如何在回发后保持DropDownList1选中的值？

3 回答

• 0

  您可以使用SESSION值来实现此目的，使用此值您需要从下拉列表中查找项目

  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);
       }
  

  回复于 2024-05-03T11:08:37+08:00
• 2

  How to implement cascading DropDownList ASP.Net control?

  不要 Response.Redirect() 到 SelectedIndexChanged() 中的同一页面 .
  最好将 DropDownList2 放在 UpdatePanel 中以避免整页回发，这是 DropDownList1 被清除的原因 .

  回复于 2024-05-03T11:08:37+08:00
• -1

  这可能是因为您的下拉列表在回发时再次绑定 . 尝试以下代码 .

  protected void Page_Load(object sender, EventArgs e)
          {
            if (!Page.IsPostBack)
                      {
                                 //write your dropdownlist1 binding code here
                      }
  
          }
  

  回复于 2024-05-03T11:08:37+08:00