C# 内容页上的母版页控件

我在母版页上获得了以下代码：

<u1>
...............
............
.............
</u1>
<ul>
    <li id="link1" runat="server"><a href="mytestfile.aspx">Test Files</a></li>
    <li id="link2" runat="server"><a href="mylistitemtest.aspx">List Item Test</a></li>
    <li id="link3" runat="server"><a href="Mytest2.aspx">Some Test</a></li>    
</ul> 

但我得到的错误是：

---

“对象引用未设置为对象实例”

您的母版页上没有id为

nav_link1

的控件，它是

link1

在ContentPage上设置@MasterType指令

<%@ MasterType virtualpath="~/Masters/Master1.master" %>

<%@ MasterType virtualpath="~/Masters/Master1.master" %>

ContentPlaceHolder mpContentPlaceHolder;
TextBox mpTextBox;
mpContentPlaceHolder = 
  (ContentPlaceHolder)Master.FindControl("ContentPlaceHolder1");
if(mpContentPlaceHolder != null)
{
    mpTextBox = 
        (TextBox) mpContentPlaceHolder.FindControl("TextBox1");
    if(mpTextBox != null)
    {
        mpTextBox.Text = "TextBox found!";
    }
}