CA1819：属性不应返回数组

项目
08/12/2011

类型名	PropertiesShouldNotReturnArrays
CheckId	CA1819
类别	Microsoft.Performance
是否重大更改	是

原因

公共类型中的公共或受保护属性返回一个数组。

规则说明

即使属性是只读的，该属性返回的数组也不是写保护的。若要使数组不会被更改，属性必须返回数组的副本。通常，用户不能理解调用这种属性的负面性能影响。特别是，他们可能将该属性用作索引属性。

如何解决冲突

若要修复与该规则的冲突，请将属性更改为方法，或将属性更改为返回一个集合。

何时禁止显示警告

特性可以包含返回数组的属性，但不能包含返回集合的属性。可以禁止显示从 [System.Attribute] 类派生的特性的属性所引发的警告。否则，不要禁止显示此规则发出的警告。

冲突的示例

说明

下面的示例演示一个与该规则冲突的属性。

代码

Imports System 

Namespace PerformanceLibrary     

    Public Class Book         

        Private _Pages As String()       

        Public Sub New(ByVal pages As String())  
            _Pages = pages        
        End Sub         

        Public ReadOnly Property Pages() As String()            
            Get                
                Return _Pages            
            End Get            
        End Property     

    End Class 

End Namespace

using System; 

namespace PerformanceLibrary
{    
    public class Book    
    {        
        private string[] _Pages;      

        public Book(string[] pages)        
        {            
            _Pages = pages;        
        }         

        public string[] Pages        
        {            
            get { return _Pages; }        
        }    
    }
}

注释

若要修复与该规则的冲突，请将属性更改为方法，或将属性更改为返回一个集合而不是数组。

将属性更改为方法的示例

说明

下面的示例通过将属性更改为方法来修复冲突。

代码

Imports System 

Namespace PerformanceLibrary     

    Public Class Book         

        Private _Pages As String()         

        Public Sub New(ByVal pages As String())            
            _Pages = pages        
        End Sub         

        Public Function GetPages() As String()      
            ' Need to return a clone of the array so that consumers            
            ' of this library cannot change its contents            
            Return DirectCast(_Pages.Clone(), String())        
        End Function     

    End Class 

End Namespace

using System; 

namespace PerformanceLibrary
{    
    public class Book    
    {        
        private string[] _Pages;         

        public Book(string[] pages)        
        {            
            _Pages = pages;        
        }         

        public string[] GetPages()        
        {            
            // Need to return a clone of the array so that consumers            
            // of this library cannot change its contents            
            return (string[])_Pages.Clone();        
        }    
    }
}

返回集合的示例。

说明

下面的示例通过以下方法修复冲突：将属性更改为返回一个

ReadOnlyCollection.

代码

Imports System
Imports System.Collections.ObjectModel 

Namespace PerformanceLibrary     

    Public Class Book         

        Private _Pages As ReadOnlyCollection(Of String)         

        Public Sub New(ByVal pages As String())            
            _Pages = New ReadOnlyCollection(Of String)(pages)        
        End Sub         

        Public ReadOnly Property Pages() As ReadOnlyCollection(Of String)            
            Get                
                Return _Pages            
            End Get        
        End Property     

    End Class 

End Namespace

using System;
using System.Collections.ObjectModel; 

namespace PerformanceLibrary
{    
    public class Book    
    {        
        private ReadOnlyCollection<string> _Pages;         
        public Book(string[] pages)        
        {            
            _Pages = new ReadOnlyCollection<string>(pages);        
        }         

        public ReadOnlyCollection<string> Pages        
        {            
            get { return _Pages; }        
        }    
    }
}

允许用户修改属性

说明

您可能希望允许类的使用者修改属性。下面的示例演示一个与该规则冲突的读/写属性。

代码

Imports System 

Namespace PerformanceLibrary     

    Public Class Book         

        Private _Pages As String()         

        Public Sub New(ByVal pages As String())            
            _Pages = pages        
        End Sub         

        Public Property Pages() As String()            
            Get                
                Return _Pages            
            End Get            

            Set(ByVal value as String())                
                _Pages = value            
            End Set        
        End Property     

    End Class 

End Namespace

using System; 

namespace PerformanceLibrary
{    
    public class Book    
    {        
        private string[] _Pages;         

        public Book(string[] pages)        
        {            
            _Pages = pages;        
        }         

        public string[] Pages        
        {            
            get { return _Pages; }            
            set { _Pages = value; }        
        }    
    }
}

注释

下面的示例通过将属性更改为返回一个 Collection 来修复冲突。

代码

Imports System
Imports System.Collections.ObjectModel 

Namespace PerformanceLibrary     

    Public Class Book         

        Private _Pages As Collection(Of String)         

        Public Sub New(ByVal pages As String())            
            _Pages = New Collection(Of String)(pages)        
        End Sub         

        Public ReadOnly Property Pages() As Collection(Of String)            
            Get                
                Return _Pages            
            End Get        
        End Property     

    End Class 

End Namespace

using System;
using System.Collections.ObjectModel; 

namespace PerformanceLibrary
{    
    public class Book    
    {        
        private Collection<string> _Pages;         

        public Book(string[] pages)        
        {            
            _Pages = new Collection<string>(pages);        
        }         

        public Collection<string> Pages        
        {            
            get { return _Pages; }        
        }    
    }
}

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