覆盖属性以使它们只读 - 那么setter呢？

Question

我在类层次结构中有以下设计目标:

有BaseClass一些定义的属性,通常是读/写:

public class Media
{
    public virtual object Content { get; set; }
    public virtual double recordingLength { get; set; }
}

目的是有一些子类,其中此属性现在是只读的:

public class CompactDisk : Media
{
    public override object Content
    { 
        get { return this.getContent(); }
        set { 
               // THERE SHOULDN'T BE A SETTER 
            }
    }

    public override double recordingLength
    { 
        get { return 74; }
        set { 
               // NO SETTER EITHER HERE!
            }
    }
}

我迷失在这里,因为我不知道应该如何实现我的设计意图.

Answer 1

一种可能的方法是使用接口.

您可以将基本概念拆分为两个界面:

public interface IWritableMedia
{
    object Content { set; }
    double recordingLength { set; }
}

public interface IReadOnlyMedia
{
    object Content { get; }
    double recordingLength { get; }
}

然后CompactDisk应该只实现IReadOnlyMedia:

public class CompactDisk : IReadOnlyMedia
{
    public object Content { get { return ......; } }
    public double recordingLength { get { return .......; } }
}

如果要实现CD-RW(可重写),则应实现两个接口:

public class RewritableCompactDisk : IReadOnlyMedia, IWritableMedia
{
    public object Content { get; set; }
    public double recordingLength { get; set; }
}

这样您可以将变量键入为:IReadOnlyMedia或IWritableMedia:

IReadOnlyMedia media = new CompactDisk();
IWritableMedia media2 = new RewritableCompactDisk();

现在问题是IWritableMedia没有提供getter而你不想声明另一个类型的变量IReadOnlyMedia.解决方案是设计第三个接口, IReadWriteMedia并且RewritableCompactDisk应该实现它:

public interface IReadWriteMedia : IReadOnlyMedia, IWritableMedia
{
}

public class RewritableCompactDisk : IReadWriteMedia
{
    public object Content { get; set; }
    public double recordingLength { get; set; }
}

由于IReadWriteMedia实现了IReadOnlyMedia和IWritableMedia,现在您可以使用IReadWriteMedia键入变量并访问getter和setter:

IReadWriteMedia media3 = new RewritableCompactDisk();
object content = media3.Content;
media3.Content = "hello world";