在 Android Studio 中使用 @NonNull 注解的正确方法

2022-01-13 00:00:00 annotations android java non-nullable

我想在 Android 中使用 @NonNull 注释，但我想不出正确的方法.我建议你这个例子:

I'd like to use the @NonNull annotation in Android, but I can't figure out just the right way to do it. I propose you this example:

public void doStuff(@NonNull String s){
     //do work with s...    
}

所以当我调用 doStuff(null) 时，IDE 会给我一个警告.问题是我不能依赖这个注释，因为像 this 问题指出，它们不会传播很远.所以我想对我的方法进行空检查，如下所示:

So when i call doStuff(null) the IDE will give me a warning. The problem is that I cannot rely on this annotation since, like this question points out, they don't propagate very far. So I'd like to put a null check on my method, like this:

 if(s==null) throw new IllegalAgrumentException();

但假设 s!=null 的 IDE 会警告我 s==null 始终为假.我想知道最好的方法是什么.

But the IDE, assuming that s!=null, will warn me that s==null is always false. I'd like to know what is the best way to do this.

我个人认为应该有一个像 @ShouldntBeNull 这样的注解 only 检查并警告 null 没有传递给它，但 没有 在检查值为 null 时会报错.

I personally think that there should be an annotation like @ShouldntBeNull that only checks and warns that null isn't passed to it, but doesn't complains when the value is null checked.

推荐答案

你可以使用Objects.requireNonNull 为此.它将在内部进行检查(因此 IDE 不会在您的函数上显示警告)并引发 NullPointerException 当参数为null:

You can use Objects.requireNonNull for that. It will do the check internally (so the IDE will not show a warning on your function) and raise a NullPointerException when the parameter is null:

public MyMethod(@NonNull Context pContext) {
    Objects.requireNonNull(pContext);
    ...
}

如果你想抛出另一个异常或使用 API 级别 <19，然后你可以只做你自己的助手类来实现同样的检查.例如

If you want to throw another exception or use API level < 19, then you can just make your own helper-class to implement the same check. e.g.

public class Check {
    public static <T> T requireNonNull(T obj) {
        if (obj == null)
            throw new IllegalArgumentException();
        return obj;
    }
}

并像这样使用它:

public MyMethod(@NonNull Context pContext) {
    Check.requireNonNull(pContext);
    ...
}

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