Items not showing up in RecycleView from Room database

问题

After previous debugging I've asserted that my database is indeed working correctly however even though it appears although I've set up the ReycleViewAdapter correctly the data is not displaying.

I connect to my database in my main activity and pass the information to my fragment using an interface. This List<GlobalLists> data is then passed as a parameter to my Adapter for use in the onBind method; previously I was presenting this data in a list view but when I wanted live updates I had to switch to a recycle view. Can someone point out what's happening here?

The DataCommunication.java object is the interface which I've omitted because it just contains the methods for data retrieval,

My XML:

show_all_lists.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <android.support.v7.widget.RecyclerView
        android:id="@+id/allItems"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </android.support.v7.widget.RecyclerView>

</LinearLayout>

custom_row.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/customRow"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">

    <ImageView
        android:id="@+id/rowImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_info_outline"/>

    <TextView
        android:id="@+id/rowTitle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

RecycleViewAdapter.java

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;    
import java.util.List;

public class RecycleViewAdapter extends RecyclerView.Adapter<RecycleViewAdapter.ViewHolder> {

    private LayoutInflater inflater = null;
    private List<GlobalLists> results = null;

    public RecycleViewAdapter(Context context, List<GlobalLists> results){
        this.inflater = LayoutInflater.from(context);
        this.results = results;
    }    
    @NonNull
    @Override
    public RecycleViewAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.custom_row, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull RecycleViewAdapter.ViewHolder holder, int position, @NonNull List<Object> payloads) {
        super.onBindViewHolder(holder, position, payloads);
        GlobalLists item = this.results.get(position);
        holder.rowTitle.setText(item.getTitle());


    }    
    @Override
    public int getItemCount() {
        return 0;
    }

    @Override
    public void onBindViewHolder(@NonNull RecycleViewAdapter.ViewHolder holder, int position) {

    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        private TextView rowTitle = null;
        private ImageView rowImage = null;

        public ViewHolder(View itemView) {
            super(itemView);
            this.rowTitle = itemView.findViewById(R.id.rowTitle);
            this.rowImage = itemView.findViewById(R.id.rowImage);

        }
    }
}

ShowAllListsFragment.java

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;
import java.util.Observable;
import java.util.Observer;


public class showAllLists_fragment extends android.support.v4.app.Fragment implements Observer{

    private static final String TAG = "showAllLists";           
    private RecyclerView mAllItemsView = null;
    private RecycleViewAdapter mRecycleAdapter = null;
    private DataCommunication mData = null;
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        super.onCreateView(inflater,container,savedInstanceState);
        View view = inflater.inflate(R.layout.show_all_lists_frag, container, false);


        this.mAllItemsView = (RecyclerView) view.findViewById(R.id.allItems);
        this.mRecycleAdapter = new RecycleViewAdapter(getActivity(), this.mData.getResults());
        this.mAllItemsView.setAdapter(this.mRecycleAdapter);
        this.mAllItemsView.setLayoutManager(new LinearLayoutManager(getActivity()));




        return view;
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        try {
            this.mData = (DataCommunication) context;
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString()
                    + " must implement DataCommunication");
        }
    }    
    @Override
    public void onPause() {
        super.onPause();
        Log.d(TAG, "Paused!");
    }   

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void update(Observable o, Object arg) {
        View root = getView();
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements DataCommunication{

    private static final String TAG = "MainActivity";
    private SectionsPageAdapter mSectionsPageAdapter = null;
    private ViewPager pager = null;
    private  BloomDatabase userData = null;    
    private String selectedTitle = null;
    private String selectedContent = null;
    private List<GlobalLists> searchResults = null;    


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate: Starting...");
        this.userData = BloomDatabase.getFileDatabase(this);
        this.searchResults = this.userData.listModel().loadAllLists();


        mSectionsPageAdapter = new SectionsPageAdapter(getSupportFragmentManager());

        pager = (ViewPager) findViewById(R.id.container);
        setupViewPager(pager);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(pager);


    }


    private void setupViewPager(ViewPager pager){

        SectionsPageAdapter adapter = new SectionsPageAdapter(getSupportFragmentManager());
        adapter.addFragment(new itemView_fragment(), "Detail View");
        adapter.addFragment(new showAllLists_fragment(), "All Lists");
        adapter.addFragment(new addList_fragment(), "Add List");
        pager.setAdapter(adapter);
    }


    @Override
    public String getItemTitle(){
        return this.selectedTitle;
    }

    @Override
    public String getItemContents() {
        return this.selectedContent;
    }

    @Override
    public void setItemTitle(String title) {
        this.selectedTitle = title;
    }

    @Override
    public void setItemContent(String content) {
        this.selectedContent = content;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main,menu);

        final MenuItem searchItem = menu.findItem(R.id.action_search);
        final SearchView searchDatabase = (SearchView) searchItem.getActionView();

        searchDatabase.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String query) {
                return searchTerm(query);
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                return false;
            }
        });

        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean searchTerm(String title) {
        try {
            this.searchResults = this.userData.listModel().searchByTitle(title);
            Log.d(TAG, "Search Successful!");
            return true;
        } catch (Exception e){
            Log.d(TAG, "Search Failed \n -See Console");
            return false;
        }
    }

    @Override
    public List<GlobalLists> getResults() {
        return this.searchResults;
    }

    @Override
    public void refresh(){
        this.mSectionsPageAdapter.updateFragments();
    }

}

回答1:

There are two mistake in your adapter class correct

1). You should return the size of your data results ArrayList in getItemCount()

Use this

@Override
public int getItemCount() {
      return results.size();
}

Instead of this

@Override
public int getItemCount() {
    return 0;
}

2) Change your custom_row.xml hight to wrap_content like below code

Use this

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/customRow"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

Instead of this

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/customRow"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">

来源：https://stackoverflow.com/questions/49109641/items-not-showing-up-in-recycleview-from-room-database

标签

java

android

android-layout

android-recyclerview