How do I keep my items in asp:dropdownlist after !Page.IsPostBack?-CodePudding

I am loading a list of value/text into a asp:dropdownlist by calling a stored procedure. I populate the dropdownlist on the PageLoad method inside a !Page.IsPostBack block like so:

if (!Page.IsPostBack)
{
     GetDropDownLists();
     DataBind();
}

And this is my code implementation for the backend:

protected void GetDropDownLists()
{
     DataTable dt = new DataTable();

     SqlConnection conn = new SqlConnection(connString);
     SqlCommand cmd = new SqlCommand("get_articletype", conn);
     cmd.CommandType = CommandType.StoredProcedure;
     SqlDataAdapter adapter = new SqlDataAdapter(cmd);
               
     adapter.Fill(dt);
     xArticleTypeList.Items.Clear();
     xArticleTypeList.Items.Insert(0, new ListItem("- Select.. -", "0"));
     xArticleTypeList.SelectedIndex = 0;
     xArticleTypeList.DataSource = dt;
     xArticleTypeList.DataValueField = "TypeValue";
     xArticleTypeList.DataTextField = "TypeName";
     xArticleTypeList.DataBind();
}

If my code isn't inside a !Page.IsPostBack block, after I click my save button the default value will always be the first item of the dropdownlist. But once I put my code inside the !Page.IsPostBack block my dropdownlist is empty. For reference here is the frontend implementation of my asp:dropdownlist.

<asp:DropDownList ID="xArticleTypeList" EnableViewState="true" AutoPostBack="true" CssClass="form-control" runat="server" />

I understand that there are other topics that cover this question, but none of the proposed solutions worked for me. Thanks you in advance for your inputs.

CodePudding user response：

Your problem is that you inserting the blank please select row BEFORE you bind. As a result, when you bind, you are blowing out the drop down.

Try it this way:

   protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
            LoadData();
    }


    void LoadData()
    {
        using (SqlConnection conn = new SqlConnection(Properties.Settings.Default.TEST4))
        {
            using (SqlCommand cmd = new SqlCommand("get_articletype", conn))
            {
                DataTable dt = new DataTable();
                cmd.CommandType = CommandType.StoredProcedure;
                conn.Open();
                dt.Load(cmd.ExecuteReader());

                xArticleTypeList.DataSource = dt;
                xArticleTypeList.DataValueField = "TypeValue";
                xArticleTypeList.DataTextField = "TypeName";
                xArticleTypeList.DataBind();

                xArticleTypeList.Items.Insert(0, new ListItem("- Select.. -", "0"));
            }
        }
    }

And GET RID of your extra call re-bind You have this:

 GetDropDownLists();
 DataBind();   <--- remove unless you need, or execute BEFORE the GetDropDownList()

So move your add/insert blank row to the drop down to AFTER the drop down data bind.

And REMOVE your DataBind() - you don't need it, and if for some reason you do, then move the DataBind() to before your load of the GetDropDownLists() - but my guess is that you just tossed that in the hope of making this work, and it going to cause the combo box to re-select - so remove unless you give a REALL GOOD HIGH quality outline and narrative as to why you have the DataBin() command there - (but as as noted, if you really, but really really do need to execute that DataBind() command - move it to before the load of the combo).

So, add the blank row after