html5 validation on asp:dropdownlist

问题

Is there a way to use html5 validation (not asp:RequiredFieldValidator) on an asp:dropdownlist. I have already tried this:

<asp:DropDownList ID="ExpenseLineTypeDdl" required="required" initialvalue="0" CssClass="form-control" runat="server">  
     <asp:ListItem Value="0">Please Select a Type</asp:ListItem>    
</asp:DropDownList>

I'd Like it to work similar to this (except for an asp:dropdownlist):

<asp:TextBox runat="server" required="required"></asp:TextBox>

回答1:

I had to get rid of {initialvalue="0"} and set the initial listitem's {value=""}:

<asp:DropDownList ID="ExpenseLineTypeDdl" required="required" CssClass="form-control" runat="server">  
      <asp:ListItem Value="">Please Select a Type</asp:ListItem>    
</asp:DropDownList>

来源：https://stackoverflow.com/questions/31296146/html5-validation-on-aspdropdownlist