无法从firebase数据库获取数据

l3zydbqr  于 2021-09-13  发布在  Java
关注(0)|答案(0)|浏览(291)

我正在创建一个应用程序，现在我正在使用recyclerview显示存储在firebase数据库中的所有用户帖子。但我有一个问题，当程序从名为location、title和days的字符串接收数据时，会抛出空指针异常。您可以在下面看到代码：
后内容：

  1. public class PostContent {
  2.     String days, description, difficulty, imageUri, kilometers, location, map, nickname,
  3.     time, title, uid;
  5.     Long numOfImages;
  7.     public PostContent()
  8.     {
  9.     }
  11.     public PostContent(String days, String description, String difficulty, String imageUri, String kilometers, String location, String map, String nickname, String time, String title, String uid, Long numOfImages) {
  12.         this.days = days;
  13.         this.description = description;
  14.         this.difficulty = difficulty;
  15.         this.imageUri = imageUri;
  16.         this.kilometers = kilometers;
  17.         this.location = location;
  18.         this.map = map;
  19.         this.nickname = nickname;
  20.         this.time = time;
  21.         this.title = title;
  22.         this.uid = uid;
  23.         this.numOfImages = numOfImages;
  24.     }
  26.     public String getDays() {
  27.         return days;
  28.     }
  30.     public void setDays(String days) {
  31.         this.days = days;
  32.     }
  34.     public String getDescription() {
  35.         return description;
  36.     }
  38.     public void setDescription(String description) {
  39.         this.description = description;
  40.     }
  42.     public String getDifficulty() {
  43.         return difficulty;
  44.     }
  46.     public void setDifficulty(String difficulty) {
  47.         this.difficulty = difficulty;
  48.     }
  50.     public String getImageUri() {
  51.         return imageUri;
  52.     }
  54.     public void setImageUri(String imageUri) {
  55.         this.imageUri = imageUri;
  56.     }
  58.     public String getKilometers() {
  59.         return kilometers;
  60.     }
  62.     public void setKilometers(String kilometers) {
  63.         this.kilometers = kilometers;
  64.     }
  66.     public String getLocation() {
  67.         return location;
  68.     }
  70.     public void setLocation(String location) {
  71.         this.location = location;
  72.     }
  74.     public String getMap() {
  75.         return map;
  76.     }
  78.     public void setMap(String map) {
  79.         this.map = map;
  80.     }
  82.     public String getNickname() {
  83.         return nickname;
  84.     }
  86.     public void setNickname(String nickname) {
  87.         this.nickname = nickname;
  88.     }
  90.     public String getTime() {
  91.         return time;
  92.     }
  94.     public void setTime(String time) {
  95.         this.time = time;
  96.     }
  98.     public String getTitle() {
  99.         return title;
  100.     }
  102.     public void setTitle(String title) {
  103.         this.title = title;
  104.     }
  106.     public String getUid() {
  107.         return uid;
  108.     }
  110.     public void setUid(String uid) {
  111.         this.uid = uid;
  112.     }
  114.     public Long getNumOfImages() {
  115.         return numOfImages;
  116.     }
  118.     public void setNumOfImages(Long numOfImages) {
  119.         this.numOfImages = numOfImages;
  120.     }

postsadapter：在这里您可以看到注解掉的代码，因为从数据库接收数据时问题就出现在这些行中

  1. public class PostAdapter extends FirebaseRecyclerAdapter<PostContent, PostAdapter.postsViewHolder> {
  2.     private Context mContext;
  4.     public PostAdapter(FirebaseRecyclerOptions<PostContent> options) {
  5.         super(options);
  6.     }
  8.     @Override
  9.     protected void onBindViewHolder(@NonNull PostAdapter.postsViewHolder holder, int position, @NonNull PostContent model) {
  10.         holder.nickname.setText(model.getNickname());
  11.         holder.country.setText(model.getLocation());
  12.         //holder.title.setText(model.getTitle());
  13.         //holder.days.setText(model.getDays());
  14.         holder.difficulty.setText(model.getDifficulty());
  15.         //holder.kilometers.setText(model.getKilometers());
  16.         holder.description.setText(model.getDescription());
  17.         Picasso.get().load(model.getImageUri()).into(holder.avatarUri);
  19.     }
  21.     @NonNull
  22.     @Override
  23.     public PostAdapter.postsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
  24.         View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.posts, parent, false);
  25.         return new PostAdapter.postsViewHolder(view);
  26.     }
  28.     class postsViewHolder extends  RecyclerView.ViewHolder
  29.     {
  30.         CircleImageView avatarUri;
  31.         TextView nickname, country, title, days, difficulty, likesNum, kilometers,description;
  32.         SliderView mSliderView;
  33.         ImageView likes, comments, save;
  34.         ImageButton more;
  36.         public postsViewHolder(@NonNull View view)
  37.         {
  38.             super(view);
  40.             avatarUri = view.findViewById(R.id.post_profile_picture);
  41.             nickname = view.findViewById(R.id.post_nickname);
  42.             country = view.findViewById(R.id.post_country);
  43.             title = view.findViewById(R.id.post_title);
  44.             days = view.findViewById(R.id.post_days);
  45.             difficulty = view.findViewById(R.id.post_difficulty);
  46.             mSliderView = view.findViewById(R.id.images_posts);
  47.             likes = view.findViewById(R.id.post_likes);
  48.             comments = view.findViewById(R.id.post_comments);
  49.             save = view.findViewById(R.id.post_save);
  50.             likesNum = view.findViewById(R.id.post_likes_number);
  51.             description = view.findViewById(R.id.post_description);
  52.             more = view.findViewById(R.id.post_more);
  53.             kilometers = view.findViewById(R.id.post_distance);
  54.         }
  55.     }
  56. }

