在 C# 中如果不为 null 的方法调用

问题描述

是否可以以某种方式缩短此声明?

Is it possible to somehow shorten this statement?

if (obj != null)
    obj.SomeMethod();

因为我碰巧写了很多，这很烦人.我唯一能想到的就是实现Null Object模式，但这不是我每次都能做到的，当然也不是缩短语法的解决方案.

because I happen to write this a lot and it gets pretty annoying. The only thing I can think of is to implement Null Object pattern, but that's not what I can do every time and it's certainly not a solution to shorten syntax.

和事件类似的问题，其中

And similar problem with events, where

public event Func<string> MyEvent;

然后调用

if (MyEvent != null)
    MyEvent.Invoke();

推荐答案

从 C# 6 开始，您只需使用:

From C# 6 onwards, you can just use:

MyEvent?.Invoke();

或:

obj?.SomeMethod();

?. 是空值传播操作符，当操作数为null 时会导致.Invoke() 短路代码>.操作数只被访问一次，因此不存在检查和调用之间的值变化"问题的风险.

The ?. is the null-propagating operator, and will cause the .Invoke() to be short-circuited when the operand is null. The operand is only accessed once, so there is no risk of the "value changes between check and invoke" problem.

===

在 C# 6 之前，否:没有空安全魔法，只有一个例外；扩展方法 - 例如:

Prior to C# 6, no: there is no null-safe magic, with one exception; extension methods - for example:

public static void SafeInvoke(this Action action) {
    if(action != null) action();
}

现在这是有效的:

Action act = null;
act.SafeInvoke(); // does nothing
act = delegate {Console.WriteLine("hi");}
act.SafeInvoke(); // writes "hi"

在事件的情况下，这还具有消除竞争条件的优点，即您不需要临时变量.所以通常你需要:

In the case of events, this has the advantage of also removing the race-condition, i.e. you don't need a temporary variable. So normally you'd need:

var handler = SomeEvent;
if(handler != null) handler(this, EventArgs.Empty);

但带有:

public static void SafeInvoke(this EventHandler handler, object sender) {
    if(handler != null) handler(sender, EventArgs.Empty);
}

我们可以简单地使用:

SomeEvent.SafeInvoke(this); // no race condition, no null risk

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