SqlParameterCollection.GetEnumerator 方法

定義

命名空間:

System.Data.SqlClient

組件:

System.Data.dll

回傳一個遍歷 的 SqlParameterCollection枚舉子。

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

A IEnumerator 代表 SqlParameterCollection。

範例

以下程式碼範例展示了自訂集合介面的實作 IEnumerable 。 在此範例中，GetEnumerator未明確呼叫，但實作以支援 （foreachFor Each在 Visual Basic 中）。 此程式碼範例是介面更大範例 IEnumerable 的一部分。

using System;
using System.Collections;

// Simple business object.
public class Person
{
    public Person(string fName, string lName)
    {
        this.firstName = fName;
        this.lastName = lName;
    }

    public string firstName;
    public string lastName;
}

// Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
public class People : IEnumerable
{
    private Person[] _people;
    public People(Person[] pArray)
    {
        _people = new Person[pArray.Length];

        for (int i = 0; i < pArray.Length; i++)
        {
            _people[i] = pArray[i];
        }
    }

// Implementation for the GetEnumerator method.
    IEnumerator IEnumerable.GetEnumerator()
    {
       return (IEnumerator) GetEnumerator();
    }

    public PeopleEnum GetEnumerator()
    {
        return new PeopleEnum(_people);
    }
}

// When you implement IEnumerable, you must also implement IEnumerator.
public class PeopleEnum : IEnumerator
{
    public Person[] _people;

    // Enumerators are positioned before the first element
    // until the first MoveNext() call.
    int position = -1;

    public PeopleEnum(Person[] list)
    {
        _people = list;
    }

    public bool MoveNext()
    {
        position++;
        return (position < _people.Length);
    }

    public void Reset()
    {
        position = -1;
    }

    object IEnumerator.Current
    {
        get
        {
            return Current;
        }
    }

    public Person Current
    {
        get
        {
            try
            {
                return _people[position];
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }
}

class App
{
    static void Main()
    {
        Person[] peopleArray = new Person[3]
        {
            new Person("John", "Smith"),
            new Person("Jim", "Johnson"),
            new Person("Sue", "Rabon"),
        };

        People peopleList = new People(peopleArray);
        foreach (Person p in peopleList)
            Console.WriteLine(p.firstName + " " + p.lastName);
    }
}

/* This code produces output similar to the following:
 *
 * John Smith
 * Jim Johnson
 * Sue Rabon
 *
 */

Imports System.Collections

' Simple business object.
Public Class Person

    Public Sub New(ByVal fName As String, ByVal lName As String)
        Me.firstName = fName
        Me.lastName = lName
    End Sub


    Public firstName As String
    Public lastName As String
End Class

' Collection of Person objects, which implements IEnumerable so that
' it can be used with ForEach syntax.
Public Class People
    Implements IEnumerable

    Private _people() As Person

    Public Sub New(ByVal pArray() As Person)
        _people = New Person(pArray.Length - 1) {}

        Dim i As Integer
        For i = 0 To pArray.Length - 1
            _people(i) = pArray(i)
        Next i
    End Sub

    ' Implementation of GetEnumerator.
    Public Function GetEnumerator() As IEnumerator _
      Implements IEnumerable.GetEnumerator

        Return New PeopleEnum(_people)
    End Function

End Class

' When you implement IEnumerable, you must also implement IEnumerator.
Public Class PeopleEnum
    Implements IEnumerator

    Public _people() As Person

    ' Enumerators are positioned before the first element
    ' until the first MoveNext() call.
    Dim position As Integer = -1

    Public Sub New(ByVal list() As Person)
        _people = list
    End Sub

    Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
        position = position + 1
        Return (position < _people.Length)
    End Function

    Public Sub Reset() Implements IEnumerator.Reset
        position = -1
    End Sub

    Public ReadOnly Property Current() As Object Implements IEnumerator.Current
        Get
            Try
                Return _people(position)
            Catch ex As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property
End Class

Class App
    Shared Sub Main()
        Dim peopleArray() As Person = { _
            New Person("John", "Smith"), _
            New Person("Jim", "Johnson"), _
            New Person("Sue", "Rabon")}

        Dim peopleList As New People(peopleArray)
        Dim p As Person
        For Each p In peopleList
            Console.WriteLine(p.firstName + " " + p.lastName)
        Next

    End Sub
End Class

' This code produces output similar to the following:
' 
' John Smith
' Jim Johnson
' Sue Rabon

備註

此成員為明確介面成員實作。 它只能在實 SqlParameterCollection 例投射到 IEnumerable 介面時使用。

foreach C# 語言（For Each在 Visual Basic 中）的陳述隱藏了列舉器的複雜度。 因此，建議使用 foreach ，而非直接操作列舉器。

列舉器可用於讀取集合中的資料，但無法用來修改底層集合。

最初，列舉器會被放置在集合中的第一個元素之前。 此 Reset 方法也會將調查員拉回此位置。 在此位置，該 Current 性質尚未定義。 因此，你必須呼叫 MoveNext 方法，將列舉子推進到集合的第一個元素，才能讀取 的 Current值。

Current 回傳相同物件，直到被呼叫其中一 MoveNext 或 Reset 。 MoveNext 設定 Current 為下一個元素。

若 MoveNext 通過集合的末尾，列舉器會位於集合的最後一個元素之後，並 MoveNext 返回 false。 當列舉器處於此位置時，後續呼叫 MoveNext 也返回 false。 若最後一次呼叫 MoveNext 返回 false， Current 則未定義。 若要再次設定 Current 為集合的第一個元素，你可以呼叫 Reset ，接著 MoveNext。

若對集合進行變更，例如新增、修改或刪除元素，列舉器的行為則未定義。

列舉員並非擁有收藏的獨家存取權;因此，透過集合列舉本質上並非執行緒安全的程序。 為了確保列舉時執行緒的安全，你可以在整個列舉過程中鎖定該集合。 為了讓多個執行緒都能存取該集合進行讀寫，你必須實作自己的同步功能。

另請參閱

• 指令與參數（ADO.NET）
• DataAdapter 參數（ADO.NET）
• 使用 .NET Framework 資料提供者用於 SQL Server
• ADO.NET 概觀