所有下拉列表均在一次selectedIndexchange時重置

Question

我有這個項目正在注冊表格上，有四個下拉列表。在數據庫的頁面加載事件中填充了兩個

        if (!IsPostBack)
        {

            if (!getState()) { return; }
            if (!GetFaculty()) { return; }

        }

其余兩個填充在兩個的selectIndexchange上（州和學院）

  protected void ddlFaculty_OnSelectedIndexChanged(object sender, EventArgs e)
  {
        if (Page.IsPostBack) 
        { 
            try
            {
                string sqltext = @"Select Name from Department where FacultyID=" + this.ddlFaculty.SelectedValue.ToString();
                List<Department> mlist = new List<Department>();
                mlist = ServiceProvider.Instance().GetDepartmentService().GetDepartment_GetDepartment(sqltext);
                if (mlist.IsNullOrEmpty()) { return; }
                this.ddlDepartment.DataSource = mlist;
                this.ddlDepartment.DataTextField = "Name";
                this.ddlDepartment.DataValueField = "DepartmentID";
                this.ddlDepartment.DataBind();
                this.ddlDepartment.Items.Insert(0, new ListItem("--Select Department--", "0"));

            }
            catch (Exception ex) { return; }
        }

    }

    protected void ddstate_OnSelectedIndexChanged(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        { 

            try
            {
                string sqltext = @"Select Name from University where StateID=" + this.ddlState.SelectedValue.ToString();
                List<University> mlist = new List<University>();
                mlist = ServiceProvider.Instance().GetUniversityService().GetUniversity_UniversityName(sqltext);
                this.dDUniversity.DataSource = mlist;
                this.dDUniversity.DataTextField = "Name";
                this.dDUniversity.DataValueField = "UniversityID";
                this.dDUniversity.DataBind();
                this.dDUniversity.Items.Insert(0, new ListItem("-- Select University--", "0"));
                this.dDUniversity.SelectedIndex = 0;

            }
            catch (Exception ex) { return; };
        }
    }

現在的問題是，一旦我從ddUniversity的ddstate的selectedIndexChanged中選擇一個值，它就可以正常工作，然后從ddDepartment的ddfaculty的selectedIndexChanged中選擇值將自動重置ddUniversity，並且單擊“注冊”按鈕同樣會使所有內容擱置ddUniversity和ddDepartment。 這是我的html代碼

Answer 1

試用UpdatePanels或使用普通的AJAX加載DropDown