datagrid奇症，高手进来指点

[sasagun]

有一个DATAGRID，里面有两列，发现DELETE那列能触发事件响应，但模板列里的UP事件没有响应，是为什么？
<asp:ButtonColumn HeaderText="Delete item" ButtonType="LinkButton" Text="Delete" CommandName="Delete" />
<asp:TemplateColumn HeaderText="上移">
<ItemTemplate>
<center>
<asp:ImageButton CommandName="Up" Runat="server" ImageUrl="/Adminuser/images/up.gif"></asp:ImageButton>
</center>
</ItemTemplate>
</asp:TemplateColumn>

datagrid 的事件是OnItemCommand="ItemsGrid_Command"
代码如下
public void ItemsGrid_Command(Object sender, DataGridCommandEventArgs e)
{

switch(e.CommandName)
{

case "Delete":
this.Label1.Text="del";
break;

// Add other cases here, if there are multiple ButtonColumns in
// the DataGrid control.
case "Up":
this.Label1.Text="up";
break;

default:
// Do nothing.
break;

}

}