如何检查radiobuttonlist是否在javascript中检查

Question

我尝试使用以下代码检查单选按钮选择，但即使在选择后也显示警告

    <script type="text/javascript">
    function validate() 
    {
    if (!document.getElementById('<%= Radiobuttonlist1.ClientID %>').checked) 
         {
                    alert("Please select type");
                    return false;
         }
    }
    </script>

        <asp:radiobuttonlist ID="Radiobuttonlist1" runat="server" 
                    RepeatDirection="Horizontal" >
                <asp:ListItem>Text</asp:ListItem>
                <asp:ListItem>Number</asp:ListItem>
                <asp:ListItem>Character</asp:ListItem>
                </asp:radiobuttonlist>

        <asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="return validate();" onclick="Button1_Click"/>