将此传递给基本构造函数

Question

我正在尝试为我正在编写的程序实现良好的设计模式。我有这样的类结构。

abstract class SomeBase
{
     public SomeObject obj { get; protected set; } 

     protected SomeBase(SomeObject x)
     {
           obj = x;
     }

     //Other methods and fields...
}

public class SomeDerived : SomeBase
{

     public SomeDerived() : base(new SomeObject(this))
     {

     }

}

现在我确定你知道，你不能在基础构造函数中传递它，因为此时对象还没有被初始化。无论如何，我真的希望有一个解决方法。让SomeDerived() 处理基类字段的设置对我来说不是最佳做法。我想将这个新对象向上传递。

Answer 1

这是不可能的，在构造函数之后使用Init方法：

 abstract class SomeBase
 {
      private SomeObject _obj { get; set; } 
      public SomeObject obj 
      {
           get 
           {    // check _obj is inited:
                if (_obj == null) throw new <exception of your choice> ;
                return _obj;
           } 
      }

      protected SomeBase()
      {
           obj = null;
      }

      protected void Init()
      {
           obj = x;
      }

      //Other methods and fields...
 }

 public class SomeDerived : SomeBase
 {

      public SomeDerived() : base()
      {
           Init(new SomeObject(this));
      }

 }

Answer 2

嗯，其实你在基础构造函数中就有了，所以不需要传递它。

using System;

abstract class SomeBase
{
    public SomeObject obj { get; protected set; }

    protected SomeBase()
    {
        // Will be executed as 1st step
        Console.WriteLine(1);

        // "this" here is SomeDerived object
        obj = new SomeObject((SomeDerived)this);
        // If you don`t like to depend upon SomeDerived type here,
        // you can do the same using the following line:
        //obj = (SomeObject)Activator.CreateInstance(typeof(SomeObject), this);
    }
}

class SomeObject
{
    public SomeObject(SomeDerived obj)
    {
        if (obj.obj == null)
        {
            // Will be executed as 2nd step
            Console.WriteLine(2);

            // You have the reference to SomeDerived here
            // But its properties are not yet initialized
            // (both SomeDerived and SomeBase constructors are in the progress)
            // So you should not access these properties 
            // in the SomeObject class constructor,
            // but you can do it in any method of SomeObject class 
            // (at the time the method will be called all constructors are finished).
        }
    }
}

class SomeDerived : SomeBase
{
    public SomeDerived()
    {
        // Will be executed as 3rd step
        Console.WriteLine(3);

        if (this.obj != null)
        {
            // You have the reference to SomeObject here,
            // which itself already got an access to SomeDerived reference
        }
    }
}

class MainClass 
{
    public static void Main (string[] args) 
    {
        var instance = new SomeDerived();
        Console.WriteLine (instance.obj); // Outputs SomeObject
    }
}

https://repl.it/@Konard/LinenZealousBlockchain

另一种解决方案是使用 lambda 表达式，因此 SomeDerived 类将完全控制对它的引用如何传递给 SomeObject。

using System;

abstract class SomeBase
{
    public SomeObject obj { get; protected set; }

    protected SomeBase(Func<SomeBase, SomeObject> someObjectInitilizer)
    {
        // Will be executed as 1st step
        Console.WriteLine(1);

        // "this" here is SomeDerived object
        obj = someObjectInitilizer(this);
    }
}

class SomeObject
{
    public SomeObject(SomeDerived obj)
    {
        if (obj.obj == null)
        {
            // Will be executed as 2nd step
            Console.WriteLine(2);

            // You have the reference to SomeDerived here
            // But its properties are not yet initialized
            // (both SomeDerived and SomeBase constructors are in the progress)
            // So you should not access these properties 
            // in the SomeObject class constructor,
            // but you can do it in any method of SomeObject class 
            // (at the time the method will be called all constructors are finished).
        }
    }
}

class SomeDerived : SomeBase
{
    public SomeDerived() : base((@this) => new SomeObject((SomeDerived)@this))
    {
        // Will be executed as 3rd step
        Console.WriteLine(3);

        if (this.obj != null)
        {
            // You have the reference to SomeObject here,
            // which itself already got an access to SomeDerived reference
        }
    }
}

class MainClass 
{
    public static void Main (string[] args) 
    {
        var instance = new SomeDerived();
        Console.WriteLine (instance.obj); // Outputs SomeObject
    }
}

https://repl.it/@Konard/ParchedYellowgreenType

Answer 3

1) 构造函数的设计完全是错误的——它看起来像实例方法，但实际上它是半实例方法的半方法。

2）“具有模式的良好设计程序”不会导致聚合中的类之间立即出现循环依赖，正如我们在此处看到的那样 - 两个类必须在创建时相互了解和使用（！！！）谁知道 SomeObject 对“this " 在它的构造函数中？？？

所以在“模式”中存在两个问题 - 类之间的高度依赖和初始化逻辑的不可用封装。所以我们必须找到“模式”的方式来解决它……嗯……怎么办……

在你提供的代码中，我看到派生类只是为属性 obj 提供了它自己的逻辑 您可以将其重写为自动初始化属性

public abstract class MyClass{
     private SomeObject _obj ; 
     public SomeObject Obj {get { return  _obj ?? (_obj = InitializeObj() );}} //no setter needed
     protected abstract SomeObject InitializeObj();
}

public class MyRealClass:MyClass {
    protected override SomeObject InitializeObj(){
        return new VerySpecialSomeObject(this, other, another, 1, 2 , false, option: new Options());
    }   
}

对于您的示例，此类解决方案提供了获胜的单一“模式”-“多态性”））并获得额外的奖励-如果“Obj”没有用-它永远不会被创建））））