考虑将基类型作为参数传递

更新：2007 年 11 月

原因

某方法声明包含一个派生类型的形参，且该方法仅调用该参数的基类型的成员。

规则说明

在方法声明中将基类型指定为参数时，可以将派生自基类型的任何类型作为相应的变量传递给方法。在方法体中使用该变量时，所执行的特定方法取决于该变量的类型。如果不需要派生类型提供的其他功能，则使用基类型可允许更广泛地使用方法。

如何修复冲突

要修复与该规则的冲突，请将参数的类型更改为其基类型。

何时禁止显示警告

如果方法需要派生类型提供的特定功能，或者强制仅仅将该派生类型或另一个派生类型传递给方法，则可以安全地禁止显示此规则发出的警告。在这种情况下，代码将更为可靠，因为编译器和运行库会提供强类型检查。

示例

下面的示例演示与该规则冲突的方法 ManipulateFileStream，此方法只能与 FileStream 对象一起使用。第二个方法 ManipulateAnyStream 将 FileStream 参数替换为 Stream，从而满足该规则。

Imports System
Imports System.IO

Namespace DesignLibrary

    Public Class StreamUser

        Sub ManipulateFileStream(ByVal stream As IO.FileStream)
            If stream Is Nothing Then Throw New ArgumentNullException("stream")

            Dim anInteger As Integer = stream.ReadByte()
            While (anInteger <> -1)
                ' Do something.
                anInteger = stream.ReadByte()
            End While
        End Sub

        Sub ManipulateAnyStream(ByVal anyStream As IO.Stream)
            If anyStream Is Nothing Then Throw New ArgumentNullException("anyStream")

            Dim anInteger As Integer = anyStream.ReadByte()
            While (anInteger <> -1)
                ' Do something.
                anInteger = anyStream.ReadByte()
            End While
        End Sub
    End Class


   Public Class TestStreams

      Shared Sub Main()
            Dim someStreamUser As New StreamUser()
            Dim testFileStream As New FileStream( _
               "test.dat", FileMode.OpenOrCreate)
            Dim testMemoryStream As New MemoryStream(New Byte() {})

            ' Cannot be used with testMemoryStream.
            someStreamUser.ManipulateFileStream(testFileStream)
            someStreamUser.ManipulateAnyStream(testFileStream)
            someStreamUser.ManipulateAnyStream(testMemoryStream)
            testFileStream.Close()
        End Sub
   End Class
End Namespace

using System;
using System.IO;

namespace DesignLibrary
{
    public class StreamUser
    {
        int anInteger;

        public void ManipulateFileStream(FileStream stream)
        {
            while ((anInteger = stream.ReadByte()) != -1)
            {
                // Do something.
            }
        }

        public void ManipulateAnyStream(Stream anyStream)
        {
            while ((anInteger = anyStream.ReadByte()) != -1)
            {
                // Do something.
            }
        }
    }

    class TestStreams
    {
        static void Main()
        {
            StreamUser someStreamUser = new StreamUser();
            MemoryStream testMemoryStream = new MemoryStream(new byte[] { });
            using (FileStream testFileStream =
                     new FileStream("test.dat", FileMode.OpenOrCreate))
            {
                // Cannot be used with testMemoryStream.
                someStreamUser.ManipulateFileStream(testFileStream);

                someStreamUser.ManipulateAnyStream(testFileStream);
                someStreamUser.ManipulateAnyStream(testMemoryStream);
            }
        }
    }
}

using namespace System;
using namespace System::IO;

namespace DesignLibrary
{
   public ref class StreamUser
   {
      int anInteger;

   public:
      void ManipulateFileStream(FileStream^ stream)
      {
         while((anInteger = stream->ReadByte()) != -1)
         {
            // Do something.
         }
      }

      void ManipulateAnyStream(Stream^ anyStream)
      {
         while((anInteger = anyStream->ReadByte()) != -1)
         {
            // Do something.
         }
      }
   };
}

using namespace DesignLibrary;

static void main()
{
   StreamUser^ someStreamUser = gcnew StreamUser();
   FileStream^ testFileStream = 
      gcnew FileStream("test.dat", FileMode::OpenOrCreate);
   MemoryStream^ testMemoryStream = 
      gcnew MemoryStream(gcnew array<Byte>{});

   // Cannot be used with testMemoryStream.
   someStreamUser->ManipulateFileStream(testFileStream);

   someStreamUser->ManipulateAnyStream(testFileStream);
   someStreamUser->ManipulateAnyStream(testMemoryStream);

   testFileStream->Close();
}

相关规则

成员不应公开某些具体类型