dropdownlist联动 用事件做

Brand--汽车品牌表
BID 主键，自动增长，汽车品牌编号
BName 汽车品牌

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Types--汽车型号表
TID 主键，自动增长，汽车型号编号
TName 汽车型号
BID 外键，与Brand表关联，

后台代码

public void DropDown1()
{
string sql = "select distinct(BName) from Brand";
DataTable data =(DataTable) BrandManager.lianDong(sql);
DropDownList1.DataTextField = "BName";
DropDownList1.DataValueField = "BName";
DropDownList1.DataSource = data;
DropDownList1.DataBind();
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
string sql = "select TName from Types T inner join Brand B on T.BID=B.BID where B.BName='" + DropDownList1.Text + "'";
DataTable data = (DataTable)BrandManager.lianDong(sql);
DropDownList2.DataTextField = "TName";
DropDownList2.DataValueField = "TName";
DropDownList2.DataSource = data;
DropDownList2.DataBind();
}

DropDownList1的值可以正常显示,就是DropDownList2不显示
我设断点调试过了,执行完DropDown1()这个方法后,不执行DropDownList1_SelectedIndexChanged!

SQL语句在SQL server 数据库中运行正常!

请高手帮帮忙!!!

是不是DropdownList的属性AutoPostBack=true，你看看自己改了没有

那就selectedindexchange事件(好像是这个,不然意思也差不多)里重新绑定另一个dropdownlist呗