C# 无法捕获中继器内文本框中的下拉选择值

我在中继器中有一个

DropDownList

，每当所选文本被更改时，我都必须在

TextBox

中显示它，但我得到的

对象引用未设置为对象的实例

错误

protected void Ddl_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList ddl   = (DropDownList)  sender;
    RepeaterItem item  = (RepeaterItem)  ddl .NamingContainer;
    TextBox txt        = (TextBox) item.FindControl("TextBox4");
    txt.Text           = ddl.SelectedItem.Text;
}

---

只需将Ddl dropdowns autopost back属性启用为true，并添加以下代码行：

protected virtual void RepeaterItemCreated(object sender, RepeaterItemEventArgs e)
{
    DropDownList MyList = (DropDownList)e.Item.FindControl("ddl");
    MyList.SelectedIndexChanged += ddl_SelectedIndexChanged;
}

protected void Ddl_SelectedIndexChanged(object sender, EventArgs e)
 {
     RepeaterItem item  = (RepeaterItem)  Page.FindControl("repeatorid");
     TextBox txt        = (TextBox) item.FindControl("TextBox4");
     txt.Text           = ddl.SelectedItem.Text;     
 }

---

哪条线路出故障了？TextBox也在中继器内吗？最后一行txt.Text=ddl.SelectedItem.Text；是，文本框在repeater@Newbie你确定定义了

txt

了吗？你所说的txt是什么意思？好的，检查下面的链接我的文本框在页脚模板中。