asp.net控件开发基础(3)

缺乏、安全感 2022-05-27 13:21 158阅读 0赞

上次讲了在继承Control类的时候为什么需要重写Render方法  
  
本次来介绍控件的事件处理. 我们知道Button控件有OnClick事件,DropDownList控件有SelectedIndexChanged事件.  
  
一.回发事件和客户端回发  
  
下面来看一个最简单的例子  
  
按钮单击事件

1 protected  void  Button1\_Click( object  sender, EventArgs e)  
 2  \{  
 3  Label1.Text  =  " 你好:  " \+ TextBox1.Text;  
 4  \}

大家知道Web 服务器控件创建的按钮的类型有三种  
  
1.Button   
2.LinkButton  
3.ImageButton  
  
打开MSDN看到三个控件都继承 IPostBackEventHandler接口  
  
![ch1.jpg][]  
  
IPostBackEventHandler接口 专门定义了处理回发事件的方法,说白了就是onclick事件,如果自定义控件需要处理回发事件,你就需要继承 IPostBackEventHandler接口,然后实现接口的RaisePostBackEvent 方法,另外一个简单的方法就是直接继承Button控件就可以了.  
  
 **RaisePostBackEvent方法用于处理窗体发送给服务器时引发的事件,方法中有一个参数eventArgument 表示要传递到事件处理程序的可选事件参数的 String  
  
下面总结处理回发事件,必须要做的步骤  
  
(1)继承并**实现**IPostBackEventHandler接口的RaisePostBackEvent方法  
  
(2)为表单元素定义UniqueID,以与IPostBackEventHandler服务器控件的UniqueID相对应  
  
相应实现代码如下  
  
示例一**

![ExpandedBlockStart.gif][]  
![None.gif][] namespace  CustomControls  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] public  class  SuperButton1 : Control, IPostBackEventHandler  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] //  声明Click事件委托   
![InBlock.gif][]  public  event  EventHandler Click;  
![InBlock.gif][]  
![InBlock.gif][] //  定义OnClick事件处理程序   
![InBlock.gif][]  protected  virtual  void  OnClick(EventArgs e)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] if  (Click  !=  null )  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Click( this , e);  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] //  实现RaisePostBackEvent方法,处理回发事件   
![InBlock.gif][]  public  void  RaisePostBackEvent( string  eventArgument)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] OnClick(EventArgs.Empty);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] protected  override  void  Render(HtmlTextWriter output)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] output.Write( " <INPUT TYPE=submit name= "  \+  this .UniqueID  \+   
![InBlock.gif][] "  Value='确定' /> " );  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedBlockEnd.gif][]\}

如果你不熟悉委托的话,可以参考一篇叫 **一个** **C\#睡前故事** 的文章   
  
EventArgs.Empty表示没有事件数据的事件,不要跟我以前一样认为是一个空的事件,当时就很郁闷,干什么要触发空事件呢,都是因为没看清楚Empty字段的意思,以为就为空的意思了.  
  
EventArgs.Empty等同于 EventArgs类的构造函数,等同于new EventArgs()  
注意还在呈现控件的name属性加了UniqueID.  
好了,现在你可以测试下了.

1 ![None.gif][] protected  void  SuperButton1\_1\_Click( object  sender, EventArgs e)  
 2 ![ExpandedBlockStart.gif][] \{  
 3 ![InBlock.gif][] Label1.Text  =  " 你点击了此按钮 " ;  
 4 ![ExpandedBlockEnd.gif][] \}

这样你就成功定义了一个处理回发事件的控件. 假设你在页面上多次使用这个控件,编译器将为每个事件委托实例生成一个字段。如果事件的数目很大，则一个委托一个字段的存储成本可能无法接受。.所以推荐采用另外一种优化的事件实现  
  
