如何在使用sql数据源时在下拉列表中添加自定义项目

Question

我想知道当下拉列表绑定到sqldatasource时，是否有可能在下拉列表中添加一个项目作为预选项目。

Answer 1

Let's say you have the following .aspx markup:

<asp:DropDownList 
    ID="DropDownList1" 
    runat="server" 
    DataSourceID="SqlDS" 
    DataTextField="city" 
    DataValueField="id"></asp:DropDownList>
<asp:SqlDataSource 
    ID="SqlDS" 
    runat="server" 
    ConnectionString="<%$ ConnectionStrings:connectionString %>" 
    SelectCommand="SELECT [id],[city] FROM [cities]"></asp:SqlDataSource>

You can set the default drop down option to the second item in the drop down from server side like this:

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        DropDownList1.SelectedIndex = 1;
    }
}

Or from the client (using jQuery) like this:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.3/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
    $('#DropDownList1').get(0).selectedIndex = 1;
});

UPDATE:

If we use the drop down in my example - I retrieve a list of cities from the database to be displayed in the drop down.Let's say I want to add a new city that is not in the database, you can use UNION keyword for that and join your SQL data with a hardcoded value:

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        SqlDS.SelectCommand = "SELECT [id],[city] FROM [cities] UNION SELECT 10,'New York'";
    }
}

Answer 2

根据需要通过代码设置下拉列表的选定索引。