在嵌套中繼器的頁腳內查找控件？ （.NET 2.0，C＃）

Question

當在嵌套中繼器的頁腳中查找數量框控件時，收到空引用錯誤。當執行OnItemCommand函數時（不是數據綁定到中繼器時發生此錯誤，這是我之前遇到但已修復的問題）。

我是一個新手，所以我不明白所有這一切，我試圖通過它，因爲我去，但我不知道爲什麼FindControl裏面的一個foreach repeateritem（其中msdn says includes the header and footer of a repeater！ ）在該中繼器的頁腳中找不到控制。這讓我瘋狂。

請幫忙！

更新：我更改了代碼，但仍然存在相同的問題 - 我錯誤地引用了ddl，並且我一直將對象引用設置爲未設置爲對象的實例。

下面的代碼：

.NET：

<asp:Content ID="ProductRepeater" ContentPlaceHolderID="ProductRepeater" Runat="Server"> 
    <asp:Repeater ID="chairRepeater" OnItemCommand="productRepeater_ItemCommand" OnItemDataBound="chairRepeater_ItemDataBound" runat="server"> 
    <ItemTemplate> 
     ... 
     <asp:Repeater ID="variantRepeater" OnItemDataBound="variantRepeater_ItemDataBound" runat="server"> 
     <ItemTemplate> 
      <li> 
      <asp:RadioButton ID="radioBtn" GroupName="collections" runat="server"></asp:RadioButton> 
      <asp:HiddenField ID="variantId" runat="server" /> 
      <asp:Literal ID="Image1" runat="server" /> 
      &nbsp; 
      <asp:Literal ID="collectionName" runat="server" /> 
      &nbsp;&ndash;&nbsp; 
      <asp:Literal ID="listPrice" runat="server" /> 
      </li> 
     </ItemTemplate> 
     <FooterTemplate> 
     </ul> 
      <asp:DropDownList ID="quantityLister" runat="server" /> 
     </FooterTemplate> 
     </asp:Repeater> 
     <asp:ImageButton ID="addToCart" ImageUrl="assets/images/_addtocart.gif" runat="server" /> 
     </div> 
     </div> 
    </ItemTemplate> 
    <SeparatorTemplate> <br /> 
    </SeparatorTemplate> 
    <FooterTemplate> </FooterTemplate> 
    </asp:Repeater> 

C＃：

protected void productRepeater_ItemCommand(object source, RepeaterCommandEventArgs e) 
{ 
    BasketHelper basketHelper = new BasketHelper(SiteContext.Current.ShoppingBasketName); 
    OrderForm orderForm = basketHelper.GetOrderForm(); 
    bool basketUpdated = false; 

    string catalogName = ConfigurationManager.AppSettings["PatioCatalogName"]; 
    string productId = ((HiddenField)e.Item.FindControl("productId")).Value; 
    string variantId = ""; 

    Repeater variantRepeater = (Repeater)e.Item.FindControl("variantRepeater"); 
    foreach (RepeaterItem item in variantRepeater.Items) 
    { 
     RadioButton radioBtn = item.FindControl("radioBtn") as RadioButton; 

     if (radioBtn.Checked == true) 
     { 
      variantId = ((HiddenField)item.FindControl("variantId")).Value; 
     } 
    } 
     int quantity = 0; 
     DropDownList quantityLister = (DropDownList)variantRepeater.FindControl("quantityLister"); 
     string ddlvalue = quantityLister.SelectedValue; 
     int.TryParse(ddlvalue, out quantity); 

     if (quantity > 0) 
     { 
      orderForm.LineItems.Add(new LineItem(catalogName, productId, variantId, quantity)); 
      basketUpdated = true; 
     } 
    if (basketUpdated) 
    { 
     basketHelper.Basket.Save(); 

     Response.Redirect(
      String.Format(
       CultureInfo.InvariantCulture, 
       "~/cart.aspx?{0}={1}", 
       SiteConstants.ActionQueryStringKey, 
       SiteConstants.RunPipelineCartAction), 
      true); 
    } 
} 

而這裏的時候我按下購買按鈕我得到的錯誤：

Server Error in '/' Application. 
Object reference not set to an instance of an object. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. 