EventHandlerList 类提供一个简单的委托列表来添加和删除委托,下面来看看更改后的代码,  
  
AddHandler有两个参数事件对象和添加的委托,在OnClick事件中必须显示将委托转换为EventHandler类型  
  
**示例二**

![ExpandedBlockStart.gif][]  
![None.gif][] using  System;  
![None.gif][] using  System.Web.UI;  
![None.gif][]  
![None.gif][] namespace  CustomComponents  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] public  class  SuperButton2 : Control, IPostBackEventHandler  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] //  声明Click事件委托   
![InBlock.gif][]  private  static  readonly  object  ClickKey  =  new  object ();  
![InBlock.gif][]  
![InBlock.gif][] public  event  EventHandler Click  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] add  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Events.AddHandler(ClickKey, value);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] remove  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Events.RemoveHandler(ClickKey, value);  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] //  定义OnClick事件处理程序   
![InBlock.gif][]  protected  virtual  void  OnClick(EventArgs e)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] EventHandler clickEventDelegate  =   
![InBlock.gif][] (EventHandler)Events\[ClickKey\];  
![InBlock.gif][] if  (clickEventDelegate  !=  null )  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] clickEventDelegate( this , e);  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] //  实现RaisePostBackEvent方法,处理回发事件   
![InBlock.gif][]  public  void  RaisePostBackEvent( string  eventArgument)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] OnClick( new  EventArgs());  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] protected  override  void  Render(HtmlTextWriter output)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] output.Write( " <INPUT TYPE=submit name= "  \+  this .UniqueID  \+   
![InBlock.gif][] "  Value='确定' /> " );  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedBlockEnd.gif][]\}

下面再来说下客户端回发事件,在HTML窗体元素中只有Button按钮和ImageButton才可以引起窗体回发.  
  
但如LinkButton链接按钮控件要希望启动回发的话,则要依赖客户端脚本的事件机制来实现其功能.  
  
在asp.net2.0中,button控件多了一个 UseSubmitBehavior 属性,指示 Button 控件使用客户端浏览器的提交机制(客户端回发)还是 ASP.NET 回发机制,默认采用回发机制,如果设置为false的话,则需要调用GetPostBackEventReference 方法来返回 Button 的客户端回发事件  
  
当设置UseSubmitBehavior 属性为flase时,你运行页面时,则会发现一段自动生成的javascript代码  
  
LinkButton也一样,再看下面例子,定义了枚举,定义button按钮和链接按钮,大家在测试的时候,打开源代码就会发现不同效果  
**示例三**

![ExpandedBlockStart.gif][]  
![None.gif][] using  System;  
![None.gif][] using  System.Web.UI;  
![None.gif][] using  System.Web.UI.WebControls;  
![None.gif][] using  System.ComponentModel;  
![None.gif][] namespace  CustomComponents  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] public  enum  ButtonDisplay  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Button  =  0 ,  
![InBlock.gif][] Hyperlink  =  1   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] \[ToolboxData( " <\{0\}:SuperButton3 runat=server></\{0\}:SuperButton3> " )\]  
![InBlock.gif][] public  class  SuperButton3 : Control, IPostBackEventHandler  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] public  virtual  ButtonDisplay Display  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] get   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] object  display  =  ViewState\[ " Display " \];  
![InBlock.gif][] if  (display  ==  null )  
![InBlock.gif][] return  ButtonDisplay.Button;  
![InBlock.gif][] else   
![InBlock.gif][] return  (ButtonDisplay)display;  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] set   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] ViewState\[ " Display " \]  =  value;  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] public  virtual  string  Text  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] get   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] object  text  =  ViewState\[ " Text " \];  
![InBlock.gif][] if  (text  ==  null )  
![InBlock.gif][] return  string .Empty;  
![InBlock.gif][] else   
![InBlock.gif][] return  ( string )text;  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] set   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] ViewState\[ " Text " \]  =  value;  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] private  static  readonly  object  ClickKey  =  new  object ();  
![InBlock.gif][]  
![InBlock.gif][] public  event  EventHandler Click  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] add  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Events.AddHandler(ClickKey, value);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] remove  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Events.RemoveHandler(ClickKey, value);  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] protected  virtual  void  OnClick(EventArgs e)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] EventHandler clickEventDelegate  =   
![InBlock.gif][] (EventHandler)Events\[ClickKey\];  
![InBlock.gif][] if  (clickEventDelegate  !=  null )  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] clickEventDelegate( this , e);  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] public  void  RaisePostBackEvent( string  argument)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][]  
![InBlock.gif][] OnClick(EventArgs.Empty);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] override  protected  void  Render(HtmlTextWriter writer)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] base .Render(writer);  
![InBlock.gif][] Page.VerifyRenderingInServerForm( this );  
![InBlock.gif][]  
![InBlock.gif][] if  (Display  ==  ButtonDisplay.Button)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] writer.Write( " <INPUT type=\\ " submit\\ "" );  
![InBlock.gif][] writer.Write( "  name=\\ ""  \+ this.UniqueID +  " \\ "" );  
![InBlock.gif][] writer.Write( "  id=\\ ""  \+ this.UniqueID +  " \\ "" );  
![InBlock.gif][] writer.Write( "  value=\\ ""  \+ Text +  " \\ "" );  
![InBlock.gif][] writer.Write( "  /> " );  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] else  if  (Display  ==  ButtonDisplay.Hyperlink)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] writer.Write( " <A href=\\ "" );   
![InBlock.gif][]  writer.Write(Page.GetPostBackClientHyperlink( this ,  "" ));  
![InBlock.gif][] writer.Write( " \\ " > "  \+ Text +  " </ A > " );   
![ExpandedSubBlockEnd.gif][]  \}   
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedBlockEnd.gif][]\}

