Cannot have multiple items selected in a DropDownList

Mainly this issue occurred when in dropdown value is already selected and next step we are again trying to select a dropdown value by FindByText or FindByValue using dropdown item's property.

<asp:DropDownList ID="DropDownList1" runat="server">

    <asp:ListItem Value="-1">Select</asp:ListItem>

    <asp:ListItem Value="0">1</asp:ListItem>

    <asp:ListItem Value="1">2</asp:ListItem>

    <asp:ListItem Value="2">3</asp:ListItem>

</asp:DropDownList>

Below code raise an error “Cannot have multiple items selected in a DropDownList”

protected void Page_Load(object sender, EventArgs e)

{

    if (!Page.IsPostBack)

    {

        try

        {

            DropDownList1.SelectedValue = "0";

            DropDownList1.Items.FindByValue("1").Selected = true;

            //OR

            //DropDownList1.Items.FindByText("2").Selected = true;

        }

        catch (Exception ex)

        {

            throw ex;

        }

    }

}

To overcome this issue clear dropdown selection before next selection of dropdown.

protected void Page_Load(object sender, EventArgs e)

{

    if (!Page.IsPostBack)

    {

        try

        {

            DropDownList1.SelectedValue = "0";

            DropDownList1.ClearSelection();

            DropDownList1.Items.FindByValue("1").Selected = true;

            //OR

            //DropDownList1.Items.FindByText("2").Selected = true;

        }

        catch (Exception ex)

        {

            throw ex;

        }

    }

}