Source Error: 

Line 116:   int quantity = 0; 
Line 117:   DropDownList quantityLister = (DropDownList)variantRepeater.FindControl("quantityLister"); 
Line 118:   string ddlvalue = quantityLister.SelectedValue; 
Line 119:   int.TryParse(ddlvalue, out quantity); 
Line 120: 


Source File: c:\Inetpub\patios\chaircovers.aspx.cs Line: 118 

Stack Trace: 

[NullReferenceException: Object reference not set to an instance of an object.] 
    ChairCovers.productRepeater_ItemCommand(Object source, RepeaterCommandEventArgs e) in c:\Inetpub\patios\chaircovers.aspx.cs:118 
    System.Web.UI.WebControls.Repeater.OnItemCommand(RepeaterCommandEventArgs e) +108 
    System.Web.UI.WebControls.Repeater.OnBubbleEvent(Object sender, EventArgs e) +68 
    System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37 
    System.Web.UI.WebControls.RepeaterItem.OnBubbleEvent(Object source, EventArgs e) +123 
    System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37 
    System.Web.UI.WebControls.ImageButton.OnCommand(CommandEventArgs e) +111 
    System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument) +176 
    System.Web.UI.WebControls.ImageButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10 
    System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13 
    System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36 
    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565 

Answer 1

所以我改變了這種：

DropDownList quantityLister = (DropDownList)variantRepeater.FindControl("quantityLister"); 

對此：

DropDownList quantityLister = variantRepeater.Controls[variantRepeater.Controls.Count - 1].FindControl("quantityLister") as DropDownList; 

它工作。

Answer 2

它已經因爲我這樣做了一段時間，但是作爲一個主意，嘗試，

，因爲它是嵌套，嵌套頭或HTML頁腳控制，實際名稱是外中繼器控制的串聯名稱，（我認爲），下劃線（'_'）和內部頁眉/頁腳控件的名稱......你是否在你的發現中使用了這個名稱？

第二個建議： 更改代碼年

foreach (RepeaterItem item in variantRepeater.Items) 
{ 
     decimal quantity = 0;   
     decimal.TryParse(((DropDownList)item.FindControl(
      "quantityLister")).SelectedValue, out quantity); 
     if (quantity > 0) 
     { 
      string variantId = ((HiddenField)item.FindControl("variantId")).Value; 
      orderForm.LineItems.Add(
       new LineItem(catalogName, productId, variantId, quantity)); 
      basketUpdated = true; 
     } 
} 

並將其更改爲：再次

foreach (RepeaterItem item in variantRepeater.Items) 
{ 
     decimal quantity = 0;   
     decimal.TryParse(((DropDownList)item.FindControl(
      "quantityLister")).SelectedValue, out quantity); 
     if (quantity > 0) 
     { 
      if (item == null) 
       throw new ApplicationException(
        "Can't locate RepeaterItem"); 
      object obj = item.FindControl("variantId"); 
      if (obj == null) 
      { 
       string sNL = Environment.NewLine; 
       StringBuilder sb = new StringBuilder(
        "Can't locate variantId HiddenField" + sNL + 
        "item Controls are:" + sNL); 
       foreach(Control ctrl in item.Controls) 
        sb.Append(ctrl.Name + sNL); 

       throw new ApplicationException(sb.ToString());     
      } 
      if (!(obj is HiddenField)) 
       throw new ApplicationException(
        "variantId is not a HiddenField"); 
      HiddenField hfld = obj as HiddenField; 

      string variantId = hfld.Value; 
      orderForm.LineItems.Add(new LineItem(
       catalogName, productId, variantId, quantity)); 
      basketUpdated = true; 
     } 
} 

運行，看看是什麼錯誤......