在内容页面内查找控件

Question

我在母版页中使用以下代码来查找内容页面内的控件。在第一页加载时，它工作正常；但是，当我从内容页面上的下拉列表中选择一个项目并且启用了自动回发时，我收到错误“对象引用未设置到对象的实例”。这意味着 FindControl() 函数无法找到内容页面内的控件。出现这个问题的原因是什么？

PlaceHolder pHolder = (PlaceHolder)ContentPlaceHolder2.FindControl("PlaceHolder1");
Label lblPage = (Label)pHolder.FindControl("lblPageName");
if (lblPage.Text == "DesignSerachSQGrid")
{
}

编辑...

下拉列表的 HTML 代码：

 <telerik:RadComboBox ID="ddlSearchL1" runat="server" Width="400px" Skin="Office2007" 
                    onselectedindexchanged="ddlSearchL1_SelectedIndexChanged" 
                    AutoPostBack="True" Font-Names="Eras Medium ITC" Font-Size="X-Small" 
                    onprerender="ddlSearchL1_PreRender">
                   <Items>
                       <telerik:RadComboBoxItem runat="server" Text="Please Select ................" 
                           Value="Please Select ................" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Design Documents" 
                           Value="Design Documents" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Vendor Documents" 
                           Value="Vendor Documents" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Business Documents" 
                           Value="Business Documents" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Management Documents" 
                           Value="Management Documents" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Squad Check - Management" 
                           Value="Squad Check - Management" Font-Name="Eras Medium ITC" />
                       <telerik:RadComboBoxItem runat="server" Text="Transmittal - Management" 
                           Value="Transmittal - Management" Font-Name="Eras Medium ITC" />
                           <telerik:RadComboBoxItem runat="server" Text="Transmittal - Design" 
                           Value="Transmittal - Design" Font-Name="Eras Medium ITC" />
                           <telerik:RadComboBoxItem runat="server" Text="Squad Check - Design" 
                           Value="Squad Check - Design" Font-Name="Eras Medium ITC" />
            <telerik:RadComboBoxItem runat="server" Text="Transmittal - Vendor" 
                           Value="Transmittal - Vendor" Font-Name="Eras Medium ITC" />
                           <telerik:RadComboBoxItem runat="server" Text="Squad Check - Vendor" 
                           Value="Squad Check - Vendor" Font-Name="Eras Medium ITC" />
                   </Items>
           </telerik:RadComboBox>

Answer 1

您可以查看这篇文章： ASP .NET 2.0 MasterPages 和 FindControl()

/// <summary>
/// Finds a Control recursively. Note finds the first match and exists
/// </summary>
/// <param name="ContainerCtl"></param>
/// <param name="IdToFind"></param>
/// <returns></returns>
public static Control FindControlRecursive(Control Root, string Id)
{
    if (Root.ID == Id)
        return Root; 

    foreach (Control Ctl in Root.Controls)
    {
        Control FoundCtl = FindControlRecursive(Ctl, Id);
        if (FoundCtl != null)
            return FoundCtl;
    }

    return null;
}

使用它

this.dgItemList = FindControlRecursive(this.Master, "dgItemList") as DataGrid;