java - 从 RecyclerView 内的 onClickListener 启动 Activity 后出现 NullPointerException

Question

在 Fragment 中的 RecyclerView 内从 onClickListener 调用 startActivity 后，我在 logcat 中收到以下错误。

java.lang.NullPointerException
        at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
        at android.view.View.measure(View.java:15293)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:861)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:602)
        at android.view.View.measure(View.java:15293)

这会在创建其他 Activity (调用 OnCreate)后发生

这是Fragment的onViewCreated:

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    View view = getView();
    RecyclerView list = (RecyclerView) view.findViewById(R.id.list);

    list.setHasFixedSize(true);
    list.addItemDecoration(new DividerItemDecoration(getResources()));

    //Tried commenting out three of the following lines, no effect
    final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
    list.setLayoutManager(layoutManager);
    list.setItemAnimator(new DefaultItemAnimator());

    ArrayList<TimelineItem> timelineItems = new ArrayList<>();
    //populating the list with dummy data

    adapter = new TimelineAdapter(timelineItems);
    //this sets the onclick listener on the view inside the ViewHolder
    adapter.setPrimaryClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            openProfile();
        }
    });

    list.setAdapter(adapter);

openProfile 的代码:

public void openProfile(){
    Intent intent = new Intent(getActivity(), ProfileActivity.class);
    //NPE happens after this
    getActivity().startActivity(intent);
}

适配器代码:

@Override
public void onBindViewHolder(TimelineAdapter.ViewHolder viewHolder, int i) {
    TimelineItem timelineItem = dataSet.get(i);

    //bunch of findViewById

    secondaryAction.setOnClickListener(secondaryClickListener);
    textContent.setOnClickListener(primaryClickListener);
    avatar.setOnClickListener(primaryClickListener);
}

事实证明，当切换到新 Activity 时，总是会发生此错误。不特定于此 OnClickListener

Answer 1

可能 fragment 尚未附加到 Activity ，因此 getActivity() 返回 null。处理 fragment 时，最好重写 onAttach() 并从那里获取 Activity 的实例，以确保 fragment 已附加。