homefragment：

  1. public class HomeFragment extends Fragment {
  3.     private RecyclerView mRecyclerView;
  4.     private Context mContext;
  5.     private FirebaseMethods mFirebaseMethods;
  6.     private List<PostContent> mPostContentList;
  7.     private PostAdapter mPostAdapter;
  8.     private DatabaseReference postRef;
  9.     private FirebaseAuth mAuth;
  10.     private String currentUserID;
  12.     public HomeFragment() {
  14.     }
  16.     public static HomeFragment newInstance(String param1, String param2) {
  17.         HomeFragment fragment = new HomeFragment();
  18.         Bundle args = new Bundle();
  19.         fragment.setArguments(args);
  20.         return fragment;
  21.     }
  23.     @Override
  24.     public void onCreate(Bundle savedInstanceState) {
  25.         super.onCreate(savedInstanceState);
  27.     }
  29.     @Override
  30.     public View onCreateView(LayoutInflater inflater, ViewGroup container,
  31.                              Bundle savedInstanceState) {
  32.         View view = inflater.inflate(R.layout.fragment_home, container, false);
  34.         mContext = container.getContext();
  35.         mFirebaseMethods = new FirebaseMethods(mContext);
  36.         mRecyclerView = view.findViewById(R.id.posts_recycler);
  37.         DatabaseReference postRef = FirebaseDatabase.getInstance().getReference("Posts");
  39.         postRef = FirebaseDatabase.getInstance().getReference().child("Posts");
  40.         mRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
  42.         FirebaseRecyclerOptions options =
  43.                 new FirebaseRecyclerOptions.Builder<PostContent>()
  44.                 .setQuery(FirebaseDatabase.getInstance().getReference().child("Posts"), PostContent.class)
  45.                 .build();
  47.         mPostAdapter = new PostAdapter(options);
  48.         mRecyclerView.setAdapter(mPostAdapter);
  50.         return view;
  51.     }
  53.     @Override
  54.     public void onStart() {
  55.         super.onStart();
  56.         mPostAdapter.startListening();
  57.     }
  59.     @Override
  60.     public void onStop() {
  61.         super.onStop();
  62.         mPostAdapter.stopListening();
  63.     }
  64. }

firebase数据库：
结构
日志：

  1. Process: com.company.android.myapplication, PID: 6989
  2.     java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
  3.         at com.company.android.myapplication.PostAdapter.onBindViewHolder(PostAdapter.java:41)
  4.         at com.company.android.myapplication.PostAdapter.onBindViewHolder(PostAdapter.java:28)
  5.         at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:149)
  6.         at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
  7.         at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
  8.         at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
  9.         at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
  10.         at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
  11.         at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
  12.         at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
  13.         at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
  14.         at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
  15.         at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
  16.         at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
  17.         at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
  18.         at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
  19.         at android.view.View.layout(View.java:22114)
  20.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  21.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:334)
  22.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  23.         at android.view.View.layout(View.java:22114)
  24.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  25.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:334)
  26.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  27.         at android.view.View.layout(View.java:22114)
  28.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  29.         at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1855)
  30.         at android.view.View.layout(View.java:22114)
  31.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  32.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:334)
  33.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  34.         at android.view.View.layout(View.java:22114)
  35.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  36.         at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1839)
  37.         at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1683)
  38.         at android.widget.LinearLayout.onLayout(LinearLayout.java:1592)
  39.         at android.view.View.layout(View.java:22114)
  40.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  41.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:334)
  42.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  43.         at android.view.View.layout(View.java:22114)
  44.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  45.         at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1839)
  46.         at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1683)
  47.         at android.widget.LinearLayout.onLayout(LinearLayout.java:1592)
  48.         at android.view.View.layout(View.java:22114)
  49.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  50.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:334)
  51.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  52.         at com.android.internal.policy.DecorView.onLayout(DecorView.java:937)
  53.         at android.view.View.layout(View.java:22114)
  54.         at android.view.ViewGroup.layout(ViewGroup.java:6335)
  55.         at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3282)
  56. 2021-07-27 16:08:54.344 6989-6989/com.company.android.myapplication E/AndroidRuntime:     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2782)
  57.         at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1854)
  58.         at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8086)
  59.         at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1057)
  60.         at android.view.Choreographer.doCallbacks(Choreographer.java:875)
  61.         at android.view.Choreographer.doFrame(Choreographer.java:776)
  62.         at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1042)
  63.         at android.os.Handler.handleCallback(Handler.java:888)
  64.         at android.os.Handler.dispatchMessage(Handler.java:100)
  65.         at android.os.Looper.loop(Looper.java:213)
  66.         at android.app.ActivityThread.main(ActivityThread.java:8178)
  67.         at java.lang.reflect.Method.invoke(Native Method)
  68.         at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
  69.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101)
JavaNullPointerException

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