SqlParameterCollection.GetEnumerator 方法

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

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

public override System.Collections.IEnumerator GetEnumerator();

public System.Collections.IEnumerator GetEnumerator();

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

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

Public Overrides Function GetEnumerator () As IEnumerator

Public Function GetEnumerator () As IEnumerator

返回

IEnumerator 的一个 SqlParameterCollection。

实现

示例

下面的代码示例演示自定义集合接口 IEnumerable 的实现。 在此示例中， GetEnumerator 未显式调用 ，但实现它以支持在 Visual Basic) 中使用 foreach (For Each 。 此代码示例是 接口的较大示例的 IEnumerable 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

注解

此成员是显式接口成员的实现。 它只能在 SqlParameterCollection 实例被强制转换为 IEnumerable 接口时使用。

C# 语言的 foreach 语句（在 Visual Basic 中为 For Each）隐藏了枚举数的复杂性。 因此，建议使用 foreach，而不是直接操作枚举数。

枚举器可用于读取集合中的数据，但不能用于修改基础集合。

最初，枚举数定位在集合中第一个元素的前面。 方法 Reset 还会将枚举器带回此位置。 在此位置， Current 属性未定义。 因此，在读取 的值Current之前，必须调用 MoveNext 方法以将枚举器推进到集合的第一个元素。

在调用 Current 或 MoveNext 之前，Reset 返回同一对象。 MoveNext 将 Current 设置为下一个元素。

如果 MoveNext 传递集合的末尾，则枚举器位于集合中的最后一个元素之后，并 MoveNext 返回 false。 当枚举器位于此位置时，对 MoveNext 的后续调用也会返回 false。 如果最后一次调用 MoveNext 返回 false， Current 则为未定义。 若要再次将 Current 设置为集合的第一个元素，可以调用 Reset 并接着调用 MoveNext。

如果对集合进行了更改（例如添加、修改或删除元素），则枚举器的行为是未定义的。

枚举数没有对集合的独占访问权；因此，从头到尾对一个集合进行枚举在本质上不是一个线程安全的过程。 若要确保枚举过程中的线程安全性，可以在整个枚举过程中锁定集合。 若要允许多个线程访问集合以进行读写操作，则必须实现自己的同步。

另请参阅

• 命令和参数 (ADO.NET)
• DataAdapter 参数 (ADO.NET)
• 使用适用于 SQL Server 的 .NET Framework 数据提供程序
• ADO.NET 概述