DataTableReader.GetEnumerator 方法

定義

命名空間:

System.Data

組件:

System.Data.dll

回傳一個枚舉器，可用於遍歷項目集合。

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

一個 IEnumerator 代表物品集合的物件。

例外狀況

InvalidOperationException

嘗試讀取或存取封閉 DataTableReader.

範例

下列範例示範 GetEnumerator 方法的用法。 這包括列舉器在列啟動時從底層 DataTable 刪除時的行為。

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

程序會在主控台視窗顯示以下文字：

Peter
Mary
Russ

備註

列舉器僅允許讀取 中的資料 DataTableReader。 列舉器無法用來修改底層集合。

起初，列舉器會被放置在集合中的第一個元素之前。 在這個位置，叫喊 Current 會拋出例外。 因此，您必須先呼叫 MoveNext 列舉器先將列舉器推進到集合的第一個元素，再讀取 的 Current值。

Current 回傳一個 DbDataRecord，並返回相同的物件直到 MoveNext 被呼叫 或 Reset 。 MoveNext 設定 Current 為下一個元素。

當集合結束後，列舉器會被置於集合的最後一個元素之後，呼叫 MoveNext 則回傳 false。 如果最後一次呼叫回傳MoveNext，false呼叫Current會拋出例外。 此外，由於 僅 DataTableReader 提供前向存取，呼叫 Reset IEnumerator 的方法會拋 NotSupportedException出 。

提供 DataTableReader 穩定的列舉器。 這表示即使底層資料中發生了列刪除或新增，透過呼叫回 GetEnumerator 傳的列舉器仍然有效。