3

我有一个与构造函数的语法和在构造函数中抛出异常有关的问题。

如何在调用 CreateAnotherOne() 之前为参数 b 抛出 ArgumentNullException 并在第二个构造函数中抛出异常，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方法中，但我需要从两个构造函数主体中调用它......还有其他选择来实现这一点吗？

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?)
    }

如果我用 : this(a, b != null ? b.CreateAnotherOne() : null) 调用第二个构造函数，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）。

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中，在这种情况下它会被检查到很晚。

任何语法糖的想法来解决这个问题？

4

1 回答 1

3

私有方法可以做到这一点，但您也可以创建另一个私有构造函数：

    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");
        }
    }
于 2013-01-31T18:22:14.003 回答