Question

dropdownlist的OnSelectedIndexChanged怎么做

drpLev1.DataSource = SW.BS.Facade.FTrainInfo.GetParentNode();
drpLev1.DataTextField = "TrainTypeName";
drpLev1.DataValueField = "ID";
drpLev1.DataBind();

int pid = Convert.ToInt32(drpLev1.DataValueField);
drpLev2.DataSource = SW.BS.Facade.FTrainInfo.GetSonNode(pid);
drpLev2.DataTextField = "TrainTypeName";
drpLev2.DataValueField = "ID";
drpLev2.DataBind();

怎样再将这两个关联起来？？？

OnSelectedIndexChanged在后台怎么写？？？

Answer 1

明白你的意思了。

你在设计视图点击drpLev1这个控件，然后按F4键，在右侧的属性栏里点击事件（雷）按钮，然后找到OnSelectedIndexChanged 事件,，双击，这时后台就会生成一个它的事件，然后你把下面的代码贴进去
int pid = Convert.ToInt32(drpLev1.DataValueField);
drpLev2.DataSource = SW.BS.Facade.FTrainInfo.GetSonNode(pid);
drpLev2.DataTextField = "TrainTypeName";
drpLev2.DataValueField = "ID";
drpLev2.DataBind();

不过我感觉下面这句可能有问题，你应该改成int pid = Convert.ToInt32(drpLev1.SelecedValue)
int pid = Convert.ToInt32(drpLev1.DataValueField);

另外，drpLev1控件，你还要设置一个属性 AutoPostBack=true

Answer 2

你的代码：
drpLev1.DataSource = SW.BS.Facade.FTrainInfo.GetParentNode();
drpLev1.DataTextField = "TrainTypeName";
drpLev1.DataValueField = "ID";
drpLev1.DataBind();
protected void drpLev1_SelectedIndexChanged(object sender, EventArgs e)
{
drpLev2.Items.Clear();
int pid = Convert.ToInt32(drpLev1.SelectedValue);
//这里是SelectedValue属性 ，不是DataValueField 字段
drpLev2.DataSource = SW.BS.Facade.FTrainInfo.GetSonNode(pid);
drpLev2.DataTextField = "TrainTypeName";
drpLev2.DataValueField = "ID";
drpLev2.DataBind();
}

先看看我的例子：
前台：
<asp:DropDownList ID="DDL1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDL1_SelectedIndexChanged">
</asp:DropDownList>
<asp:DropDownList ID="DDL2" runat="server" AutoPostBack="True" ">
</asp:DropDownList>

后台代码：
private void DataBindDDL1() //绑定DDL1的数据
{
string strSql = "select sname, childID from T1";
DataSet ds = SqlDBOperate.TheOnly.GetDataSet(strSql, "T1");
DDL1.DataSource = ds.Tables["T1"];
DDL1.DataTextField = "sname";
DDL1.DataValueField = "childID";
DDL1.DataBind();
}

private void DataBindDDL2() //绑定DDL2的数据
{
string strSql = string.Format("select childID , sname from T2 WHERE ID IN ( SELECT childID from T1 WHERE childID = '{0}')", DDL1.SelectedValue);
DataSet ds = SqlDBOperate.TheOnly.GetDataSet(strSql, "T2");
DDL2.DataSource = ds.Tables["T2"];
DDL2.DataTextField = "sname";
DDL2.DataValueField = "childID";
DDL2.DataBind();
}

//在DDL1的SelectedIndexChanged（）事件里面写绑定DDL2的数据
protected void DDL1_SelectedIndexChanged(object sender, EventArgs e)
{
DDL2.Items.Clear();
DataBindDDL2();
}

Answer 3

直接把drplev2的绑定过程放到里面去