将“请选择”添加到从数据库中检索值的下拉列表中 [英] Add “Please Select” to Drop-down list that retrieves values from Data base

问题描述

我有一个下拉列表并使用SQL数据源来检索SQL服务器中的产品名称。现在，我想在下拉列表中添加请选择产品选项。

据我所知，我通过使用

I have a drop-down list and uses the SQL data source for it where I am retrieving the product names from SQL server. Now, I want to add "Please Select a product" Option to the drop-down list.
As far as my knowledge, I add options to drop-down list by using

<asp:ListItem Selected ="true" Value = "1">1</asp:ListItem>

因为，我没有添加值但是从DB中检索值，如何另外实现此选项并将其作为第一个位置添加到我的下拉列表中？



我尝试了下面的代码，但没有每当我选择其他值时，每次我都得到额外的请选择选项。

Since, I am not adding the values but retrieving the values from DB, how to achieve this Option additionally and add to it as first position to my drop-down list?

I tried the below code, but not able to do get at first position.Also, each time I am getting extra "please select" option whenever I am selecting other values.

protected void NameDropDownList_SelectedIndexChanged(object sender, EventArgs e)
        {
     NameDropDownList.Items.Insert(0, new ListItem("Please Select a product", "Please Select a product");
     SqlCommand cmd = new SqlCommand("SELECT ProductID, Price, Description, Rating FROM Product_Info Where Name = '" + NameDropDownList.Text + "'", conn);
     SqlDataReader myReader;
     conn.Open();
     myReader = cmd.ExecuteReader();
     while (myReader.Read()) {
     //Logic
    }
      conn.Close();
      myReader.Close();

这是我绑定数据的代码：

Here is my code behind where I bind the data:

<tr>
        <td class="style2">Name</td>
         <td>
               <asp:DropDownList ID="NameDropDownList" runat="server" Height="16px"
                   Width="130px" AutoPostBack="True" DataSourceID="NameSqlDataSource"
                   DataTextField="Name" DataValueField="Name"
                   onselectedindexchanged="NameDropDownList_SelectedIndexChanged">
               </asp:DropDownList>

               <asp:SqlDataSource ID="NameSqlDataSource" runat="server"
                   ConnectionString="<%$ ConnectionStrings:ProductsConnectionString %>"
                   SelectCommand="SELECT [Name] FROM [Product_Info]"></asp:SqlDataSource>
           </td>
   </tr>

我也将自动发布回真。提前谢谢

I also enables the Auto post back to true.Thanks in advance

推荐答案

ConnectionStrings：ProductsConnectionString％>
SelectCommand = SELECT [Name] FROM [Product_Info] > < / asp：SqlDataSource >
< / td >
< / tr >

ConnectionStrings:ProductsConnectionString %>" SelectCommand="SELECT [Name] FROM [Product_Info]"></asp:SqlDataSource> </td> </tr>

我也将自动发布回真。提前谢谢

I also enables the Auto post back to true.Thanks in advance

尝试

NameDropDownList.Items.Add("Please Select a product");

如果您首先清除列表，那么请选择产品将是列表中的第一项，然后填充列表的其余部分。



就个人而言，我不会在列表中提供帮助信息，而是将其放在工具提示或单独的标签上。



这假设你没有绑定列表..



如果数据绑定使用

If you clear the list first then the "Please Select a Product" will be the first item in the list and then populate the rest of the list.

Personally I would not put help information in the list but put it in on a tooltip or separate label.

This assumes you do not have a bound list..

If data bound use

NameDropDownList.Items.Insert(0, new ListItem("Please Select a product", "Please Select a product");

DropDownList1.Items.Insert（0，请选择选项）;

DropDownList1.Items.Insert(0,"Please Select Options");

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