这是装饰者模式(将数据添加到对象)的一个示例吗？

Question

我需要向对象添加额外的数据-但我不需要添加功能。因此，下面的示例是经典的GOF Decorator模式吗？

class ClassIWantToDecorate
{
    public string GetData() { return "data"; }
}

class Decorator
{
    private ClassIWantToDecorate _classIWantToDecInstance = null;
    private string _additionalData;
    public Decorator(ClassIWantToDecorate classIWantToDec, string additionalData)
    {
        _classIWantToDecInstance = classIWantToDec;
        _additionalData = additionalData;
    }

    public string DataINeed()
    {
        return _classIWantToDecInstance.GetData();
    }

    public string AdditionalDataINeed()
    {
        return _additionalData;
    }
}

Answer 1

不是的。我会说这只是composition。

装饰器应该是这样的：

interface DataINeedProvider {
    string DataINeed();
}

class LoggingDecorator implements DataINeedProvider
{
    private DataINeedProvider _classIWantToDecInstance = null;
    private Logger logger = new Logger();
    public LoggingDecorator(DataINeedProvider classIWantToDec) {
        _classIWantToDecInstance = classIWantToDec;
    }

    public string DataINeed()
    {
        logger.log("DataINeed has been called");
        return _classIWantToDecInstance.DataINeed();
    }
}

PS:如果这不是有效的C#语法，很抱歉。我是一名Java开发人员。

Answer 2

您的实现的问题是您的装饰器接口与装饰器对象的接口不兼容。

有效的装饰器解决方案应该是：

interface ClassIWantToDecorateInterface {
  public string GetData();
}

class ClassIWantToDecorate implements ClassIWantToDecorateInterface {
    public string GetData() { return "data"; }
}

class Decorator implements ClassIWantToDecorateInterface {
    private ClassIWantToDecorateInterface _classIWantToDecInstance = null;
    private string _additionalData;
    public Decorator(ClassIWantToDecorateInterface classIWantToDec, string additionalData)
    {
        _classIWantToDecInstance = classIWantToDec;
        _additionalData = additionalData;
    }

    public string GetData() {
        return _classIWantToDecInstance.GetData();
    }

    public string AdditionalDataINeed() {
        return _additionalData;
    }
}

(我使用Java语法是因为我不确定您使用的是C#还是Java。根据语法，它可以是两者都是)