使用 firebase 在 android 工作室中搜索

Question

I'm trying to search for that specific entry but I'm getting an error It is important to note that the code of the RecylerView is correct and indeed displays elements only in the search I get an error and I don't know where:

        recyclerView= findViewById(R.id.recycleview);
        getmRootFLY = FirebaseDatabase.getInstance().getReference("FLY");
        list = new ArrayList<>();
        arrayList = new ArrayList<>();
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        myAdapter = new MyAdapter(this,list);
        recyclerView.setAdapter(myAdapter);
        getmRootFLY.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                for (DataSnapshot dataSnapshot: snapshot.getChildren())
                {
                    Fly fly = dataSnapshot.getValue(Fly.class);
                    list.add(fly);
                }
                myAdapter.notifyDataSetChanged();
            }
            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

\\search func.................................

                DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("FLY").child("-NJzbEcGdb8_fvLxWFJk");
                ref.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot)
                    {
                            list.clear();
                            for (DataSnapshot dataSnapshot1: dataSnapshot.getChildren())
                            {
                                Fly fly = dataSnapshot1.getValue(Fly.class);
                                list.add(fly);
                            }
                            myAdapter.notifyDataSetChanged();
                            
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {

                    }
                });
            }
        });
    }
}


//worng in console..............................
 com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.newp.Fly
        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.example.newp.MainActivity$4$1.onDataChange(MainActivity.java:150)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:942)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loopOnce(Looper.java:201)
        at android.os.Looper.loop(Looper.java:288)
        at android.app.ActivityThread.main(ActivityThread.java:7872)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)

Answer 1

You're getting the following error:

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.newp.Fly

Because when you're creating a reference that points to db/FLY/-NJzbEcGdb8_fvLxWFJk and you're looping through the results, you aren't getting Fly objects but strings, hence the error. If you want to get all objects that exist under the FLY node and add them to a list, then you have to remove the call to .child("-NJzbEcGdb8_fvLxWFJk") . So your reference should look like this:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("FLY");
ref.addValueEventListener(/* ... /*);

Edit:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("FLY");
ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot dataSnapshot1: dataSnapshot.getChildren()) {
            String nameFly = dataSnapshot1.child("nameFly").getValue(String.class);
            Log.d(TAG, nameFly);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        Log.d("TAG", error.getMessage()); //Never ignore potential errors!
    }
});