关于c＃：如何在回发后保持DropDownList选中的值？

How to keep DropDownList1 selected value after postback?

我有两个下拉列表。一旦选择了DropDownList1值，DropDownList2将基于DropDownList1进行填充。

但刷新页面后，DropDownList 1所选值将更改为最上面的值(DropDownList由数据库填充)。

ASPX：

1	</asp:DropDownList>

政务司司长：

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protected void Page_Load(object sender, EventArgs e) {

DataTable subjects = new DataTable();

if (Page.IsPostBack == false) {
using (SqlConnection con = new SqlConnection(constring)) {

SqlDataAdapter adapter = new SqlDataAdapter("SELECT VehicleMake FROM VehicleDB", con);
adapter.Fill(subjects);

con.Open();

DropDownList1.DataSource = subjects;
DropDownList1.DataTextField ="VehicleMake";
DropDownList1.DataValueField ="";
DropDownList1.DataBind();

con.Close();
}
}
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e) {
string makename = DropDownList1.SelectedItem.Value;
keepname = makename;

Response.Redirect("default.aspx?QSVehicleMake="+makename);
}

相关讨论

为此，可以使用会话值，使用此值可以从下拉列表中查找项

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protected void Page_Load(object sender, EventArgs e)
{

jpyRATE = 1.4;

DataTable subjects = new DataTable();

if (Page.IsPostBack == false)
{
using (SqlConnection con = new SqlConnection(constring))
{

SqlDataAdapter adapter = new SqlDataAdapter("SELECT VehicleMake FROM VehicleDB", con);
adapter.Fill(subjects);

con.Open();

DropDownList1.DataSource = subjects;
DropDownList1.DataTextField ="VehicleMake";
DropDownList1.DataValueField ="VehicleMake";
DropDownList1.DataBind();

if(!String.IsNullOrEmpty(Session["vehiclemake"] as string))
{
DropDownList1.SelectedIndex =
DropDownList1.Items.IndexOf(DropDownList1.Items.FindByValue(Session["vehiclemake"].ToString()));
}

con.Close();

}

}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{

string makename = DropDownList1.SelectedItem.Value;
keepname = makename;
Session["vehiclemake"] = keepname;
Response.Redirect("default.aspx?QSVehicleMake="+makename);
}