如何添加一个空的第一个条目做一个&LT; ASP:DropDownList的&GT ;? [英] How do I add an empty first entry do an <asp:DropDownList>?
问题描述
我有一个下拉列表中,我有一个数据源,我有的AutoPostBack
设置为真正
我想补充的第一入口,以说像数据源---选择国家---,然后选择该条目不会导致回发。
这感觉就像它应该是很容易做到的,但我不能似乎能够找到一个很好的解决方案。
谢谢你。
I have a dropdown, I have a datasource, I have AutoPostBack
set to true
.
I want to add a first entry to the datasource that says something like "--- select country ---" and selecting this entry won't cause postback.
This feels like it should be easy to do, yet I can't seem to be able to find a good solution.
Thanks.
推荐答案
在你的aspx页面(的重要组成部分,是处理数据绑定事件和设置的CausesValidation =true以强制一个下拉列表的验证):
In your aspx page (the important part is handling the DataBound event and setting CausesValidation="true" to force validation of a drop down list):
<asp:DropDownList ID="ddlCountries" runat="server" DataSourceID="dsCountries" AutoPostBack="true" OnDataBound="ddlCountries_DataBound" CausesValidation="true" />
<asp:RequiredFieldValidator ID="rfvCountries" runat="server" ControlToValidate="ddlCountries" Display="Dynamic" ErrorMessage="Please select a country." />
在您的codebehind(重要的是,插入项的值的String.Empty为必填字段校验工作!)
In your codebehind (it is important that the value of the inserted item is String.Empty for the required field validator to work!):
protected void ddlCountries_DataBound(Object sender, EventArgs e)
{
ddlCountries.Items.Insert(0, new ListItem("--- select country ---", String.Empty));
}
注意:如果您不希望验证的消息显示,设置显示属性设置为无
Note: If you don't want the validator's message to display, set the "Display" property to "None".
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