FindControl找不到控件

Question

I have a problem with FindControl function. The problem is as follow:

aspx:

<asp:Content ID="MainContent" ContentPlaceHolderID="MainContent" runat="server">
  <ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
  </ajaxToolkit:ToolkitScriptManager>

  <table class="inputTable">
            <tr><td>
                <asp:CheckBox ID="Extern" AutoPostBack="True" OnCheckedChanged="OnCheckedChangedMethod" runat="server" />
                </td><td>Externes Unternehmen</td></tr>
    <tr>         
        <td>
            <asp:TextBox ID="Firmierung" runat="server"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
                ControlToValidate="Firmierung" Display="Dynamic" 
                ErrorMessage="RequiredFieldValidator"
                Text="Bitte geben Sie die Firmierung ein."></asp:RequiredFieldValidator>                
        </td>
    </tr>
  </table>  

aspx.cs:

protected void OnCheckedChangedMethod(object sender, EventArgs e)
    {            
        if (Extern.Checked)
        {                
            Control ctr = FindControl("RequiredFieldValidator1");                
            if (ctr != null)
            {
                ctr.Visible = false;
            }
        }
        else
        {                
        }
    }

But FindControl didn't work, it couldn't find that control. Was I wrong at any point? Thanks in advance.

Answer 1

ASP.NET creates a field for you, as it is located inside a Content : this.RequiredFieldValidator1 in your page.

The FindControl way would be like this (find it in the master page's content panel):

Control ctr = Master.FindControl("MainContent")
    .FindControl("RequiredFieldValidator1");

Answer 2

Based on your limited source, you should be able to simplify your code behind method to:

protected void OnCheckedChangedMethod(object sender, EventArgs e)
{            
    this.RequiredFieldValidator1.Visible = this.Extern.Checked;
}

There should be no need for the use of FindControl().

When you type "this.", if you don't see RequiredFieldValidator1 appear in your intellisense, and assuming you are using ASP.NET 2.0 or greater, check your VS.NET warnings to see if your .aspx has a warning message with an associated "Generation of designer file failed". If so, you must correct the warning.