How can i fix this error retrieving data from firebase-CodePudding

'E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.pahalunitedfoundation, PID: 31028
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.pahalunitedfoundation.mainModel
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:436)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
    at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
    at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:29)
    at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:15)
    at com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot(BaseCachingSnapshotParser.java:36)
    at com.firebase.ui.common.BaseObservableSnapshotArray.get(BaseObservableSnapshotArray.java:52)
    at com.firebase.ui.database.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:108)
    at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:148)
    at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
    at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
    at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
    at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
    at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
    at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
    at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:804)
    at android.view.View.layout(View.java:23059)
    at android.view.ViewGroup.layout(ViewGroup.java:6479)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3622)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3082)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2075)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8512)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1076)
    at android.view.Choreographer.doCallbacks(Choreographer.java:897)
    at android.view.Choreographer.doFrame(Choreographer.java:826)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1061)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:236)
    at android.app.ActivityThread.main(ActivityThread.java:8056)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)

below is the code written in my main main.java file below and i have deleted the imports in this question cos that was showing error

package com.example.pahalunitedfoundation;

public class Events extends AppCompatActivity {

  eventAdapter eventAdapter;
  RecyclerView recyclerView;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_events);

    recyclerView = findViewById(R.id.rv);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));


    FirebaseRecyclerOptions<mainModel> options =
            new FirebaseRecyclerOptions.Builder<mainModel>()
                    .setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
                    .build();


    eventAdapter = new eventAdapter(options);
    recyclerView.setAdapter(eventAdapter);
  }

  @Override
  protected void onStart() {
    super.onStart();
    eventAdapter.startListening();
  }

  @Override
  protected void onStop() {
    super.onStop();
    eventAdapter.startListening();
  }
}

below is the code of my adapter class (minus imports)

package com.example.pahalunitedfoundation;


public class eventAdapter extends FirebaseRecyclerAdapter <mainModel,eventAdapter.myViewHolder> {

  /**
   * Initialize a {@link RecyclerView.Adapter} that listens to a Firebase query. See
   * {@link FirebaseRecyclerOptions} for configuration options.
   *
   * @param options
   */
  public eventAdapter(@NonNull FirebaseRecyclerOptions<mainModel> options) {
      super(options);
  }

  @Override
  protected void onBindViewHolder(@NonNull myViewHolder holder, int position, @NonNull mainModel model) {
    holder.ename.setText(model.getEname());
    holder.date.setText(model.getDate());
    holder.description.setText(model.getDescription());
    Glide.with(holder.img.getContext())
      .load(model.getSurl())
      .placeholder(R.drawable.common_google_signin_btn_icon_dark)
      .circleCrop()
      .error(R.drawable.common_google_signin_btn_icon_dark)
      .into(holder.img);
  }

  @NonNull
  @Override
  public myViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.event_item,parent,false);
    return new myViewHolder(view);
  }

  class myViewHolder extends RecyclerView.ViewHolder{
    // enter code here
    CircleImageView img;
    TextView ename,date,description;


    public myViewHolder(@NonNull View itemView) {
        super(itemView);
        img = (CircleImageView)itemView.findViewById(R.id.img1);
        ename = itemView.findViewById(R.id.enametext);
        date = itemView.findViewById(R.id.Date);
        description = itemView.findViewById(R.id.description);
    }
  }
}

CodePudding user response：

A Few issues: the listener probably should be stopped during onStop

@Override
protected void onStop() {
  super.onStop();
  eventAdapter.stopListening(); // was startListening
}

Also the stack trace directly seems to be related to the absence of any real adapter code for the mainModel class. If you could include this class it may help a bit. Right now the recyclerview is setup just try to instantiate a mainModel by passing it whatever is in data I assume it's a string.

FirebaseRecyclerOptions<mainModel> options =
        new FirebaseRecyclerOptions.Builder<mainModel>()
                .setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
                .build();

If the constructor of mainModel doesn't take a String, an adapter would need to be made OR mainModel need to be updated to take a String

CodePudding user response：

Error shows that you have string data in data node of firebase database. So this line of code unable to convert that string to mainModel type.

FirebaseRecyclerOptions<mainModel> options =
            new FirebaseRecyclerOptions.Builder<mainModel>()
                    .setQuery(FirebaseDatabase.getInstance().getReference().child("data"), mainModel.class)
                    .build();

So look out for the database on the firebase console and remove string if you have any inside data node.

Best Practice,

Always give your class a capitalized name.

For example,

Named like this,

public class MainModel

Instead of this,

public class mainModel