技术资料 > .Net专区 > Asp.Net开发 : ASP.NET ViewState 初探 (2)

ASP.NET ViewState 初探 (2)

March 25,2004

请看下面的示例：要在 Web 页上显示一个项目列表，而每个用户需要不同的列表排序。项目列表是静态的，因此可以将这些页面绑定到相同的缓存数据集，而排序顺序只是用户特定的 UI 状态的一小部分。ViewState 非常适合于存储这种类型的值。代码如下：

[Visual Basic]
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
      <title>用于页面 UI 状态值的 ViewState/title>
</HEAD>
<body>
      <form runat="server">
         <H3>
            在 ViewState 中存储非控件状态
         </H3>
         <P>
            此示例将一列静态数据的当前排序顺序存储在 ViewState 中。<br>
            单击列标题中的链接，可按该字段排序数据。<br>
            再次单击该链接，将按相反顺序排序。
            <br><br><br>
            <asp:datagrid id="DataGrid1" runat="server"
OnSortCommand="SortGrid" BorderStyle="None" BorderWidth="1px"
BorderColor="#CCCCCC" BackColor="White" CellPadding="5" AllowSorting="True">
                  <HeaderStyle Font-Bold="True" ForeColor="White"
BackColor="#006699">
                  </HeaderStyle>
            </asp:datagrid>
         </P>
      </form>
</body>
</HTML>
<script runat="server">

' 在 ViewState 中跟踪 SortField 属性
Property SortField() As String

      Get
         Dim o As Object = ViewState("SortField")
         If o Is Nothing Then
            Return String.Empty
         End If
         Return CStr(o)
      End Get

      Set(Value As String)
         If Value = SortField Then
            ' 与当前排序文件相同，切换排序方向
            SortAscending = Not SortAscending
         End If
         ViewState("SortField") = Value
      End Set

End Property

' 在 ViewState 中跟踪 SortAscending 属性
Property SortAscending() As Boolean

      Get
         Dim o As Object = ViewState("SortAscending")
         If o Is Nothing Then
            Return True
         End If
         Return CBool(o)
      End Get

      Set(Value As Boolean)
         ViewState("SortAscending") = Value
      End Set

End Property

Private Sub Page_Load(sender As Object, e As EventArgs) Handles MyBase.Load

      If Not Page.IsPostBack Then
         BindGrid()
      End If

End Sub

Sub BindGrid()

      ' 获取数据
      Dim ds As New DataSet()
      ds.ReadXml(Server.MapPath("TestData.xml"))

      Dim dv As New DataView(ds.Tables(0))

      ' 应用排序过滤器和方向
      dv.Sort = SortField
      If Not SortAscending Then
         dv.Sort += " DESC"
      End If

      ' 绑定网格
      DataGrid1.DataSource = dv
      DataGrid1.DataBind()

End Sub

Private Sub SortGrid(sender As Object, e As DataGridSortCommandEventArgs)
      DataGrid1.CurrentPageIndex = 0
      SortField = e.SortExpression
      BindGrid()
End Sub

</script>

[C#]
<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
      <title>用于页面 UI 状态值的 ViewState</title>
</HEAD>
<body>
      <form runat="server">
         <H3>
            在 ViewState 中存储非控件状态
         </H3>
         <P>
            此示例将一列静态数据的当前排序顺序存储在 ViewState 中。<br>
            单击列标题中的链接，可按该字段排序数据。<br>
            再次单击该链接，将按相反顺序排序。
            <br><br><br>
            <asp:datagrid id="DataGrid1" runat="server" OnSortCommand="SortGrid"
            BorderStyle="None" BorderWidth="1px" BorderColor="#CCCCCC"
            BackColor="White" CellPadding="5" AllowSorting="True">
                  <HeaderStyle Font-Bold="True" ForeColor="White" BackColor="#006699">
                  </HeaderStyle>
            </asp:datagrid>
         </P>
      </form>
</body>
</HTML>
<script runat="server">

// 在 ViewState 中跟踪 SortField 属性
string SortField {

      get {
         object o = ViewState["SortField"];
         if (o == null) {
            return String.Empty;
         }
         return (string)o;
      }

      set {
         if (value == SortField) {
            // 与当前排序文件相同，切换排序方向
            SortAscending = !SortAscending;
         }
         ViewState["SortField"] = value;
      }
}

// 在 ViewState 中跟踪 SortAscending 属性
bool SortAscending {

      get {
         object o = ViewState["SortAscending"];
         if (o == null) {
            return true;
         }
         return (bool)o;
      }

      set {
         ViewState["SortAscending"] = value;
      }
}

void Page_Load(object sender, EventArgs e) {

      if (!Page.IsPostBack) {
         BindGrid();
      }
}

void BindGrid() {

      // 获取数据
      DataSet ds = new DataSet();
      ds.ReadXml(Server.MapPath("TestData.xml"));

      DataView dv = new DataView(ds.Tables[0]);

      // 应用排序过滤器和方向
      dv.Sort = SortField;
      if (!SortAscending) {
         dv.Sort += " DESC";
      }

      // 绑定网格
      DataGrid1.DataSource = dv;
      DataGrid1.DataBind();
}

void SortGrid(object sender, DataGridSortCommandEventArgs e) {

      DataGrid1.CurrentPageIndex = 0;
      SortField = e.SortExpression;
      BindGrid();
}

</script>

下面是上述两个代码段中引用的 testdata.xml 的代码：

<?xml version="1.0" standalone="yes"?>
<NewDataSet>
  <Table>
<pub_id>0736</pub_id>
<pub_name>New Moon Books</pub_name>
<city>Boston</city>
<state>MA</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>0877</pub_id>
<pub_name>Binnet & Hardley</pub_name>
<city>Washington</city>
<state>DC</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>1389</pub_id>
<pub_name>Algodata Infosystems</pub_name>
<city>Berkeley</city>
<state>CA</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>1622</pub_id>
<pub_name>Five Lakes Publishing</pub_name>
<city>Chicago</city>
<state>IL</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>1756</pub_id>
<pub_name>Ramona Publishers</pub_name>
<city>Dallas</city>
<state>TX</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>9901</pub_id>
<pub_name>GGG&G</pub_name>
<city>Muenchen</city>
<country>Germany</country>
  </Table>
  <Table>
<pub_id>9952</pub_id>
<pub_name>Scootney Books</pub_name>
<city>New York</city>
<state>NY</state>
<country>USA</country>
  </Table>
  <Table>
<pub_id>9999</pub_id>
<pub_name>Lucerne Publishing</pub_name>
<city>Paris</city>
<country>France</country>
  </Table>
</NewDataSet>