問題有關asp.net事件處理

Question

是什麼

<asp:DropDownList ID="Combo" OnSelectedIndexChanged="Change" AutoPostBack="True" runat="server"/> 

和

<asp:DropDownList ID="Combo" SelectedIndexChanged="Change" AutoPostBack="True" runat="server"/> 

之間的區別？

而且AutoPostBack =「True」屬性始終需要嗎？

Iam問，因爲它似乎我的OnSelectedIndexChanged事件似乎總是被調用兩次（編輯：當我使用SelectedIndexChanged，處理程序不會被調用）。

這是爲什麼？

編輯： 這些在我從兩次被觸發的事件中獲得的堆棧軌跡。後者似乎是從某種計時器中調用的。我從來沒有創造過一個時間，它必須是一些系統。

MyApp!MyNamespace.ListenControl.AuswahlGeändert(object sender = {System.Web.UI.WebControls.DropDownList}, System.EventArgs e = {System.EventArgs}) Zeile 44 C# 
    System.Web.dll!System.Web.UI.WebControls.ListControl.OnSelectedIndexChanged(System.EventArgs e = {System.EventArgs}) + 0x70 Bytes 
    System.Web.dll!System.Web.UI.WebControls.DropDownList.RaisePostDataChangedEvent() + 0x87 Bytes 
    System.Web.dll!System.Web.UI.WebControls.DropDownList.System.Web.UI.IPostBackDataHandler.RaisePostDataChangedEvent() + 0xb Bytes  
    System.Web.dll!System.Web.UI.Page.RaiseChangedEvents() + 0xa6 Bytes 
    System.Web.dll!System.Web.UI.Page.ProcessRequestMain(bool includeStagesBeforeAsyncPoint = true, bool includeStagesAfterAsyncPoint = true) + 0x5ce Bytes 
    System.Web.dll!System.Web.UI.Page.ProcessRequest(bool includeStagesBeforeAsyncPoint, bool includeStagesAfterAsyncPoint = true) + 0x84 Bytes 
    System.Web.dll!System.Web.UI.Page.ProcessRequest() + 0x51 Bytes 
    System.Web.dll!System.Web.UI.Page.ProcessRequestWithNoAssert(System.Web.HttpContext context) + 0x16 Bytes 
    System.Web.dll!System.Web.UI.Page.ProcessRequest(System.Web.HttpContext context) + 0x32 Bytes 
    App_Web_bm-nkhnz.dll!ASP.kfzpage_aspx.ProcessRequest(System.Web.HttpContext context = {System.Web.HttpContext}) + 0x26 Bytes C# 
    System.Web.dll!System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() + 0xb6 Bytes 
    System.Web.dll!System.Web.HttpApplication.ExecuteStep(System.Web.HttpApplication.IExecutionStep step = {System.Web.HttpApplication.CallHandlerExecutionStep}, ref bool completedSynchronously = true) + 0x4c Bytes 
    System.Web.dll!System.Web.HttpApplication.ApplicationStepManager.ResumeSteps(System.Exception error) + 0x133 Bytes 

    System.Web.dll!System.Web.HttpApplication.System.Web.IHttpAsyncHandler.BeginProcessRequest(System.Web.HttpContext context, System.AsyncCallback cb, object extraData) + 0x7c Bytes 
    System.Web.dll!System.Web.HttpRuntime.ProcessRequestInternal(System.Web.HttpWorkerRequest wr = {Microsoft.VisualStudio.WebHost.Request}) + 0x17c Bytes 
    System.Web.dll!System.Web.HttpRuntime.ProcessRequestNoDemand(System.Web.HttpWorkerRequest wr) + 0x63 Bytes 
    System.Web.dll!System.Web.HttpRuntime.ProcessRequest(System.Web.HttpWorkerRequest wr) + 0x47 Bytes 
    WebDev.WebHost.dll!Microsoft.VisualStudio.WebHost.Request.Process() + 0x165 Bytes 
    WebDev.WebHost.dll!Microsoft.VisualStudio.WebHost.Host.ProcessRequest(Microsoft.VisualStudio.WebHost.Connection conn = {System.Runtime.Remoting.Proxies.__TransparentProxy}) + 0x6c Bytes 
    [Anwendungsdomänenübergang] 
    WebDev.WebHost.dll!Microsoft.VisualStudio.WebHost.Server.OnSocketAccept(object acceptedSocket) + 0x7d Bytes 
    mscorlib.dll!System.Threading._ThreadPoolWaitCallback.WaitCallback_Context(object state) + 0x2f Bytes 
    mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x6f Bytes  
    mscorlib.dll!System.Threading._ThreadPoolWaitCallback.PerformWaitCallbackInternal(System.Threading._ThreadPoolWaitCallback tpWaitCallBack) + 0x53 Bytes 
    mscorlib.dll!System.Threading._ThreadPoolWaitCallback.PerformWaitCallback(object state) + 0x59 Bytes  

