Data retrieve on Data Change in firebase getting Error

Question

I am making an android app based on firebase. My logcat showing error on data change. Here is the code:

myRef.child("first").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
                    model model = childSnapshot.getValue(model.class);
                    if (dataSnapshot.getValue() == null) {
                       Toast.makeText(getApplicationContext(),"Sorry",Toast.LENGTH_SHORT).show();
                    } else {

                        String name = model.getFb01name();
                        

                        tvName.setText(name);
                        

                    }

                }
            }

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

            }


        });

Can anybody improve it?

Here is my logcat error message: It is showing error on this line.

 model model = childSnapshot.getValue(model.class);

"at my_project_name.SheetActivity$3.onDataChange(SheetActivity.java:156)"

2020-11-23 17:41:35.403 5585-5585/my_project_name E/AndroidRuntime: FATAL EXCEPTION: main
    Process: my_project_name, PID: 5585
    com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.Long to type my_project_name.Model.model
        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 my_project_name.SheetActivity$3.onDataChange(SheetActivity.java:156)
        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$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

I have tried a lot. Sometimes it worked but stopped again. I cannot point out where is the mistake.

my model class goes as follow:

public class model {
    private String fb01name;
   


    public model() {
    }

    public model(String fb01name) {
        this.fb01name = fb01name;
        
    }

    public String getFb01name() {
        return fb01name;
    }

    public void setFb01name(String fb01name) {
        this.fb01name = fb01name;
    }

}

My firebase structure is like this:

This the latest logcat message after applying the suggestion:

2020-11-24 00:40:06.783 12399-12399/my_project_nameE/AndroidRuntime: FATAL EXCEPTION: main
    Process: my_project_name, PID: 12399
    com.google.firebase.database.DatabaseException: Failed to convert value of type java.lang.Long to String
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertString(CustomClassMapper.java:426)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:217)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(CustomClassMapper.java:179)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(CustomClassMapper.java:48)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:593)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:563)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:433)
        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 my_project_name.SheetActivity$3.onDataChange(SheetActivity.java:155)
        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$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Answer 1

Here try this, if your model class has only one parameter this should be fine. If you need all the parameters that are in your database, you will need to extract all from database and then add it to your model.

myRef.child("first").addValueEventListener(new ValueEventListener() {

    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
      String name = (String) dataSnapshot.child("fb01name").getValue().toString;
        if(name == null){
        
            Toast.makeText(getApplicationContext(),"Sorry",Toast.LENGTH_SHORT).show();
            return;
        
        }
    
        model model = new model(name);
        tvName.setText(name);
    
    
    }
    
    @Override
    public void onCancelled(@NonNull DatabaseError error) {
    
    }

});

Answer 2

Since you read from first, the DataSnapshot that you get in onDataChange contains the data at that location. You then loop over the children in the snapshot, so your childSnapshot variable then points to the individual properties under first (so fb00max, fb01mark1, etc). And when you then try to read a model object from that single value, it fails as the value 10 can't be interpreted as a model.

You'll either have to read from one level higher in the tree, or remove the loop from your onDataChange.

read from one level higher in the tree

myRef.addValueEventListener(new ValueEventListener() {
    ...

remove the loop from your onDataChange

myRef.child("first").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        model model = dataSnapshot.getValue(model.class);
        if (dataSnapshot.getValue() == null) {
           Toast.makeText(getApplicationContext(),"Sorry",Toast.LENGTH_SHORT).show();
        } else {
            String name = model.getFb01name();
            
            tvName.setText(name);                    
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException(); // Never ignore errors
    }
});