ReadOnlyCollectionBase 类

定义

命名空间:
System.Collections
程序集:
mscorlib.dll, System.Collections.NonGeneric.dll
程序集:
mscorlib.dll
程序集:
netstandard.dll

abstract为强类型非泛型只读集合提供基类。

public ref class ReadOnlyCollectionBase abstract : System::Collections::ICollection
public abstract class ReadOnlyCollectionBase : System.Collections.ICollection
[System.Serializable]
public abstract class ReadOnlyCollectionBase : System.Collections.ICollection
[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public abstract class ReadOnlyCollectionBase : System.Collections.ICollection
type ReadOnlyCollectionBase = class
    interface ICollection
    interface IEnumerable
[<System.Serializable>]
type ReadOnlyCollectionBase = class
    interface ICollection
    interface IEnumerable
[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type ReadOnlyCollectionBase = class
    interface ICollection
    interface IEnumerable
Public MustInherit Class ReadOnlyCollectionBase
Implements ICollection
继承
Object
ReadOnlyCollectionBase
派生
属性
SerializableAttribute ComVisibleAttribute
实现
ICollection IEnumerable

示例

下面的代码示例实现该 ReadOnlyCollectionBase 类。

using System;
using System.Collections;

public class ROCollection : ReadOnlyCollectionBase  {

   public ROCollection( IList sourceList )  {
      InnerList.AddRange( sourceList );
   }

   public Object this[ int index ]  {
      get  {
         return( InnerList[index] );
      }
   }

   public int IndexOf( Object value )  {
      return( InnerList.IndexOf( value ) );
   }

   public bool Contains( Object value )  {
      return( InnerList.Contains( value ) );
   }
}

public class SamplesCollectionBase  {

   public static void Main()  {

      // Create an ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "red" );
      myAL.Add( "blue" );
      myAL.Add( "yellow" );
      myAL.Add( "green" );
      myAL.Add( "orange" );
      myAL.Add( "purple" );

      // Create a new ROCollection that contains the elements in myAL.
      ROCollection myCol = new ROCollection( myAL );

      // Display the contents of the collection using foreach. This is the preferred method.
      Console.WriteLine( "Contents of the collection (using foreach):" );
      PrintValues1( myCol );

      // Display the contents of the collection using the enumerator.
      Console.WriteLine( "Contents of the collection (using enumerator):" );
      PrintValues2( myCol );

      // Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine( "Contents of the collection (using Count and Item):" );
      PrintIndexAndValues( myCol );

      // Search the collection with Contains and IndexOf.
      Console.WriteLine( "Contains yellow: {0}", myCol.Contains( "yellow" ) );
      Console.WriteLine( "orange is at index {0}.", myCol.IndexOf( "orange" ) );
      Console.WriteLine();
   }

   // Uses the Count property and the Item property.
   public static void PrintIndexAndValues( ROCollection myCol )  {
      for ( int i = 0; i < myCol.Count; i++ )
         Console.WriteLine( "   [{0}]:   {1}", i, myCol[i] );
      Console.WriteLine();
   }

   // Uses the foreach statement which hides the complexity of the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintValues1( ROCollection myCol )  {
      foreach ( Object obj in myCol )
         Console.WriteLine( "   {0}", obj );
      Console.WriteLine();
   }

   // Uses the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintValues2( ROCollection myCol )  {
      System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "   {0}", myEnumerator.Current );
      Console.WriteLine();
   }
}


/*
This code produces the following output.

Contents of the collection (using foreach):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using enumerator):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using Count and Item):
   [0]:   red
   [1]:   blue
   [2]:   yellow
   [3]:   green
   [4]:   orange
   [5]:   purple

Contains yellow: True
orange is at index 4.

*/

Imports System.Collections

Public Class ROCollection
    Inherits ReadOnlyCollectionBase


    Public Sub New(sourceList As IList)
        InnerList.AddRange(sourceList)
    End Sub


    Default Public ReadOnly Property Item(index As Integer) As [Object]
        Get
            Return InnerList(index)
        End Get
    End Property


    Public Function IndexOf(value As [Object]) As Integer
        Return InnerList.IndexOf(value)
    End Function 'IndexOf


    Public Function Contains(value As [Object]) As Boolean
        Return InnerList.Contains(value)
    End Function 'Contains

End Class


Public Class SamplesCollectionBase

    Public Shared Sub Main()

        ' Create an ArrayList.
        Dim myAL As New ArrayList()
        myAL.Add("red")
        myAL.Add("blue")
        myAL.Add("yellow")
        myAL.Add("green")
        myAL.Add("orange")
        myAL.Add("purple")

        ' Create a new ROCollection that contains the elements in myAL.
        Dim myCol As New ROCollection(myAL)

        ' Display the contents of the collection using For Each. This is the preferred method.
        Console.WriteLine("Contents of the collection (using For Each):")
        PrintValues1(myCol)

        ' Display the contents of the collection using the enumerator.
        Console.WriteLine("Contents of the collection (using enumerator):")
        PrintValues2(myCol)