這是當事件被稱爲第二時間：

MyApp!MyNamespace.ListenControl.AuswahlGeändert(object sender = {System.Web.UI.WebControls.DropDownList}, System.EventArgs e = {System.EventArgs}) Zeile 44 C# 
     System.Web.dll!System.Web.UI.WebControls.ListControl.OnSelectedIndexChanged(System.EventArgs e = {System.EventArgs}) + 0x70 Bytes 
     System.Web.dll!System.Web.UI.WebControls.DropDownList.RaisePostDataChangedEvent() + 0x87 Bytes 
     System.Web.dll!System.Web.UI.WebControls.DropDownList.System.Web.UI.IPostBackDataHandler.RaisePostDataChangedEvent() + 0xb Bytes  
     System.Web.dll!System.Web.UI.Page.RaiseChangedEvents() + 0xa6 Bytes 
     System.Web.dll!System.Web.UI.Page.ProcessRequestMain(bool includeStagesBeforeAsyncPoint = true, bool includeStagesAfterAsyncPoint = true) + 0x5ce Bytes 
     System.Web.dll!System.Web.UI.Page.ProcessRequest(bool includeStagesBeforeAsyncPoint, bool includeStagesAfterAsyncPoint = true) + 0x84 Bytes 
     System.Web.dll!System.Web.UI.Page.ProcessRequest() + 0x51 Bytes 
     System.Web.dll!System.Web.UI.Page.ProcessRequestWithNoAssert(System.Web.HttpContext context) + 0x16 Bytes 
     System.Web.dll!System.Web.UI.Page.ProcessRequest(System.Web.HttpContext context) + 0x32 Bytes 
     App_Web_bm-nkhnz.dll!ASP.kfzpage_aspx.ProcessRequest(System.Web.HttpContext context = {System.Web.HttpContext}) + 0x26 Bytes C# 
     System.Web.dll!System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() + 0xb6 Bytes 
     System.Web.dll!System.Web.HttpApplication.ExecuteStep(System.Web.HttpApplication.IExecutionStep step = {System.Web.HttpApplication.CallHandlerExecutionStep}, ref bool completedSynchronously = true) + 0x4c Bytes 
     System.Web.dll!System.Web.HttpApplication.ApplicationStepManager.ResumeSteps(System.Exception error) + 0x133 Bytes 

     System.Web.dll!System.Web.HttpApplication.ResumeStepsFromThreadPoolThread(System.Exception error) + 0x25 Bytes 
     System.Web.dll!System.Web.HttpApplication.AsyncEventExecutionStep.ResumeStepsWithAssert(System.Exception error) + 0x28 Bytes  
     System.Web.dll!System.Web.HttpApplication.AsyncEventExecutionStep.OnAsyncEventCompletion(System.IAsyncResult ar) + 0x84 Bytes 
     System.Web.dll!System.Web.HttpAsyncResult.Complete(bool synchronous, object result, System.Exception error, System.Web.RequestNotificationStatus status) + 0x3e Bytes 
     System.Web.dll!System.Web.SessionState.SessionStateModule.PollLockedSessionCallback(object state) + 0x169 Bytes 
     mscorlib.dll!System.Threading._TimerCallback.TimerCallback_Context(object state) + 0x2f Bytes 
     mscorlib.dll!System.Threading.ExecutionContext.runTryCode(object userData) + 0x51 Bytes 
     [Übergang von Systemeigen zu Verwaltet] 
     [Übergang von Verwaltet zu Systemeigen] 
     mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x67 Bytes  
     mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x45 Bytes  
     mscorlib.dll!System.Threading._TimerCallback.PerformTimerCallback(object state) + 0x6b Bytes  
     [Anwendungsdomänenübergang] 

Answer 1

之間有什麼區別[ASP：DropDownList的1]和[ASP：DropDownList的2]？

SelectedIndexChanged不是asp:DropDownList標記的有效屬性，所以ASP.NET不會對它做任何事情。

我問，因爲它似乎我 OnSelectedIndexChanged事件似乎總是 被稱爲兩次......爲什麼 會這樣？

您的堆棧跟蹤表明第二個事件調用是由重入線程引起的。您是從網頁運行任何異步委託，使用客戶端回調還是使用第三方控件？

Answer 2

AutoPostBack屬性意味着控制的選擇將導致的柱。如果它沒有設置爲true，那麼你將需要做其他事情來提交表單（即點擊按鈕）

OnSelectedIndexChanged事件的可能性是檢查以確保您沒有添加事件處理器兩次。如果你已經在ASPX中定義了它，那麼不要將它添加到代碼隱藏中，反之亦然。

Answer 3

如果我正確地記得名爲OnSomething的事件更多用於內部使用（就像創建子類一樣，您將覆蓋OnSelectedIndexChanged）。所以我認爲使用SelectedIndexChange是個好習慣。

至於AutoPostBack，這是爲了確保頁面在項目發生更改時回發給服務器。如果未設置爲true，那麼您（服務器）將永遠不會在用戶單擊某個提交按鈕或執行其他導致和autopostback（在另一個控件上）之前更改。

編輯：

還有一兩件事，如果我不記得一個錯誤的方法OnSomething通常是調用事件東西（EDIT2的一個，這似乎不是在ASP中標記語言的情況下.NET（html）。在html中的OnSomething =「」映射到Something事件似乎，我的壞）。所以如果你寫一個名字可以改變的類「人」，你會這樣做：

public class Person 
{ 
    private string name; 
    public string Name 
    { 
     get { return name; } 
     set { name = value; OnNameChanged(new EventArgs()); } 
    } 

    protected OnNameChanged(EventArgs args) 
    { 
     if(NameChanged != null) 
      NameChanged(this, args); 
    } 

    public event EventHandler NameChanged; 
} 

或類似的東西。

微軟的例子可能比我的更好，雖然:-P：http://msdn.microsoft.com/en-us/library/5z57dxz2.aspx