Question

我有一个抽象基类，它包含一些字段和一些作用于这些字段的方法。例如：

public abstract class A
{
    protected double _field;

    public double SquaredField { get { return _field * _field; } }

    ... some other abstract methods
}

我想在其构造函数中强加A初始化_field的所有子元素

public class B : A
{
    public B(double field)
    {
         _field = Math.Sqrt(field);
    }

    ... some other method implementations
}

实现这一目标的正确模式是什么？

- 编辑

我最终做的是：

public abstract class A
{
    protected readonly double _field;

    public A(double field)
    {
         _field = field;
    }

    public double SquaredField { get { return _field * _field; } }

    ... some other abstract methods
}


public class B : A
{
    public B(double field) : base(field)
    {
    }

    public static B CreateNew(double val)
    {
         return new B(Math.Sqrt(field));
    }

    ... some other method implementations
}

Answer 1

根本不要将字段公开给派生类。而是创建受保护的抽象属性：

public abstract class A
{
    protected double Field { get; }

    public double SquaredField { get { return Field * Field; } }
}

或者，如果字段对于特定实例应始终保持不变，请将其设为构造函数参数并将其保持为私有：

public abstract class A
{
    private readonly double _field;

    public double SquaredField { get { return _field * _field; } }

    protected A(double field)
    {
        _field = field;
    }
}

Answer 2

不要让类A具有无参数构造函数：

public abstract class A
{
    protected double _field;

    public double SquaredField { get { return _field * _field; } }

    // Require any fields that must be initialized in the base class's
    // constructor. If there are a lot of such fields, consider encapsulating
    // them all in their own class, e.g. AArgs.
    protected A(double field)
    {
        _field = field;
    }
}

public class B : A
{
    // You must call a base class constructor as below, because class A
    // no longer has a parameterless constructor to use by default.
    public B(double field)
        : base(field)
    {
    }
}

附录

如果无法在构造函数中进行初始化，则可以将该字段设置为抽象属性：

public abstract class A
{
    protected abstract double Field { get; }

    public double SquaredField { get { return Field * Field; } }
}

现在，派生类必须实现该属性，因此您可以为依赖的SquaredField属性做好准备。我会更改名称，因为它们不再是字段了。

Answer 3

这可能是一组字段比A本身更紧密耦合的信号，所以应该移到一个类，比如AParams。

然后在A中，您可以声明abstract protected AParams createParams()方法。

Answer 4

您可以使用单独的抽象函数来完成此任务。子类将被迫实现它。

public abstract class A
{
    protected double _field;

    protected A()
    {
        InitializeField();
    }

    protected abstract void InitializeField();

    public double SquaredField { get { return _field * _field; } }
}

public class B : A
{
    protected override void InitializeField()
    {
        // Initialize...
    }
}

强制子类初始化字段

4 个答案:

附录