how to prevent dropdownlists with same set of values select same value?

Question

I have 3 dropdowns and each one is populated with same set of values say a,b and c

eg: if i select 'a' from the dropdown and there is another dropdown with the same value 'a' selected. i should get an err msg.

How is this possible.

Answer 1

Use CompareValidator control like this:

<form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="ddl1" runat="server">
            <asp:ListItem Text="a" Value="a"></asp:ListItem>
            <asp:ListItem Text="b" Value="b"></asp:ListItem>
        </asp:DropDownList>
        <asp:DropDownList ID="ddl2" runat="server">
            <asp:ListItem Text="a" Value="a"></asp:ListItem>
            <asp:ListItem Text="b" Value="b"></asp:ListItem>
        </asp:DropDownList>
        <asp:DropDownList ID="ddl3" runat="server">
            <asp:ListItem Text="a" Value="a"></asp:ListItem>
            <asp:ListItem Text="b" Value="b"></asp:ListItem>
        </asp:DropDownList>
        <asp:CompareValidator ID="CompareValidator1" runat="server"
            ErrorMessage="DropDownList 1 can't be equal DropDownList 2"
            ControlToCompare="ddl1" ControlToValidate="ddl2" Operator="NotEqual"></asp:CompareValidator>
        <asp:CompareValidator ID="CompareValidator2" runat="server"
            ErrorMessage="DropDownList 2 can't be equal DropDownList 3"
            ControlToCompare="ddl2" ControlToValidate="ddl3" Operator="NotEqual"></asp:CompareValidator>
         <asp:CompareValidator ID="CompareValidator3" runat="server"
            ErrorMessage="DropDownList 1 can't be equal DropDownList 3"
            ControlToCompare="ddl2" ControlToValidate="ddl3" Operator="NotEqual"></asp:CompareValidator>
    </div>
</form>