DataTableReader.GetEnumerator 方法

public:
 override System::Collections::IEnumerator ^ GetEnumerator();

public override System.Collections.IEnumerator GetEnumerator ();

override this.GetEnumerator : unit -> System.Collections.IEnumerator

Public Overrides Function GetEnumerator () As IEnumerator

傳回

IEnumerator 物件，表示項目集合。

例外狀況

範例

下列範例示範 GetEnumerator 方法的用法。 這包括列舉值在使用中時從基礎 DataTable 刪除數據列時，列舉值的行為。

public static void Main()
{
    try
    {
        DataTable userTable = new DataTable("peopleTable");

        userTable.Columns.Add("Id", typeof(int));
        userTable.Columns.Add("Name", typeof(string));

        // Note that even if you create the DataTableReader
        // before adding the rows, the enumerator can still
        // visit all the rows.
        DataTableReader reader = userTable.CreateDataReader();
        userTable.Rows.Add(new object[] { 1, "Peter" });
        userTable.Rows.Add(new object[] { 2, "Mary" });
        userTable.Rows.Add(new object[] { 3, "Andy" });
        userTable.Rows.Add(new object[] { 4, "Russ" });

        IEnumerator enumerator = reader.GetEnumerator();
        // Keep track of whether the row to be deleted
        // has actually been deleted yet. This allows
        // this sample to demonstrate that the enumerator
        // is able to survive row deletion.
        bool isRowDeleted = false;
        while (enumerator.MoveNext())
        {
            DbDataRecord dataRecord = (DbDataRecord)enumerator.Current;

            // While the enumerator is active, delete a row.
            // This doesn't affect the behavior of the enumerator.
            if (!isRowDeleted)
            {
                isRowDeleted = true;
                userTable.Rows[2].Delete();
            }
            Console.WriteLine(dataRecord.GetString(1));
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex);
    }
    Console.ReadLine();
}

Sub Main()
   Try
      Dim userTable As New DataTable("peopleTable")
      userTable.Columns.Add("Id", GetType(Integer))
      userTable.Columns.Add("Name", GetType(String))

      ' Note that even if you create the DataTableReader
      ' before adding the rows, the enumerator can still
      ' visit all the rows.
      Dim reader As DataTableReader = userTable.CreateDataReader()
      userTable.Rows.Add(1, "Peter")
      userTable.Rows.Add(2, "Mary")
      userTable.Rows.Add(3, "Andy")
      userTable.Rows.Add(4, "Russ")

      Dim enumerator As IEnumerator = reader.GetEnumerator()
      ' Keep track of whether the row to be deleted
      ' has actually been deleted yet. This allows
      ' this sample to demonstrate that the enumerator
      ' is able to survive row deletion.
      Dim isRowDeleted As Boolean = False
      While (enumerator.MoveNext())

         Dim dataRecord As DbDataRecord = CType(enumerator.Current, _
             DbDataRecord)

         ' While the enumerator is active, delete a row.
         ' This doesn't affect the behavior of the enumerator.
         If Not isRowDeleted Then
            isRowDeleted = True
            userTable.Rows(2).Delete()
         End If
         Console.WriteLine(dataRecord.GetString(1))
      End While
   Catch ex As Exception

      Console.WriteLine(ex)
   End Try
   Console.ReadLine()
End Sub

此程式會在主控台視窗中顯示下列文字：

Peter  
Mary  
Russ  

備註

列舉值只允許讀取 中的數據 DataTableReader。 列舉值無法用來修改基礎集合。

一開始，列舉值位於集合中的第一個專案之前。 在這個位置，呼叫 Current 會擲回例外狀況。 因此，在讀取 MoveNext 的值之前，必須呼叫 Current 以將列舉值前移至集合的第一個項目。

Current 會傳 DbDataRecord回 ，並傳回相同的物件，直到 MoveNext 呼叫 或 Reset 為止。 MoveNext 會將 Current 設定為下一個項目。

傳遞集合結尾之後，列舉值會放在集合的最後一個項目之後，而呼叫 MoveNext 會傳回 false。 如果最後一 MoveNext 次呼叫傳 false回 ，則呼叫 Current 會擲回例外狀況。 此外，由於提供 DataTableReader 其數據的順向存取權，因此呼叫 Reset IEnumerator 的 方法會 NotSupportedException擲回 。

提供 DataTableReader 穩定的列舉值。 這表示即使在基礎數據中發生數據列刪除或新增，呼叫 GetEnumerator 所傳回的枚舉器仍然有效。

適用於