知识大全 ASP.NET ViewState 初探

Posted 2022-07-17 知

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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 > <H > 在 ViewState 中存储非控件状态 </H > <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= DataGrid runat= server OnSortCommand= SortGrid BorderStyle= None BorderWidth= px BorderColor= #CCCCCC BackColor= White CellPadding= AllowSorting= True > <HeaderStyle Font Bold= True ForeColor= White BackColor= # > </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( )) 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 DataGrid DataSource = dv DataGrid DataBind() End Sub Private Sub SortGrid(sender As Object e As DataGridSortCommandEventArgs) DataGrid CurrentPageIndex = 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 > <H > 在 ViewState 中存储非控件状态 </H > <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= DataGrid runat= server OnSortCommand= SortGrid BorderStyle= None BorderWidth= px BorderColor= #CCCCCC BackColor= White CellPadding= AllowSorting= True > <HeaderStyle Font Bold= True ForeColor= White BackColor= # > </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[ ]); // 应用排序过滤器和方向 dv Sort = SortField; if (!SortAscending) dv Sort += DESC ; // 绑定网格 DataGrid DataSource = dv; DataGrid DataBind(); void SortGrid(object sender DataGridSortCommandEventArgs e) DataGrid CurrentPageIndex = ; 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= standalone= yes ?> <NewDataSet> <Table> <pub_id> </pub_id> <pub_name>New Moon Books</pub_name> <city>Boston</city> <state>MA</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Binnet & Hardley</pub_name> <city>Washington</city> <state>DC</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Algodata Infosystems</pub_name> <city>Berkeley</city> <state>CA</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Five Lakes Publishing</pub_name> <city>Chicago</city> <state>IL</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Ramona Publishers</pub_name> <city>Dallas</city> <state>TX</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>GGG&G</pub_name> <city>Muenchen</city> <country>Germany</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Scootney Books</pub_name> <city>New York</city> <state>NY</state> <country>USA</country> </Table> <Table> <pub_id> </pub_id> <pub_name>Lucerne Publishing</pub_name> <city>Paris</city> <country>France</country> </Table> </NewDataSet> cha138/Article/program/net/201311/12702