java - findViewById() 可能会产生 NullPointerException

Question

我有很多这样的电话:

(ListView) getView().findViewById(R.id.main_list_view);
(TextView) getView().findViewById(R.id.items_no);
....

AndroidStudio 告诉我他们可能会产生一个NullPointerException:

Method invocation getView().findViewById(R.id.main_list_view) may produce java.lang.NullPointerException less... (Ctrl+F1)

This inspection analyzes method control and data flow to report possible conditions that are always true or false, expressions whose value is statically proven to be constant, and situations that can lead to nullability contract violations.

Variables, method parameters and return values marked as @Nullable or @NotNull are treated as nullable (or not-null, respectively) and used during the analysis to check nullability contracts, e.g. report possible NullPointerException errors.

More complex contracts can be defined using @Contract annotation, for example:

@Contract("_, null -> null") — method returns null if its second argument is null @Contract("_, null -> null; _, !null -> !null") — method returns null if its second argument is null and not-null otherwise

@Contract("true -> fail") — a typical assertFalse method which throws an exception if true is passed to it

The inspection can be configured to use custom @Nullable @NotNull annotations (by default the ones from annotations.jar will be used)

幸运的是一切正常，但是我可以对这段代码进行改进吗？

Answer 1

这是 android.support.v7.app.AppCompatActivity 中的一个已知问题，已在 v24 中修复。

https://code.google.com/p/android/issues/detail?id=203345

android.support.v4.app.FragmentActivity 或 android.app.Activity 不会有任何问题