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copied!<p>Here's what you do. </p> <p>In the ASPX code:</p> <pre><code><asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged"> <asp:ListItem Text="1" Value="1" /> <asp:ListItem Text="2" Value="2" /> <asp:ListItem Text="3" Value="3" /> <asp:ListItem Text="4" Value="4" /> </asp:DropDownList> <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged"> <asp:ListItem Text="1" Value="1" /> <asp:ListItem Text="2" Value="2" /> <asp:ListItem Text="3" Value="3" /> <asp:ListItem Text="4" Value="4" /> </asp:DropDownList> <asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged"> <asp:ListItem Text="1" Value="1" /> <asp:ListItem Text="2" Value="2" /> <asp:ListItem Text="3" Value="3" /> <asp:ListItem Text="4" Value="4" /> </asp:DropDownList> </code></pre> <p>In the codebehind:</p> <pre><code>protected void ddl_SelectedIndexChanged(object sender, EventArgs e) { DropDownList ddl = (DropDownList)sender; string value = ddl.SelectedValue; SetValue(DropDownList1, value); SetValue(DropDownList2, value); SetValue(DropDownList3, value); } protected void SetValue(DropDownList ddl, string value) { ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByValue(value)); } </code></pre> <p>Just typing <code>ddl1.SelectedValue = ddl2.SelectedValue</code> won't work, because <code>DropDownList.SelectedValue</code> is read-only. </p> <p>Note that I didn't just set the <code>SelectedIndex</code> of all the DDLs to that of the sender. You <strong>can</strong> use that in your example scenario, but if one of your DDLs ever has its ListItems in a different order from the others, the code will break. In my opinion, this makes it dangerous practice, but YMMV. </p> <p>Also, if you decide to generalize the SetValue method (I often add it as an extension method to the <code>DropDownList</code> control across the entire project), you should handle cases where the target value isn't found in the DDL, presumably by throwing an exception. You can also make a SetText version using <code>FindByText</code>.</p>

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