asp .net dropdownlist selectedindex not working

16,102

Solution 1

Looks like you are binding the drop down in the Page_Load...

Remember that when the drop down is changed, it does a post back (AutoPostBack='True'), and since you are binding on Page_Load it will simply rebind ever time the index is changed... not what you want!

you should do something like this:

if (!IsPostBack)
{  
    BindDropDownList1();      
}

Solution 2

Make sure ViewState is enabled (for change events), and move the code in your OnLoad to OnInit. This will prevent ViewState being overwritten as it occurs after Init and before Load.

Optionally you should also wrap the initialisation code inside an IsPostback check to avoid having to load the data on every request.

Solution 3

you can use this code:

  foreach (ListItem item in DropDownList1.Items)
     {
            if (item.Text == defaultText) 
            {
                item.Selected = true;
                break;
            }
     }

Solution 4

You can try overriding the OnPreRender method of the page:

protected override OnPreRender(EventArgs e)
{
    DropDownList1.SelectedIndex = Convert.ToInt32(ViewState["PageIndex"]);

    base.OnPreRender(e);
}

Also, make sure that EnableViewState is set to True.

View more solutions

16,102

Author by

Varun Sharma

Updated on June 14, 2022

Comments

Varun Sharma almost 2 years

I have the following piece of code:

DataRow CreateRow(DataTable dt, string name, string country)
    {
        DataRow dr = dt.NewRow();
        dr["Name"] = name;
        dr["Country"] = country;
        return dr;
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        // creating the data table
        DataTable dt = new DataTable("Student Details");

        // adding two columns Name and Country
        dt.Columns.Add("Name", typeof(String));
        dt.Columns.Add("Country", typeof(String));

        // create 3 rows        
        dt.Rows.Add(CreateRow(dt, "Varun", "India"));
        dt.Rows.Add(CreateRow(dt, "Li", "China"));
        dt.Rows.Add(CreateRow(dt, "Yishan", "China"));

        // create a data view 
        DataView dv = new DataView(dt);

        DropDownList1.DataSource = dv;
        DropDownList1.DataTextField = "Name";
        DropDownList1.DataValueField = "Country";
        DropDownList1.DataBind();
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        int x = DropDownList1.SelectedIndex;
        int temp = 0;
        temp++;
    }

and the markup looks like this:

<body>
    <form id="form1" runat="server">
    <div>

        <asp:Label ID="Label1" runat="server"></asp:Label>
        <br />
        <br />
        <asp:DropDownList ID="DropDownList1" runat="server" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged"
            AutoPostBack="true">
        </asp:DropDownList>

    </div>
    </form>
</body>

The problem is that label is always showing Varun no matter what I select. I debugged the code and found out that "DropDownList1.SelectedIndex" is always returning 0 for some reason.

I am not sure why is this happening. The function "DropDownList1_SelectedIndexChanged" is getting called every time I select something from the drop down list.

Thanks