If we want to avoid postback and instead of calling Dropdownlist' SelectedIndexChaned event,we can call Javascript OnChange event directly from from Aspx page.
We can understand this by an example:-
function show_message()
{
var ddl_gender = document.getElementById('<%=ddl_gender%>');
if(ddl_gender!=null)
{
if(ddl_gender.options[ddl_gender.selectedIndex].value.toUpperCase()=="SELECT")
{
alert('Please select any option");
return false;
}
if(ddl_gender.options[ddl_gender.selectedIndex].value.toUpperCase()=="MALE")
{
alert('Seleced option is Male");
return false;
}
if(ddl_gender.options[ddl_gender.selectedIndex].value.toUpperCase()=="FEMALE")
{
alert('Seleced option is Female");
return false;
}
}
}
<asp:DropDownList id="ddl_gender" runat="server"
onchange="show_message();" >
<asp:ListItem Text="--Select--" Value="Select">--Select--</asp:ListItem>
<asp:ListItem Text="Male" Value="Male">Male</asp:ListItem>
<asp:ListItem Text="Female" Value="Female">Female</asp:ListItem>
</asp:DropDownList>
We can also call show_message() function from code-behind as
In Page_Load()
{
if(!IsPostBack)
{
ddl_gender.Attributes.Add("onchange","show_message();");
}
}