        ' Display the contents of the collection using the Count property and the Item property.
        Console.WriteLine("Contents of the collection (using Count and Item):")
        PrintIndexAndValues(myCol)

        ' Search the collection with Contains and IndexOf.
        Console.WriteLine("Contains yellow: {0}", myCol.Contains("yellow"))
        Console.WriteLine("orange is at index {0}.", myCol.IndexOf("orange"))
        Console.WriteLine()

    End Sub


    ' Uses the Count property and the Item property.
    Public Shared Sub PrintIndexAndValues(myCol As ROCollection)
        Dim i As Integer
        For i = 0 To myCol.Count - 1
            Console.WriteLine("   [{0}]:   {1}", i, myCol(i))
        Next i
        Console.WriteLine()
    End Sub


    ' Uses the For Each statement which hides the complexity of the enumerator.
    ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
    Public Shared Sub PrintValues1(myCol As ROCollection)
        Dim obj As [Object]
        For Each obj In  myCol
            Console.WriteLine("   {0}", obj)
        Next obj
        Console.WriteLine()
    End Sub


    ' Uses the enumerator. 
    ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
    Public Shared Sub PrintValues2(myCol As ROCollection)
        Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator()
        While myEnumerator.MoveNext()
            Console.WriteLine("   {0}", myEnumerator.Current)
        End While
        Console.WriteLine()
    End Sub

End Class


'This code produces the following output.
'
'Contents of the collection (using For Each):
'   red
'   blue
'   yellow
'   green
'   orange
'   purple
'
'Contents of the collection (using enumerator):
'   red
'   blue
'   yellow
'   green
'   orange
'   purple
'
'Contents of the collection (using Count and Item):
'   [0]:   red
'   [1]:   blue
'   [2]:   yellow
'   [3]:   green
'   [4]:   orange
'   [5]:   purple
'
'Contains yellow: True
'orange is at index 4.

注解

ReadOnlyCollectionBase实例始终为只读。 请参阅 CollectionBase 此类的可修改版本。

Important

不建议将 ReadOnlyCollectionBase 类用于新开发。 相反，我们建议使用泛型 ReadOnlyCollection<T> 类。 有关详细信息，请参阅不应在 GitHub 上使用 非泛型集合 。

实施者说明

提供了此基类，使实现者能够更轻松地创建强类型只读自定义集合。 鼓励实现者扩展此基类，而不是创建自己的基类。 此基类的成员受到保护，仅用于通过派生类使用。

此类使基础集合通过 InnerList 属性提供，该属性仅供直接派生自 ReadOnlyCollectionBase的类使用。 派生类必须确保其自己的用户无法修改基础集合。

构造函数

名称 说明
ReadOnlyCollectionBase()

初始化 ReadOnlyCollectionBase 类的新实例。

属性

名称 说明
Count

获取实例中包含的 ReadOnlyCollectionBase 元素数。
InnerList

获取实例中包含的 ReadOnlyCollectionBase 元素列表。

方法

名称 说明
Equals(Object)

确定指定的对象是否等于当前对象。

(继承自 Object)
GetEnumerator()

返回循环访问实例的 ReadOnlyCollectionBase 枚举数。
GetHashCode()

用作默认哈希函数。

(继承自 Object)
GetType()

获取当前实例的 Type。

(继承自 Object)
MemberwiseClone()

创建当前 Object的浅表副本。

(继承自 Object)
ToString()

返回一个表示当前对象的字符串。

(继承自 Object)

显式接口实现

名称 说明
ICollection.CopyTo(Array, Int32)

将整个 ReadOnlyCollectionBase 复制到兼容的一维 Array，从目标数组的指定索引处开始。
ICollection.IsSynchronized

获取一个值，该值指示是否同步对 ReadOnlyCollectionBase 对象的访问（线程安全）。
ICollection.SyncRoot

获取可用于同步对 ReadOnlyCollectionBase 对象的访问的对象。

扩展方法

名称 说明
AsParallel(IEnumerable)

启用查询的并行化。
AsQueryable(IEnumerable)

将 IEnumerable 转换为 IQueryable。
Cast<TResult>(IEnumerable)

将 IEnumerable 的元素强制转换为指定类型。
OfType<TResult>(IEnumerable)

根据指定类型筛选 IEnumerable 的元素。

适用于

线程安全性

此类型的公共静态（Shared 在 Visual Basic 中）成员是线程安全的。 不能保证任何实例成员是线程安全的。

此实现不提供同步的（线程安全）包装器ReadOnlyCollectionBase，但派生类可以创建其自己的使用属性的ReadOnlyCollectionBaseSyncRoot同步版本。

通过集合进行枚举本质上不是线程安全的过程。 即使集合同步，其他线程仍可以修改集合，这会导致枚举器引发异常。 若要保证枚举期间的线程安全性，可以在整个枚举期间锁定集合，也可以捕获由其他线程所做的更改导致的异常。

另请参阅