問題描述

是否可以以某種方式縮短此聲明?

Is it possible to somehow shorten this statement?

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

因為我碰巧寫了很多，這很煩人.我唯一能想到的就是實現Null Object模式，但這不是我每次都能做到的，當然也不是縮短語法的解決方案.

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.

和事件類似的問題，其中

And similar problem with events, where

public event Func<string> MyEvent;

然后調用

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

推薦答案

從 C# 6 開始，您只需使用:

From C# 6 onwards, you can just use:

MyEvent?.Invoke();

或:

obj?.SomeMethod();

?. 是空值傳播操作符，當操作數為null 時會導致.Invoke() 短路代碼>.操作數只被訪問一次，因此不存在檢查和調用之間的值變化"問題的風險.

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:沒有空安全魔法，只有一個例外；擴展方法 - 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();
}

現在這是有效的:

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

在事件的情況下，這還具有消除競爭條件的優點，即您不需要臨時變量.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);

但帶有:

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

我們可以簡單地使用:

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

這篇關于在 C# 中如果不為 null 的方法調用的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！