类型“DropDownList”的控件“DropDownList1”必须放在具有 runat=server 的窗体标记内 的错误

Question

你的,控件必须放在有form中
<form id=.. runat=server>your DropDownList</form>

Answer 1

<form id=.. runat=server>
<table>
<tr>
<td><DropDownList id=... runat=server></td>
</tr>
</table>
</form>
搞定

Answer 2

<asp:DropDownList id="DropDownList1" runat="server"
     DataSource="<% databindingexpression %>"
     DataTextField="DataSourceField"
     DataValueField="DataSourceField"
     AutoPostBack="True|False"
     OnSelectedIndexChanged="OnSelectedIndexChangedMethod">   <asp:ListItem value="value" selected="True|False">
      Text
   </asp:ListItem></asp:DropDownList>

Answer 3

you:
 <form runat=server id=form1>
</form>
<asp:DropDownList id="DropDownList1" runat="server"
     DataSource="<% databindingexpression %>"
     DataTextField="DataSourceField"
     DataValueField="DataSourceField"
     AutoPostBack="True|False"
     OnSelectedIndexChanged="OnSelectedIndexChangedMethod">    //out of form
must:
<form runat=server id=form1><asp:DropDownList id="DropDownList1" runat="server"
     DataSource="<% databindingexpression %>"
     DataTextField="DataSourceField"
     DataValueField="DataSourceField"
     AutoPostBack="True|False"
     OnSelectedIndexChanged="OnSelectedIndexChangedMethod">    //in form
</form>//is ok