DropDownList的SelectedIndexChanged事件搞糊涂了
现在想完成这样一个操作,用DropDownList的选择项来控制Label的显示.如果为第一项时隐藏,第二项时显示.设置了DropDownList1_SelectedIndexChanged事件,在把DropDownList的autopostback属性设置为true的时候,通过在DropDownList选择来改变SelectedIndex是可以触发SelectedIndexChanged事件的,但我如果通过一个Button来设置DropDownList的SelectedIndex为0的时候它不触发这个事件.不明白了.我这里用代码也改变了DropDownList的SelectedIndex,为什么就不触发SelectedIndexChanged事件呢?是不是事件执行顺序的问题?

测试代码如下:
    <form   id= "form1 "   runat= "server ">
                <asp:DropDownList   ID= "DropDownList1 "   runat= "server "   OnSelectedIndexChanged= "DropDownList1_SelectedIndexChanged "
                        Width= "171px ">
                        <asp:ListItem> 1 </asp:ListItem>
                        <asp:ListItem> 2 </asp:ListItem>
                        <asp:ListItem> 3 </asp:ListItem>
                </asp:DropDownList>
                <asp:Label   ID= "Label1 "   runat= "server "   Text= "adsgasgasg "   Visible= "False "   Width= "232px "> </asp:Label>
                <br   />
                <br   />
                <asp:Button   ID= "Button1 "   runat= "server "   OnClick= "Button1_Click "   Text= "Button "   />
       
        </form>

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后台


        protected   void   DropDownList1_SelectedIndexChanged(object   sender,   EventArgs   e)
        {
                if   (this.DropDownList1.SelectedValue   ==   "1 ")
                {
                        this.Label1.Visible   =   false;
                }
                else
                {
                        this.Label1.Visible   =   true;
                }
        }
        protected   void   Button1_Click(object   sender,   EventArgs   e)
        {
                this.DropDownList1.SelectedValue   =   "1 ";
        }

------解决方案--------------------
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
ChangeText();
}
protected void Button1_Click(object sender, EventA