在 C# 中，是否有一种干净的方法来检查多个级别的空引用

发布于 2024-09-19 10:54:07 字数 255 浏览 7 评论 0原文

例如，如果我想调用以下内容： person.Head.Nose.Sniff() 那么，如果我想安全，我必须执行以下操作：

if(person != null)
    if(person.Head != null)
        if(person.Head.Nose != null)
            person.Head.Nose.Sniff();

有没有更简单的方法来制定这个表达式？

原文

For example, if I want to call the following:
person.Head.Nose.Sniff()
then, if I want to be safe, I have to do the following:

if(person != null)
    if(person.Head != null)
        if(person.Head.Nose != null)
            person.Head.Nose.Sniff();

Is there any easier way of formulating this expression?

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似最初 2024-09-26 10:54:07

首先，您可以利用布尔逻辑运算符中的短路并执行以下操作：

if (person != null && person.Head != null && person.Head.Nose != null)
{
    person.Head.Nose.Sniff();
}

另请注意，您所做的事情违反了开发软件的设计指南，该指南称为德墨忒尔定律。

First you can take advantage of short-circuiting in the boolean logic operators and do something like:

if (person != null && person.Head != null && person.Head.Nose != null)
{
    person.Head.Nose.Sniff();
}

Also note that what you are doing goes against a design guideline for developing software that is known as Law of Demeter.

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幽梦紫曦～ 2024-09-26 10:54:07

有没有更简单的方法来表达这个表达式？

在 C# 6 中，您可以使用 null 条件运算符 ？。

代码示例

这是打包到方法中的原始代码，并假设 Sniff() 始终返回 true：

    public bool PerformNullCheckVersion1(Person person)
    {
        if (person != null)
            if (person.Head != null)
                if (person.Head.Nose != null)
                    return person.Head.Nose.Sniff();
        return false;
    }

这是使用 C# 6 null 条件运算符重写的代码：

    public bool PerformNullCheckVersion2(Person person)
    {
        return person?.Head?.Nose?.Sniff() ?? false;
    }

< code>?? 是空合并运算符且与你的问题无关。

有关完整示例，请参阅：
https://github.com/lernkurve/Stackoverflow-question-3701563

Is there any easier way of formulating this expression?

With C# 6, you can use the null-conditional operator ?.

Code example

This is your original code packed into a method and assuming Sniff() always returns true:

    public bool PerformNullCheckVersion1(Person person)
    {
        if (person != null)
            if (person.Head != null)
                if (person.Head.Nose != null)
                    return person.Head.Nose.Sniff();
        return false;
    }

This is your code rewritten with the C# 6 null-conditional operator:

    public bool PerformNullCheckVersion2(Person person)
    {
        return person?.Head?.Nose?.Sniff() ?? false;
    }

The ?? is the null-coalescing operator and is not related to your question.

For the full example, see:
https://github.com/lernkurve/Stackoverflow-question-3701563

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玉环 2024-09-26 10:54:07

这是沿着同样提到的流畅参数验证的另一个实现：链式 null 检查和 Maybe monad

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没企图 2024-09-26 10:54:07

其实也不是，除此之外

 if (person != null && person.Head != null && person.Head.Nose != null)

Not really, besides

 if (person != null && person.Head != null && person.Head.Nose != null)

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把人绕傻吧 2024-09-26 10:54:07

您可以使用空对象而不是空值。如果调用链中的任何对象是空对象，则 Sniff 将不执行任何操作。

这不会引发异常：

person.Head.Nose.Sniff();

您的 null 类可能如下所示（您也可以将它们用作单例，并具有 IPerson、IHead 和 INose 的接口code>)：

class NullPerson : Person {
  public override Head Head { get { return new NullHead(); }
}
class NullHead : Head {
  public override Nose Nose { get { return new NullNose(); }
}
class NullNose : Nose {
  public override void Sniff() { /* no-op */ }
}

顺便说一句，在 Oxygene 中，有一个运算符用于此目的：

person:Head:Nose:Sniff;

You could use null objects instead of null values. Sniff would then do nothing if any objects in the call chain are null objects.

This would not throw an exception:

person.Head.Nose.Sniff();

Your null classes could look like this (you could also use them as singletons and have interfaces for IPerson, IHead and INose):

class NullPerson : Person {
  public override Head Head { get { return new NullHead(); }
}
class NullHead : Head {
  public override Nose Nose { get { return new NullNose(); }
}
class NullNose : Nose {
  public override void Sniff() { /* no-op */ }
}

As a side note, in Oxygene there's an operator for this:

person:Head:Nose:Sniff;

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一桥轻雨一伞开 2024-09-26 10:54:07

您可以使用Fluent参数验证< /a>

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滥情稳全场 2024-09-26 10:54:07

最好的方法是使用 && 运算符而不是嵌套的 if 语句：

if (person != null && person.Head != null && person.Head.Nose != null)
{
    person.Head.Nose.Sniff();
}

请注意，从技术上讲，您可以执行类似的 null 检查使用表达式树。你的方法将有一个像这样的签名：

static bool IsNotNull<T>(Expression<Func<T>> expression);

...这将允许你编写看起来像这样的代码：

if (IsNotNull(() => person.Head.Nose))
{
    person.Head.Nose.Sniff();
}

但这将涉及反射，并且与 < 相比，通常更难以以任何深入的方式遵循code>&& 方法。

The best way is just to use the && operator instead of nested if statements:

if (person != null && person.Head != null && person.Head.Nose != null)
{
    person.Head.Nose.Sniff();
}

Note that you technically could perform a similar null check using an expression tree. Your method would have a signature like this:

static bool IsNotNull<T>(Expression<Func<T>> expression);

...which would allow you to write code looking something like this:

if (IsNotNull(() => person.Head.Nose))
{
    person.Head.Nose.Sniff();
}

But this would involve reflection and would generally be much more difficult to follow in any sort of in-depth way compared to the && method.

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盗梦空间 2024-09-26 10:54:07

if (person?.Head?.Nose != null) person.Head.Nose.Sniff();

if (person?.Head?.Nose != null) person.Head.Nose.Sniff();

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本王不退位尔等都是臣 2024-09-26 10:54:07

我会摆脱对 null 的任何使用，并执行如下操作：

((Nose)person.BodyParts[BodyPart.Nose]).Sniff();

这将需要某种基本的类或接口。

public abstract class BodyPart
{
    public bool IsDecapitated { get; private set; }

    public BodyPart(bool isDecapitated)
    {
        IsDecapitated = isDecapitated;
    } 
}

I would get rid of any use of null and do something like this:

((Nose)person.BodyParts[BodyPart.Nose]).Sniff();

This would require some kind of base class or interface.

public abstract class BodyPart
{
    public bool IsDecapitated { get; private set; }

    public BodyPart(bool isDecapitated)
    {
        IsDecapitated = isDecapitated;
    } 
}

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