解决asp.net中listbox的SelectedIndex的取值为-1

protected void Page_Load(object sender, System.EventArgs e)
{

...

string[] maindir = stypes.Split(new char[] { ',' });
for (int i = 0; i < maindir.Length; i++)
{
lbclasss.Items.Add(new ListItem(maindir[i]));
}

...

}

//lbclasss.SelectedIndex 每次取值都为-1

protected void btntypedel_Click(object sender, EventArgs e)
{
if (lbclasss.SelectedIndex > -1)
{
lbclasss.Items.RemoveAt(lbclasss.SelectedIndex);
}
}

解决方法：

protected void Page_Load(object sender, System.EventArgs e)
{

lbclasss.SelectedValue = Request["lbclasss"];

　　...

　　}