从Firebase数据库检索对象到我的RecyclerView中

Question

I have tried some the suggestions from similar questions on here as you can see in some commented out code. I am new at all of this so could you please help me out? Let me know if you need anymore to code to try to solve the problem. Thank you in advance.

I even tried to doing what the error says but I really dont know where to put the GenericTypeIndicator.

I am getting this error:

com.google.firebase.database.DatabaseException: Class java.util.List has generic type parameters, please use GenericTypeIndicator instead at com.google.android.gms.internal.zzelw.zzb(Unknown Source) at com.google.android.gms.internal.zzelw.zza(Unknown Source) at com.google.android.gms.internal.zzelw.zzb(Unknown Source) at com.google.android.gms.internal.zzelx.zze(Unknown Source) at com.google.android.gms.internal.zzelw.zzb(Unknown Source) at com.google.android.gms.internal.zzelw.zza(Unknown Source) at com.google.firebase.database.DataSnapshot.getValue(Unknown Source) at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:29) ...

Here is my code:

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.homeRecyclerView)
    RecyclerView mHomeRecyclerView;

    @BindView(R.id.emptyTextView)
    TextView mEmptyTextView;

    protected static final Query sInspirationQuery =
            FirebaseDatabase.getInstance().getReference().child("Inspirations");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);


        ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayShowTitleEnabled(false);
        actionBar.setDisplayShowHomeEnabled(true);
        actionBar.setIcon(R.mipmap.ic_launcher);

        //mHomeRecyclerView.setHasFixedSize(true);
        mHomeRecyclerView.setLayoutManager(new LinearLayoutManager(this));


    }

    @Override
    protected void onStart() {
        super.onStart();


        attachRvAdapter();
    }

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.options_menu, menu);
        Drawable addInspirationDrawable = menu.findItem(R.id.addInspiration).getIcon();
        Drawable userAccountDrawable = menu.findItem(R.id.userAccount).getIcon();
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if(id == R.id.addInspiration) {
            String className = "com.example.jessie.inspirationexchange.CreateActivity";
            nextActivity(className);
        } else if(id == R.id.userAccount) {
            String className = "com.example.jessie.inspirationexchange.UserActivity";
            nextActivity(className);
        }
        return super.onOptionsItemSelected(item);
    }

    private void nextActivity(String className) {
        Intent intent = null;
        try {
            intent = new Intent(this, Class.forName(className));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        startActivity(intent);
    }

    public void attachRvAdapter() {
        RecyclerView.Adapter adapter = newAdapter();
        mHomeRecyclerView.setAdapter(adapter);
    }



    protected RecyclerView.Adapter newAdapter() {
        FirebaseRecyclerOptions<Inspiration> options =
                new FirebaseRecyclerOptions.Builder<Inspiration>()
                        .setQuery(sInspirationQuery, Inspiration.class)
                        .setLifecycleOwner(this)
                        .build();

        return new FirebaseRecyclerAdapter<Inspiration, CardViewHolder>(options) {
            @Override
            public CardViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                return new CardViewHolder(LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.inspiration_card, parent, false));
            }

            @Override
            protected void onBindViewHolder(@NonNull CardViewHolder holder, int position, @NonNull Inspiration model) {
                holder.bind(model);
            }

//            SnapshotParser<Inspiration> mSnapshotParser = new SnapshotParser<Inspiration>() {
//                @NonNull
//                @Override
//                public Inspiration parseSnapshot(@NonNull DataSnapshot snapshot) {
//                    GenericTypeIndicator<List<Inspiration>> t = new GenericTypeIndicator<List<Inspiration>>();
//
//                    return (Inspiration) snapshot.child("Inspirations").getValue(t);
//                }
//            };

            @Override
            public void onDataChanged() {
                super.onDataChanged();

                //GenericTypeIndicator<List<Inspiration>> t = new GenericTypeIndicator<List<Inspiration>>();
                mEmptyTextView.setVisibility(getItemCount() == 0 ? View.VISIBLE : View.GONE);
            }


        };

    }

}

My model:

public class Inspiration {

    private String mTitle;
    private String mBody;
    private List<String> mCategoriesChose;
    private String mAuthor;

    public Inspiration() {
    }

    public Inspiration(String title, String body, List categories) {
        mTitle = title;
        mBody = body;
        mCategoriesChose = categories;
    }

    public String getAuthor() {
        return mAuthor;
    }

    public void setAuthor(String author) {
        mAuthor = author;
    }

    public String getTitle() {
        return mTitle;
    }

    public void setTitle(String title) {
        mTitle = title;
    }

    public String getBody() {
        return mBody;
    }

    public void setBody(String body) {
        mBody = body;
    }

    public List<String> getCategoriesChose() {
        return mCategoriesChose;
    }

    public void setCategoriesChose(List categoriesChose) {
        mCategoriesChose = categoriesChose;
    }

    @Override
    public String toString() {
        return "Inspiration{" +
                "mTitle='" + mTitle + '\'' +
                ", mBody='" + mBody + '\'' +
                ", mCategoriesChose=" + mCategoriesChose.toString() +
                '}';
    }

}

Here is what the JSON looks like(just 1 object)

{
  "Inspirations" : {
    "-L5un07HfHu0XT-XfLX2" : {
      "author" : "User1",
      "body" : "test 1",
      "categoriesChose" : [ "Character", "Courage", "Determination" ],
      "title" : "gov"
    }
  }
}

Answer 1

You can't have List and Map type objects within the main object that you're trying to deserialize. It's because of the way the Java type erasure system works. At runtime, it's impossible to know via reflection what generic types your List or Map declares, which means it doesn't know what type of objects are safe to put in there.

GenericTypeIndicator works with getValue() when the top-level object you're trying to deserialize is a generic List, but that's about it. It doesn't work if it's embedded anywhere inside. The error message is a bit misleading on that point. You'll have to pull items out of the snapshot and create objects out of them yourself.

Answer 2

I solved this problem by removing the nested array that I had inside of my database. After removing this it worked like a charm. If someone wants to answer how resolve that the nested array inside database problem, feel free to post.