEventDelegate != null)

{

clickEventDelegate(this, e);

}

}

上面代码首先从事件列表中通过索引器以第一步中保存事件的key为参数提取出事件并检查客户端是否注册到此事件，如果是，则激发事件。

Command事件和事件冒泡

    Command事件是System.Web.UI.WebControls命名空间里的强大模式。这个最好的例子是GridView

在GridView的Row里嵌套的button点击会触发Command事件，后台可以根据CommandArgument的不同来决定是执行edit操作还是delete操作等。而事件冒泡有些像javascript里的事件冒泡，但有所不同的是这里的事件冒泡到能够处理这个事件的地方停止，比如上图中command事件会冒泡到DataGrid里的ItemCommand里停止，因为ItemCommand事件可以对command事件进行处理.

在定义Command事件时会和前面大同小异，不同之处在于首先需要一个继承与System.EventArgs的CommandEventArgs类来进行参数传递,代码如下

public class CommandEventArgs : EventArgs

{

public CommandEventArgs(string _commandName,string _commandArgument)

{

CommandName=_commandName;

CommandArgument=_commandArgument;

}

private string commandname;

private string commandArgument;

public virtual string CommandName

{

get

{

return commandname;

}

set

{

commandname = value;

}

}

public virtual string CommandArgument

{

get

{

return commandArgument;

}

set

{

commandArgument = value;

}

}

}

然后在需要定义的控件里定义这两个属性，代码如下:

public virtual string CommandName

{

get

{

object name = ViewState["CommandName"];

if (name == null)

return string.Empty;

else

return (string)name;

}

set

{

ViewState["CommandName"] = value;

}

}

public virtual string CommandArgument

{

get

{

object arg = ViewState["CommandArgument"];

if (arg == null)

return string.Empty;

else

return (string)arg;

}

set

{

ViewState["CommandArgument"] = value;

}

}

然后重复前面的步骤，在控件内部定义命令事件:

private static readonly object CommandKey = new object();

public event CommandEventHandler Command

{

add

{

Events.AddHandler(CommandKey, value);

}

remove

{

Events.RemoveHandler(CommandKey, value);

}

}

最后一步和前面说的引发事件的OnXXX的实现都略有不同，这里在控件内部实现的代码如下:

protected virtual void OnCommand(CommandEventArgs ce)

{

CommandEventHandler commandEventDelegate =(CommandEventHandler)Events[CommandKey];

if (commandEventDelegate != null)

{

commandEventDelegate(this, ce);

}

RaiseBubbleEvent(this, ce);

}

注意最后一句,RaiseBubbleEvent方法.这个方法可以将控件的事件传递到它的父容器上。

到这里很多人都会好奇，那CommandName和CommandArgument两个参数是如何传入到CommandEventArgs里去的呢？

其实是在引发事件时传入的,代码如下:

OnCommand(new CommandEventArgs(CommandName, CommandArgument));

DEMO 带Command事件的Button

    其实这个Demo就是把上面的代码全部拼装起来,代码可能会有点长，代码如下:

namespace DemoButton

{

[ToolboxData("<{0}:superbutton runat=server></{0}:superbutton>")]

public class ButtonDemo : Control, IPostBackEventHandler

{

public delegate void CommandEventHandler(object sender,CommandEventArgs e);

public virtual string Text

{

get

{

object text = ViewState["Text"];

if (text == null)

return string.Empty;

else

return (string)text;

}

set

{

ViewState["Text"] = value;

}

}

private static readonly object ClickKey = new object();

public event EventHandler Click

{

add

{

Events.AddHandler(ClickKey, value);

}

remove

{

Events.RemoveHandler(ClickKey, value);

}

}

protected virtual void OnClick(EventArgs e)

{

EventHandler clickEventDelegate = (EventHandler)Events[ClickKey];

if (clickEventDelegate != null)

{

clickEventDelegate(this, e);

}

}

private static readonly object CommandKey = new object();

public event CommandEventHandler Command

{

add

{

Events.AddHandler(CommandKey, value);

}

remove

{

Events.RemoveHandler(CommandKey, value);

}

}

public virtual string CommandName

{

get

{

object name = ViewState["CommandName"];

if (name == null)

return string.Empty;

else

return (string)name;

}

set

{

ViewState["CommandName"] = value;

}

}

public virtual string CommandArgument

{

get

{

object arg = ViewState["CommandArgument"];

if (arg == null)

return string.Empty;

else

return (string)arg;

}

set

{

ViewState["CommandArgument"] = value;

}

}

protected virtual void OnCommand(CommandEventArgs ce)

{

CommandEventHandler commandEventDelegate = (CommandEventHandler)Events[CommandKey];

if (commandEventDelegate != null)

{

commandEventDelegate(this, ce);

}

RaiseBubbleEvent(this, ce);

}

public void RaisePostBackEvent(string argument)

{

OnCommand(new CommandEventArgs(CommandName, CommandArgument));

//OnClick(EventArgs.Empty);

}

protected override void Render(HtmlTextWriter writer)

{

base.Render(writer);

Page.VerifyRenderingInServerForm(this);

writer.Write("<INPUT type=""submit""");

writer.Write(" name=""" + this.UniqueID + """");

writer.Write(" id=""" + this.UniqueID + """");

writer.Write(" value=""" + Text + """");

writer.Write(" />");

}

}

public class CommandEventArgs : EventArgs

{

public CommandEventArgs(string _commandName, string _commandArgument)

{

CommandName = _commandName;

CommandArgument = _commandArgument;

}

private string commandname;

private string commandArgument;

public virtual string CommandName

{

get

{

return commandname;

}

set

{

commandname = value;

}

}

public virtual string CommandArgument

{

get

{

return commandArgument;

}

set

{

commandArgument = value;

}

}

}

}

前台代码:

首先注册页面控件：

<%@ Register Namespace="DemoButton" TagPrefix="cc" %>

前台代码：

<cc:ButtonDemo runat="server" Text="第一个按钮" ID="bt1" CommandName="bt1"

CommandArgument="第一个button的参数" oncommand="bt1_Command" ></cc:ButtonDemo>

<cc:ButtonDemo runat="server" Text="第二个按钮" ID="bt2" CommandName="bt1"

CommandArgument="第二个button的参数" oncommand="bt1_Command" ></cc:ButtonDemo>

事件处理程序:

protected void bt1_Command(object sender, DemoButton.CommandEventArgs e)

{

if (e.CommandName == "bt1")

{

Response.Write("第一个button被点击了，参数是"+e.CommandArgument);

}

else if (e.CommandArgument == "bt12")

{

Response.Write("第二个button被点击了，参数是" + e.CommandArgument);

}

}

Demo的结果很简单，就不演示了:-)