如果大家本来就学过这方面的知识,看了心里还有谱,如果没有的话,里面有些方法不熟悉的话,还是要多看看MSDN. 说通俗点,回发事件可以就理解为 **按钮单击事件**,而按钮又分两种不同的回发事件方法,这样讲的话,更容易让人接受,而上面所讲的就是实现按钮单击事件实现的方法.  
  
**二.数据回发事件**  
  
好了,接着再讲 **数据回发**.跟上面讲的 **事件回发**有点不同.  
  
下面也举一个简单的例子,看下图,有两个DropDownList,一个开启AutoPostBack,一个没有开启,再接着看下面简单的代码,第一个DropDownList,改变下拉框值时,label没显示,按确定按钮后则显示label,第二个DropDownList改变下拉框值时就显示了label,因为开启了AutoPostBack.这个大家都明白吧.  
  
![ch2.jpg][]

![None.gif][]  protected  void  DropDownList1\_SelectedIndexChanged( object  sender, EventArgs e)  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] Label2.Text  =  " 你选择了:  "  \+  DropDownList1.SelectedItem.Text;  
![ExpandedBlockEnd.gif][] \}   
![None.gif][] protected  void  DropDownList2\_SelectedIndexChanged( object  sender, EventArgs e)  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] Label1.Text  =  " 你选择了:  "  \+  DropDownList2.SelectedItem.Text;  
![ExpandedBlockEnd.gif][] \}

以上实现的原理就是在SelectedIndexChanged事件里, 判断旧值和新值的比较 (比较数据),如果发生变化,则引发事件,数据回发就是实现这样的事件.再重新整理一下思路,明白何时会引发SelectedIndexChanged事件  
  
在选择下拉框值时,如果选的值跟原来的值相同,则不触发事件,如果选的值跟原来的值不同的话则触发SelectedIndexChanged事件(还是旧值和新值的比较).  
  
打开MSDN文档查看 DropDownList 类,则发现其继承了 **IPostBackDataHandler 接口,我的意思就是说想要实现Change这样的事件,就要继承其接口.看看MSDN对此接口的定义**  
  
IPostBackDataHandler 接口   
定义 ASP.NET 服务器控件为自动加载回发数据而必须实现的方法。  
  
LoadPostData 方法  根据服务器控件的状态由于回发而发生更改做出判断是否调用RaisePostDataChangedEvent 方法,返回true则调用(就是旧值和新值不同的时候)  
  
