方法调用在 Android Studio 中突出显示错误 [英] Method invocation highlighed error in Android Studio

问题描述

我对 Android Studio 有点困惑.之前在Eclipse中没见过这种错误.

Im a little bit confused in Android Studio. I didint seen this kind of errors in Eclipse before.

示例:

    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction tf = fragmentManager.beginTransaction();
    Fragment oldFragment = fragmentManager.findFragmentByTag(AddDialogFragment.TAG);

这段代码工作正常，但是 fragmentManager.beginTransaction();被突出显示并说:方法调用 'fragmentManager.beginTransaction' 可能会产生更少的 'java.lang.NullPointerException'... (Ctrl+F1)

this code is working fine, but fragmentManager.beginTransaction(); gets highlighted and says: Method invocation 'fragmentManager.beginTransaction' may produce 'java.lang.NullPointerException' less... (Ctrl+F1)

此检查报告指定检查范围内始终为真或为假的那些条件，并根据代码的数据流分析指出可能抛出 RuntimeException 的位置.此检查还报告 Nullable/NotNull 合同违规.可以配置支持合约的注释(默认情况下将使用 annotations.jar 中的 @Nullable/@NotNull 注释)

This inspection reports those conditions in the specified inspection scope that are always true or false, as well as points out where a RuntimeException may be thrown, based on data flow analysis of the code. This inspection also reports Nullable/NotNull contract violations. Annotations to support the contract can be configured (by default @Nullable/@NotNull annotations from annotations.jar will be used)

我之前需要检查 Null 吗?

Do i have to check for Null before?

    FragmentManager fragmentManager = getFragmentManager();
    if(fragmentManager != null)
       FragmentTransaction tf = fragmentManager.beginTransaction();
    Fragment oldFragment = fragmentManager.findFragmentByTag(AddDialogFragment.TAG); 

我以前从未在任何 Tut 或 Example 中看到过这种情况.如果这是一个愚蠢的问题，那么抱歉，但我仍然是初学者:).

I have never seen this in any Tut or Example before. If this is a stupid question than sorry, but im still a beginner :) .

推荐答案

就我所见，Android Studio 对潜在的 NullPointerExceptions 显示了过多的警告，即使对于永远不会返回的方法空值.我只是忽略了其中的一些，但仔细检查所有这些很有用，因为有时我会错过一个重要的.

From what I've seen, Android Studio shows a bit too much warnings about potential NullPointerExceptions, even for methods that will never return null. I simply ignore some of them, but it's useful to carefully check all of them, because sometimes I missed an important one.

如果你查看 android 源代码，很容易看出 getFragmentManager() 永远不会返回 null :

If you look at the android source code, it's easy to see that getFragmentManager() will never return null :

public FragmentManager getFragmentManager() {
    return mFragments;
}

mFragments 在整个班级中只分配一次:

Where mFragments is assigned only once through the whole class :

final FragmentManagerImpl mFragments = new FragmentManagerImpl();

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