在 onActivityCreated/onStart/onViewCreated 方法中 getView() 上的 NullPointerException 警告 [英] NullPointerException Warning on getView() inside onActivityCreated/onStart/onViewCreated method

问题描述

我知道 getView() 可能会在 onCreateView() 方法中返回 null，但即使我将下面的代码放入 onActivityCreated()、onStart() 或 onViewCreated() 方法，它仍然显示有关 Android Studio 中可能的 NullPointerException 的警告(尽管我的程序在没有任何问题).如何摆脱这个警告?

I know getView() might return null inside onCreateView() method, but even if I put the below code inside onActivityCreated(), onStart() or onViewCreated() methods, it still shows the warning about a possible NullPointerException in Android Studio (although my program runs without any issue). How to get rid of this warning?

我正在使用片段.

代码:

datpurchased = (EditText) getView().findViewById(R.id.datepurchased); 
//datpurchased defined as instance variable in the class

警告:

方法调用'getView().findViewById(R.id.datepurchased)'可能产生'java.lang.NullPointerException'

Method invocation 'getView().findViewById(R.id.datepurchased)' may produce 'java.lang.NullPointerException'

推荐答案

Android Studio 基于 IntelliJ IDEA，这是 IntelliJ 的一个特性，当您不检查由方法在使用前为null.

Android Studio is based on IntelliJ IDEA, and this is a feature of IntelliJ that gives you warnings at compile time when you are not checking if an object returned by a method is null before using it.

避免这种情况的一种方法是采用始终检查 null 或捕获 NullPointerException 风格的程序，但它会变得非常冗长，尤其是对于您知道总是会发生的事情返回一个对象并且永远不会null.

One way to avoid this is program in the style that always checks for null or catches NullPointerException, but it can get very verbose, especially for things you know will always return an object and never null.

另一种替代方法是使用诸如 @SuppressWarnings 之类的注释来抑制这种情况下的警告，用于使用您知道永远不能为空的对象的方法:

Another alternative is to suppress the warnings on such cases using annotations such as @SuppressWarnings for methods that use objects you know can never be null:

@SuppressWarnings({"NullableProblems"})
public Object myMethod(Object isNeverNull){
    return isNeverNull.classMethod();
}

或者，在您的情况下，是行级抑制:

or, in your case, a line-level suppression:

//noinspection NullableProblems
datpurchased = (EditText) getView().findViewById(R.id.datepurchased); //datpurchased defined as instance variable in the class

不过，请确保对象永远不能为空.

Be sure that the objects really can never be null, though.

可以在此处找到有关 IntelliJ 的 @NotNull 和 @Nullable 注释的更多信息，以及更多关于检查和抑制检查的信息这里.

More information on IntelliJ's @NotNull and @Nullable annotations can be found here, and more about inspections and supressing them here.

这篇关于在 onActivityCreated/onStart/onViewCreated 方法中 getView() 上的 NullPointerException 警告的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！