学步园

基本操作: 创建一个具有一个列和五个行的 DataTable。创建两个 DataView 对象，并针对每个对象设置 RowStateFilter 以显示表数据的不同视图。然后打印这些值。

Private Sub DemonstrateDataView() 
   ’ Create one DataTable with one column. 
   Dim myTable As DataTable = New DataTable("myTable") 
   Dim colItem As DataColumn = New DataColumn("item", Type.GetType("System.String")) 
   myTable.Columns.Add(colItem) 
   ’ Add five items. 
   Dim NewRow As DataRow 
   Dim i As Integer 
   For i = 0 To 4 

      NewRow = myTable.NewRow() 
      NewRow("item") = "Item " & i 
      myTable.Rows.Add(NewRow) 
   Next 
   myTable.AcceptChanges() 
   ’ Create two DataView objects with the same table. 
   Dim firstView As DataView = New DataView(myTable) 
   Dim secondView As DataView = New DataView(myTable) 

   ’ Change the values in the table. 
   myTable.Rows(0)("item") = "cat" 
   myTable.Rows(1)("item") = "dog" 

   ’ Print current table values. 
   PrintTableOrView(myTable, "Current Values in Table") 
     
   ’ Set first DataView to show only modified versions of original rows. 
   firstView.RowStateFilter = DataViewRowState.ModifiedOriginal 
   ’ Print values.     
   PrintTableOrView(firstView, "First DataView: ModifiedOriginal") 
   ’ Add one New row to the second view. 
   Dim myDataRowView As DataRowView 
   myDataRowView = secondView.AddNew() 
   myDataRowView("item") = "fish" 
   ’ Set second DataView to show modified versions of current rows, or New rows. 
   secondView.RowStateFilter = DataViewRowState.ModifiedCurrent Or DataViewRowState.Added 
   ’ Print modified and Added rows. 
   PrintTableOrView(secondView, "Second DataView: ModifiedCurrent or Added") 
End Sub 

Overloads Private Sub PrintTableOrView(ByVal dv As DataView, ByVal label As String) 
   Console.WriteLine(label) 
   Dim i As Integer 
   For i = 0 To dv.count - 1 

      Console.WriteLine(dv(i)("item")) 
   Next 
   Console.WriteLine() 
End Sub 

Overloads Private Sub PrintTableOrView(ByVal t As DataTable, ByVal label As String) 
   Console.WriteLine(label) 
   Dim i As Integer 
   For i = 0 To t.Rows.Count - 1 
      Console.WriteLine(t.Rows(i)("item")) 
   Next 
   Console.WriteLine() 
End Sub 

缓存 DataSet, 操作时使用 DataView 对数据进行筛选:

Private Sub MakeDataView() 
   Dim dv As DataView 
   dv = New DataView 
   With dv 
      .Table = DataSet1.Tables("Suppliers") 
      .AllowDelete = True 
      .AllowEdit = True 
      .AllowNew = True 
      .RowFilter = "City = ’Berlin’" 
      .RowStateFilter = DataViewRowState.ModifiedCurrent 
      .Sort = "CompanyName DESC" 
   End With 
    
   ’ Simple bind to a TextBox control 
   Text1.DataBindings.Add("Text", dv, "CompanyName") 
End Sub