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);
}
}
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