Display alert message based on ASP.Net DropDownList selected Text using C# and VB.Net

Hi kankon,

Please refer sample below.

HTML

<asp:DropDownList ID="ddlCities" runat="server" AutoPostBack="true" OnSelectedIndexChanged="OnSelectedIndexChanged">
    <asp:ListItem Text="" Value="0"></asp:ListItem>
    <asp:ListItem Text="Mumbai" Value="1" Selected="True"></asp:ListItem>
    <asp:ListItem Text="Delhi" Value="2"></asp:ListItem>
</asp:DropDownList>
<script type="text/javascript">
    function OpenAlert(message) {
        alert(message);
    }
</script>

Code

C#

protected void OnSelectedIndexChanged(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(ddlCities.SelectedItem.Text))
    {
        ClientScript.RegisterStartupScript(this.GetType(), "message", "OpenAlert('Bad name.')", true);
    }
    else
    {
        ClientScript.RegisterStartupScript(this.GetType(), "message", "OpenAlert('Selected city " + ddlCities.SelectedItem.Text + ".')", true);
    }
}

VB.Net

Protected Sub OnSelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If String.IsNullOrEmpty(ddlCities.SelectedItem.Text) Then
        ClientScript.RegisterStartupScript(Me.GetType(), "message", "OpenAlert('Bad name.')", True)
    Else
        ClientScript.RegisterStartupScript(Me.GetType(), "message", "OpenAlert('Selected city " & ddlCities.SelectedItem.Text & ".')", True)
    End If
End Sub

Screenshot