RaisePostDataChangedEvent 方法 用于引发任何更改事件  
  
以下的例子实现了如同textbox的TextChanged事件  
  
postDataKey表示控件内部数据的关键值,postCollection表示所有传入名称值的集合,其采用索引的方式来访问

![ExpandedBlockStart.gif][]  
![None.gif][]   
![None.gif][] using  System;  
![None.gif][] using  System.Web;  
![None.gif][] using  System.Web.UI;  
![None.gif][] using  System.Collections.Specialized;  
![None.gif][] using  System.ComponentModel;  
![None.gif][]  
![None.gif][] namespace  CustomComponents  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] \[ToolboxData( " <\{0\}:Textbox1 runat=server></\{0\}:Textbox1> " ),  
![InBlock.gif][] DefaultProperty( " Text " )\]  
![InBlock.gif][] public  class  Textbox1 : Control, IPostBackDataHandler  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] public  string  Text  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] get   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] object  text  =  ViewState\[ " Text " \];  
![InBlock.gif][] if  (text  ==  null )  
![InBlock.gif][] return  string .Empty;  
![InBlock.gif][] else   
![InBlock.gif][] return  ( string )text;  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][] set   
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] ViewState\[ " Text " \]  =  value;  
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] public  bool  LoadPostData( string  postDataKey,  
![InBlock.gif][] NameValueCollection postCollection)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] string  postedValue  =  postCollection\[postDataKey\];  
![InBlock.gif][] // 检查新旧数据   
![InBlock.gif][]  if  ( ! Text.Equals(postedValue))  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] Text  =  postedValue;  
![InBlock.gif][] return  true ;  
![InBlock.gif][] // 自动调用RaisePostDataChangedEvent()   
![ExpandedSubBlockEnd.gif][]  \}   
![InBlock.gif][] else   
![InBlock.gif][] return  false ;  
![InBlock.gif][] // 不发生变化   
![ExpandedSubBlockEnd.gif][]  \}   
![InBlock.gif][] public  void  RaisePostDataChangedEvent()  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] OnTextChanged(EventArgs.Empty);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] protected  virtual  void  OnTextChanged(EventArgs e)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] if  (TextChanged  !=  null )  
![InBlock.gif][] TextChanged( this , e);  
![ExpandedSubBlockEnd.gif][] \}   
![InBlock.gif][]  
![InBlock.gif][] public  event  EventHandler TextChanged;  
![InBlock.gif][]  
![InBlock.gif][] override  protected  void  Render(HtmlTextWriter writer)  
![ExpandedSubBlockStart.gif][] \{  
![InBlock.gif][] base .Render(writer);  
![InBlock.gif][] Page.VerifyRenderingInServerForm( this );  
![InBlock.gif][] writer.Write( " <INPUT type=\\ " text\\ "  name=\\ "" );   
![InBlock.gif][]  writer.Write( this .UniqueID);  
![InBlock.gif][] writer.Write( " \\ "  value = \\ ""  \+  this .Text  \+  " \\ "  /> " );   
![ExpandedSubBlockEnd.gif][]  \}   
![ExpandedSubBlockEnd.gif][] \}   
![ExpandedBlockEnd.gif][]\}   
![None.gif][]

上面实现的方法如同button的onclick事件,其实不然,而是通过回发数据的新旧数据进行判断,我在示例代码中加了另外一个例子,这里就不列出了,大家可以下载后再去看,看了就明白不是button的onclick事件了.  
  
本次主要讲了三个基础的事件处理  
  
(1)捕获回发事件  
(2)用于回调的客户端脚本  
(3)处理回发数据  
  
以下两个接口需要你慢慢的熟悉和使用  
  
**IPostBackEventHandler接口和IPostBackDataHandler 接口.**

想到Button按钮就要想到**IPostBackEventHandler接口,想要textbox,dropdownlist一些change事件则要想要****IPostBackDataHandler 接口,如果结合起来,再自己思考的话,会明白的更深刻.**  
  
可能很多地方我也没表达清楚,跟别人讲的很多重复了,但还要拿出来分享下,这样也可以提高自己.最后还望大家如果看到有什么错误,请指出.  
  
参考文章:  
  
[ASP.NET2.0服务器控件开发之实现事件][ASP.NET2.0]  
  
[ASP.NET2.0服务器控件之捕获回传事件][ASP.NET2.0 1]

[ASP.NET 2.0服务器控件之处理回传数据][ASP.NET 2.0]  
  
  
[本文示例代码下载][Link 1]

[ch1.jpg]: /images/20220527/c6bda317f32541f1aac89f0ee9fbbca1.png
[ExpandedBlockStart.gif]: /images/20220527/0760740890c44e568ea850d26ff87e8f.png
[None.gif]: /images/20220527/b9f376b5c71f418580f70dfd7c3b3968.png
[InBlock.gif]: /images/20220527/3aa146332d074cfaab10073de593345a.png
[ExpandedSubBlockStart.gif]: /images/20220527/0ab6c382c23a433782172192139cbe3e.png
[ExpandedSubBlockEnd.gif]: /images/20220527/5040fef22ad2448d8ae0f5e0ae7d4c3d.png
[ExpandedBlockEnd.gif]: /images/20220527/1dc8bec70b2b4c94b78dea3a5b606f45.png
[ch2.jpg]: /images/20220527/484bd8e2d15945aea72e1a9f486aa60c.png
[ASP.NET2.0]: http://dev.yesky.com/msdn/244/2482244.shtml
[ASP.NET2.0 1]: http://dev.yesky.com/msdn/491/2490491.shtml
[ASP.NET 2.0]: http://dev.yesky.com/msdn/452/2492452.shtml
[Link 1]: http://files.cnblogs.com/Clingingboy/ServerControl/Code3.rar