这发生在您在另一个线程中调用getActivity()时，该线程在片段被删除后结束。典型的情况是在HTTP请求完成时调用getActivity()(例如Toast)(例如onResponse)。

为了避免这种情况，您可以定义一个字段名mActivity，并使用它来代替getActivity()。该字段可以在Fragment的onAttach()方法中初始化，如下所示:

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    if (context instanceof Activity){
        mActivity =(Activity) context;
    }
}

在我的项目中，我通常用这个特性为我所有的Fragments定义一个基类:

public abstract class BaseFragment extends Fragment {

    protected FragmentActivity mActivity;

    @Override
public void onAttach(Context context) {
    super.onAttach(context);

    if (context instanceof Activity){
        mActivity =(Activity) context;
    }
}
}

快乐的编码,

另一个好的解决方案是使用Android的LiveData和MVVM架构。 你可以在你的ViewModel中定义一个LiveData对象，并在你的片段中观察它，当LiveData值发生变化时，只有当你的片段处于活动状态时，它才会通知你的观察者(在这种情况下是片段)，所以这将保证你的UI工作，只有当你的片段处于活动状态时才会访问活动。这是LiveData的一个优势

当然，当这个问题第一次被提出时，还没有LiveData。我把这个答案留在这里，因为在我看来，这个问题仍然存在，它可能会对某些人有所帮助。

在commit()之后调用回调函数的顺序:

无论你在commit()之后手动调用什么方法 onAttach () onCreateView () onActivityCreated ()

我需要做一些涉及一些视图的工作，所以onAttach()不适合我;它坠毁。所以我移动了我的代码的一部分，设置一些参数在一个方法调用后立即提交()(1.)，然后在onCreateView()(3.)内处理视图的代码的另一部分。

编写一个通用方法，确保永远不会得到空Activity。

public class BaseFragment extends Fragment {
    private Context contextNullSafe;

     @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
         /*View creation related to this fragment is finished here. So in case if contextNullSafe is null
         * then we can populate it here.In some discussion in - https://stackoverflow.com/questions/6215239/getactivity-returns-null-in-fragment-function
         * and https://stackoverflow.com/questions/47987649/why-getcontext-in-fragment-sometimes-returns-null,
         * there are some recommendations to call getContext() or getActivity() after onCreateView() and
         * onViewCreated() is called after the onCreateView() call every time */
        if (contextNullSafe == null) getContextNullSafety();
    }


   @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        contextNullSafe = context;
    }

    /**CALL THIS IF YOU NEED CONTEXT*/
    public Context getContextNullSafety() {
                if (getContext() != null) return getContext();
                if (getActivity() != null) return getActivity();
                if (contextNullSafe != null) return contextNullSafe;
                if (getView() != null && getView().getContext() != null) return getView().getContext();
                if (requireContext() != null) return requireContext();
                if (requireActivity() != null) return requireActivity();
                if (requireView() != null && requireView().getContext() != null)
                    return requireView().getContext();
                
                return null;
            
        }

    /**CALL THIS IF YOU NEED ACTIVITY*/
    public FragmentActivity getActivityNullSafety() {
        if (getContextNullSafety() != null && getContextNullSafety() instanceof FragmentActivity) {
            /*It is observed that if context it not null then it will be
             * the related host/container activity always*/
            return (FragmentActivity) getContextNullSafety();
        }
        return null;
    }

这发生在您在另一个线程中调用getActivity()时，该线程在片段被删除后结束。典型的情况是在HTTP请求完成时调用getActivity()(例如Toast)(例如onResponse)。

为了避免这种情况，您可以定义一个字段名mActivity，并使用它来代替getActivity()。该字段可以在Fragment的onAttach()方法中初始化，如下所示:

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    if (context instanceof Activity){
        mActivity =(Activity) context;
    }
}

在我的项目中，我通常用这个特性为我所有的Fragments定义一个基类:

public abstract class BaseFragment extends Fragment {

    protected FragmentActivity mActivity;

    @Override
public void onAttach(Context context) {
    super.onAttach(context);

    if (context instanceof Activity){
        mActivity =(Activity) context;
    }
}
}

快乐的编码,

The other answers that suggest keeping a reference to the activity in onAttach are just suggesting a bandaid to the real problem. When getActivity returns null it means that the Fragment is not attached to the Activity. Most commonly this happens when the Activity has gone away due to rotation or the Activity being finished but the Fragment still has some kind of callback listener registered preventing it from being garbage collected. When the listener gets called if you need to do something with the Activity but the Activity is gone there isn't much you can do. In your code you should just check getActivity() != null and if it's not there then don't do anything. If you keep a reference to the Activity that is gone you are preventing the Activity from being garbage collected. Any UI things you might try to do won't be seen by the user. I can imagine some situations where in the callback listener you want to have a Context for something non-UI related, in those cases it probably makes more sense to get the Application context. Note that the only reason that the onAttach trick isn't a big memory leak is because normally after the callback listener executes it won't be needed anymore and can be garbage collected along with the Fragment, all its View's and the Activity context. If you setRetainInstance(true) there is a bigger chance of a memory leak because the Activity field will also be retained but after rotation that could be the previous Activity not the current one.