当文本框TextChanged事件被解雇？ [英] When TextBox TextChanged event is fired?

问题描述

我的问题是：

正如我们所知道的ViewState是不负责存储和恢复的TextBox，CheckBox和控制等价值观。发生这通过的LoadPostData（）方法来实现IPostBackDataHandler界面控件完成的。

As we know ViewState is not responsible for storing and restoring TextBox,CheckBox and such controls Values. This is done by LoadPostData() method to controls that implement IPostBackDataHandler interface.

和我们也知道加载阶段之后，RaisePostBackEvent阶段，并提高相应的事件，例如按钮点击或者文本在TextBox改变，它的TextChanged事件将被解雇。

And we also know after Load stage,RaisePostBackEvent stage occurs and raise corresponding events such Button Click or if Text changed in a TextBox, its TextChanged event will be fired.

那么，如何系统的跟踪，如果ViewState是不负责和机制实际上触发文本框中的文本改变框TextChanged事件？

So how does system track the text changed if ViewState is not responsible for that and which mechanism actually fires TextBox TextChanged event ?

我其实在这一点上混淆。

I am actually confused at this point.

在此先感谢。

推荐答案

我觉得是这样工作的：

文本框因为它是由它的文本状态发射控件实现IPostBackDataHandler，而不是IPostBackEventHandler。因此，如果任何变化postedValue发生被确定

TextBox control implements IPostBackDataHandler instead of IPostBackEventHandler because it's fired by its text state. So if any changes happened in postedValue which is determined

if (presentValue == null || !presentValue.Equals(postedValue)) {
            Text = postedValue;
            return true;
         }

部分则返回true，并继续执行所以最后框TextChanged解雇。 。PFF混乱，但看起来很容易寿

portion then it returns true and keep executing so finally TextChanged fired. Pff confusing but looks easy tho.

using System;
using System.Web;
using System.Web.UI;
using System.Collections;
using System.Collections.Specialized;


namespace CustomWebFormsControls {

   [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")] 
   public class MyTextBox: Control, IPostBackDataHandler {


  public String Text {
     get {
        return (String) ViewState["Text"];
     }

     set {
        ViewState["Text"] = value;
     }
  }      


  public event EventHandler TextChanged;


  public virtual bool LoadPostData(string postDataKey, 
     NameValueCollection postCollection) {

     String presentValue = Text;
     String postedValue = postCollection[postDataKey];

     if (presentValue == null || !presentValue.Equals(postedValue)) {
        Text = postedValue;
        return true;
     }

     return false;
  }


  public virtual void RaisePostDataChangedEvent() {
     OnTextChanged(EventArgs.Empty);
  }


  protected virtual void OnTextChanged(EventArgs e) {
     if (TextChanged != null)
        TextChanged(this,e);
  }


  protected override void Render(HtmlTextWriter output) {
     output.Write("<INPUT type= text name = "+this.UniqueID
        + " value = " + this.Text + " >");
  }
   }   
}

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