ASP.NET 2.0中给DropDownList服务器控件添加项的新方法

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在ASP.NET 2.0中，可以在数据绑定时，通过设置DropDownList的AppendDataBoundItems属性为true,在数据绑定之前添加一个新的项目，并且这个新加的项目会保存在ViewState之中。下面就是一个实现的例子：

C#代码

<%@ Page Language="C#" %>

<%@ Import Namespace="System.Data" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

ICollection CreateDataSource()

{

DataTable dt = new DataTable();

DataRow dr;

dt.Columns.Add(new DataColumn("id", typeof(Int32)));

dt.Columns.Add(new DataColumn("text", typeof(string)));

for (int i = 0; i < 6; i++)

{

dr = dt.NewRow();

dr[0] = i;

dr[1] = "列表项目 " + i.ToString();

dt.Rows.Add(dr);

}

DataView dv = new DataView(dt);

return dv;

}

protected void Button1_Click(object sender, EventArgs e)

{

Response.Write("<li>DropDownList1 您选择的项目：" + DropDownList1.SelectedValue

+ " ; " + DropDownList1.SelectedItem.Text);

Response.Write("<li>DropDownList2 您选择的项目：" + DropDownList2.SelectedValue

+ " ; " + DropDownList2.SelectedItem.Text);

}

protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)

{

DropDownList1.AppendDataBoundItems = true;

DropDownList1.Items.Add(new ListItem("-- 请选择一个选择项 --", ""));

DropDownList2.DataSource = DropDownList1.DataSource = CreateDataSource();

DropDownList2.DataTextField = DropDownList1.DataTextField = "text";

DropDownList2.DataValueField = DropDownList1.DataValueField = "id";

DropDownList1.DataBind();

DropDownList2.DataBind();

}

</script>

<title>DropDownList 补充例子</title>

</head>

<body>

<asp:DropDownList ID="DropDownList1" runat="server">

</asp:DropDownList>

<asp:DropDownList ID="DropDownList2" runat="server" AppendDataBoundItems="true">

<asp:ListItem Text="请选择" Value=""></asp:ListItem>

</asp:DropDownList>

<asp:Button ID="Button1" runat="server" Text="得到选择的值" OnClick="Button1_Click" />

</form>

</body>

</html>

VB.NET代码

<%@ Page Language="VB" AutoEventWireup="true" %>

<%@ Import Namespace="System.Data" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)

Response.Write("<li>DropDownList1 您选择的项目：" + DropDownList1.SelectedValue + _

" ; " + DropDownList1.SelectedItem.Text)

Response.Write("<li>DropDownList2 您选择的项目：" + DropDownList2.SelectedValue + _

" ; " + DropDownList2.SelectedItem.Text)

End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)

If Not IsPostBack Then

DropDownList1.AppendDataBoundItems = True

DropDownList1.Items.Add(New ListItem("-- 请选择一个选择项 --", ""))

DropDownList2.DataSource = CreateDataSource()

DropDownList1.DataSource = CreateDataSource()

DropDownList2.DataTextField = "text"

DropDownList1.DataTextField = "text"

DropDownList2.DataValueField = "id"

DropDownList1.DataValueField = "id"

DropDownList1.DataBind()

DropDownList2.DataBind()

End If

End Sub

Function CreateDataSource() As ICollection

Dim dt As DataTable = New DataTable()

Dim dr As DataRow

dt.Columns.Add(New DataColumn("id", GetType(System.Int32)))

dt.Columns.Add(New DataColumn("text", GetType(String)))

For i As Integer = 0 To 6

dr = dt.NewRow()

dr(0) = i

dr(1) = "列表项目 " + i.ToString()

dt.Rows.Add(dr)

Dim dv As DataView = New DataView(dt)

Return dv

End Function

</script>

<title>DropDownList 补充例子</title>

</head>

<body>

<asp:DropDownList ID="DropDownList1" runat="server">

</asp:DropDownList>

<asp:DropDownList ID="DropDownList2" runat="server" AppendDataBoundItems="true">

<asp:ListItem Text="请选择" Value=""></asp:ListItem>

</asp:DropDownList>

<asp:Button ID="Button1" runat="server" Text="得到选择的值" OnClick="Button1_Click" />

</form>

</body>

</html>

另外，还可以使用下面的方法添加：

protected void DropDownList1_DataBound(object sender, EventArgs e)
{
DropDownList1.Items.Insert(0,new ListItem("--请选择--", ""));
}