Android Studio错误的含义：未注释的参数覆盖@NonNull参数 [英] Meaning of Android Studio error: Not annotated parameter overrides @NonNull parameter

问题描述

我正在试用Android Studio。在创建一个新项目并添加一个默认的 onSaveInstanceState 方法到创建MyActivity类时，当我尝试提交代码到Git，我得到一个奇怪的错误，我不明白。代码如下：

我得到的错误是：

如果我尝试将方法签名更改为 protected void onSaveInstanceState（@NotNull Bundle outState），那么IDE会告诉我它无法解析符号 NotNull 。

解决方案

这是一个注释，但是正确的名字是 NonNull ：

  protected void onSaveInstanceState（@NonNull Bundle outState）
  

（以及）

  import android.support.annotation.NonNull; 
  

目的是允许编译器违反（例如方法的参数应该总是具有值，如在这种特定情况下，虽然有其他）。从支持注释文档：

@NonNull 注释可用于表示给定的参数
不能为空。

如果一个局部变量被认为是null（例如因为一些
更早的代码检查它是否为null），并将它作为
参数传递给一个方法标记为@NonNull，
IDE将警告您有可能的崩溃。

分析。运行时行为根本不会改变。

---

在这种情况下，特定的警告是，您覆盖的原始方法（ Activity ）在 outState @NonNull 注释>参数，但您没有将其包含在覆盖方法中。只需添加它应该解决这个问题，即

  @Override 
 protected void onSaveInstanceState（@NonNull Bundle outState）{
 super.onSaveInstanceState（outState）; 
} 
  

I'm trying out Android Studio. Upon creating a new project and adding a default onSaveInstanceState method to the create MyActivity class, when I try to commit the code to Git, I get a strange error I don't understand. The code is this:

The error I get is this:

If I try to change the method signature to protected void onSaveInstanceState(@NotNull Bundle outState), then the IDE tells me it can't resolve the symbol NotNull.

What do I need to do to get rid of the warning?

解决方案

It's an annotation, but the correct name is NonNull:

protected void onSaveInstanceState(@NonNull Bundle outState)

(And also)

import android.support.annotation.NonNull;

The purpose is to allow the compiler to warn when certain assumptions are being violated (such as a parameter of a method that should always have a value, as in this particular case, although there are others). From the Support Annotations documentation:

The @NonNull annotation can be used to indicate that a given parameter can not be null.

If a local variable is known to be null (for example because some earlier code checked whether it was null), and you pass that as a parameter to a method where that parameter is marked as @NonNull, the IDE will warn you that you have a potential crash.

They are tools for static analysis. Runtime behavior is not altered at all.

---

In this case, the particular warning is that the original method you're overriding (in Activity) has a @NonNull annotation on the outState parameter, but you did not include it in the overriding method. Just adding it should fix the issue, i.e.

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
}

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