Android列表视图不适用于片段
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【中文标题】Android列表视图不适用于片段【英文标题】：Android List view not working with fragment 【发布时间】：2021-10-31 09:31:51 【问题描述】：我正在尝试使用片段和 Recycler View Adapter 显示图像视图列表。
我每次都会遇到这个异常
Process: com.example.plasmavietiles, PID: 4860
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.recyclerview.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference
at androidx.recyclerview.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:4311)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4045)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3849)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:148)
at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:43)
at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1892)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:918)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:726)
at android.view.View.layout(View.java:17637)
at android.view.ViewGroup.layout(ViewGroup.java:5575)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2346)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2068)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
at android.view.Choreographer.doCallbacks(Choreographer.java:686)
at android.view.Choreographer.doFrame(Choreographer.java:621)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
这是我的代码：
问卷调查
public class QuestionnaireActivity extends Activity implements View.OnClickListener, View.OnTouchListener
private ArrayList<Integer> questionList;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_questionnaire);
/*Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);*/
prepareView();
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
QuestionFragment question = new QuestionFragment();
question.setQuestionArray(questionList);
fragmentTransaction.replace(R.id.questionnaireFragment,question);
fragmentTransaction.commit();
@Override
protected void attachBaseContext(Context base)
super.attachBaseContext(LocalHelper.wrap(base));
@SuppressLint("ClickableViewAccessibility")
private void prepareView()
this.questionList = new ArrayList<>();
Random r = new Random();
int tmp;
for(int i =0 ;i<5;)
tmp = r.nextInt((20 - 1) + 1) + 1;
if(!this.questionList.contains(tmp))
this.questionList.add(tmp);
i++;
问题片段类：
public class QuestionFragment extends Fragment
// TODO: Customize parameter argument names
private static final String ARG_COLUMN_COUNT = "column-count";
// TODO: Customize parameters
private int mColumnCount = 1;
List<Integer> questionArray = new ArrayList<>();
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public QuestionFragment()
public void setQuestionArray(List<Integer> questionArray)
this.questionArray = questionArray;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
/* if (getArguments() != null)
mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
*/
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
View view = inflater.inflate(R.layout.fragment_question_list, container, false);
// Set the adapter
if (view instanceof RecyclerView)
Context context = view.getContext();
RecyclerView recyclerView = (RecyclerView) view;
if (mColumnCount <= 1)
recyclerView.setLayoutManager(new LinearLayoutManager(context));
else
recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
recyclerView.setAdapter(new MyQuestionRecyclerViewAdapter(questionArray));
return view;
我的 Recycler 视图适配器类：
public class MyQuestionRecyclerViewAdapter extends RecyclerView.Adapter<MyQuestionRecyclerViewAdapter.ViewHolder>
private final List<Integer> mValues;
public MyQuestionRecyclerViewAdapter(List<Integer> items)
mValues = items;
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.fragment_question, parent, false);
return new ViewHolder(view);
@Override
public void onBindViewHolder(final ViewHolder holder, int position)
// holder.mItem = mValues.get(position);
// holder.mIdView.setText(mValues.get(position).id);
holder.mContentView.setImageResource(R.drawable.facebook_icon);
@Override
public int getItemCount()
return mValues.size();
public class ViewHolder extends RecyclerView.ViewHolder
public final ImageView mContentView;
public ViewHolder(View view)
super(view);
//mIdView = (TextView) view.findViewById(R.id.item_number);
mContentView = (ImageView) view.findViewById(R.id.imageView10);
【问题讨论】：
【参考方案1】：你可能想交换这些布局
之前的片段类
View view = inflater.inflate(R.layout.fragment_question_list, container, false);
之前的适配器类
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.fragment_question, parent, false);
之后的片段类
View view = inflater.inflate(R.layout.fragment_question, container, false);
之后的适配器类
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.fragment_question_l8st, parent, false);
【讨论】：
【参考方案2】：不要检查view是否为instanceof recyclerview，而是直接通过id查找recyclerview。
RecyclerView recycler_view = view.findViewById(R.id.recyclerViewId);
Context context = view.getContext();
RecyclerView recyclerView = (RecyclerView) view;
if (mColumnCount <= 1)
recyclerView.setLayoutManager(new LinearLayoutManager(context));
else
recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
recyclerView.setAdapter(new MyQuestionRecyclerViewAdapter(questionArray));
【讨论】：
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