c# - 如何在调用其他构造函数之前抛出 ArgumentNullException

Question

我有一个关于构造函数的语法和在构造函数中抛出异常的问题。

如何在调用 CreateAnotherOne() 之前为参数 b 抛出 ArgumentNullException 并像在第二个构造函数中那样抛出异常而不在检查后复制代码？我可以将代码提取到一个单独的私有(private)方法中，但我需要从两个构造函数主体中调用它...是否有其他选项可以实现此目的？

public class MyClass
{
    public MyClass(IWhatEver a, ISomeThingElse b)
        : this(a, b != null ? b.CreateAnotherOne() : null)
    {
        // or should I call :this(a, b.CreateAnotherOne()) instead? this could cause a NullReferenceException => how to verify that b is not null?
        // don't want to call CallMeFromConstructor() instead of call to other constructor

        // would not do the following (why should I check a/c twice?) and the check is too late here (because already called a method on b, b.CreateAnotherOne())
        if (a == null)
        {
            throw new ArgumentNullException("a");
        }

        if (b == null)
        {
            throw new ArgumentNullException("b");
        }
    }

    public MyClass(IWhatEver c, IAnotherOne d)
    {
        if (c == null)
        {
            throw new ArgumentNullException("c");
        }
        if (d == null)
        {
            throw new ArgumentNullException("d");
        }

        // the cool code comes here, I could put it into
        // the CallMeFromConstructor method but is there another way?
    }
    ...

    private void CallMeFromConstructors()
    {
        // the cool code could be here, too (but is there another way?)
    }

如果我调用第二个构造函数: this(a, b != null ? b.CreateAnotherOne() : null) 我会得到一个 ArgumentNullException for d int 第二个构造函数。这对我来说听起来很奇怪并且可能会产生误导，因为我调用了第一个(只能在堆栈跟踪中看到它)。

问题是我不会写

:this(a, b == null ? b.CreateAnotherOne() : throw new ArgumentNullException("b"));

如果我将检查放入构造函数的主体，在这种情况下它会被检查到很晚。

有什么语法糖可以解决这个问题吗？

Answer 1

私有(private)方法可以做到这一点，但您也可以创建另一个私有(private)构造函数:

    private MyClass(IWhatEver a)
    {
        if (a == null)
        {
            throw new ArgumentNullException("a");
        }

        // the cool code comes here, I could put it into
        // the CallMeFromConstructor method but is there another way?
    }

    public MyClass(IWhatEver a, ISomeThingElse b) : this(a)
    {
        if (b == null)
        {
            throw new ArgumentNullException("b");
        }
    }

    public MyClass(IWhatEver a, IAnotherOne b) : this(a)
    {
        if (b == null)
        {
            throw new ArgumentNullException("b");
        }
    }