[英]How to make required field validator on dropdownlist?
我有一个下拉列表,在其中我为(选择频道...)添加了额外的值。 如果选择此值,则我希望显示一条必需的消息,我尝试的是:
<td>
<asp:DropDownList ID="ServiceChannelDropDownList" AppendDataBoundItems="true"
runat="server" DataTextField="Description" DataValueField="ID">
<asp:ListItem Value="-1" Text="Choose channel..." />
</asp:DropDownList>
<asp:RequiredFieldValidator ID="DropDownListRequiredFieldValidator" runat="server"
ControlToValidate="ServiceChannelDropDownList"
InitialValue="-1"
ErrorMessage="*"
</asp:RequiredFieldValidator>
</td>
不幸的是,这只是让我选择了初始值(数据库中自然不存在该初始值)而没有说不允许这样做。 如何解决呢?
您需要在绑定Dropdownlist数据的(.cs)后面的代码中添加默认值,而不是在.aspx页中添加默认值
ServiceChannelDropDownList.DataBind();
ServiceChannelDropDownList.Items.Insert(0, new ListItem("Choose channel...","-1"));
<td>
<asp:DropDownList ID="ServiceChannelDropDownList" AppendDataBoundItems="true"
runat="server" DataTextField="Description" DataValueField="ID">
<asp:ListItem Value="0" Text="Choose channel..." />
</asp:DropDownList>
<asp:RequiredFieldValidator ID="DropDownListRequiredFieldValidator" runat="server"
ControlToValidate="ServiceChannelDropDownList"
InitialValue="0"
ErrorMessage="*"
</asp:RequiredFieldValidator>
</td>
我需要将ValidationGroup添加到RequiredFieldValidator,例如,
<asp:RequiredFieldValidator ID="DropDownListRequiredFieldValidator" runat="server"
ControlToValidate="ServiceChannelDropDownList"
InitialValue="0"
ErrorMessage="Channel is required."
ValidationGroup="WorkflowValidation"
CssClass="ValidationCss"
EnableTheming="false">*
</asp:RequiredFieldValidator>
谢谢大家的帮助!
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