DropDownList如果放在datagride里面，怎么触发它的SelectedIndexChanged事件？
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OnItemDataBound事件里.Attributes.Add
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在datagrid的itemdatabind事件里面添加
DropDownList.SelectedIndexChanged+=new System.EventHandler(DropDownList_SelectedIndexChanged);
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自己写委托事件
DropDownList.SelectedIndexChanged+=new System.EventHandler(DropDownList_SelectedIndexChanged);
应该在ItemCreated里写