Part 6 – RecyclerView + Adapter


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In part 6 of the Architecture Components tutorial, we will set up a RecyclerView to display the entries from our database table in our activity.
For this we first prepare the XML layout for the single CardView rows and then create a RecyclerView.Adapter, where we add a ViewHolder as an inner class and implement onCreateViewHolder, onBindViewHolder and getItemCount to inflate it and populate it with data.
To update the ArrayList in the onChanged callback of our LiveData, we add another public method to the adapter where we pass the new List and call notifyDataSetChanged.

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Links & Dependenciesnote_item.xmlactivity_main.xmlNoteAdapter.javaNoteViewModel.javaMainActivity.javaNoteRepository.javaNoteDao.javaNoteDatabase.javaNote.java

“Adding Components” page with dependencies & instructions:

developer.android.com/topic/libraries/architecture/adding-components

 

CardView & Design Support Library:

developer.android.com/topic/libraries/support-library/packages#v7-cardview

developer.android.com/topic/libraries/support-library/packages#design

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp">

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="8dp">

        <TextView
            android:id="@+id/text_view_priority"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentEnd="true"
            android:text="1"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />

        <TextView
            android:id="@+id/text_view_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_toStartOf="@id/text_view_priority"
            android:ellipsize="end"
            android:maxLines="1"
            android:text="Title"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />

        <TextView
            android:id="@+id/text_view_description"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/text_view_title"
            android:text="Description" />

    </RelativeLayout>

</android.support.v7.widget.CardView>
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:listitem="@layout/note_item" />

</android.support.design.widget.CoordinatorLayout>
package com.codinginflow.architectureexample;

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.TextView;

import java.util.ArrayList;
import java.util.List;

public class NoteAdapter extends RecyclerView.Adapter<NoteAdapter.NoteHolder> {
    private List<Note> notes = new ArrayList<>();

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

    @Override
    public void onBindViewHolder(@NonNull NoteHolder holder, int position) {
        Note currentNote = notes.get(position);
        holder.textViewTitle.setText(currentNote.getTitle());
        holder.textViewDescription.setText(currentNote.getDescription());
        holder.textViewPriority.setText(String.valueOf(currentNote.getPriority()));
    }

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

    public void setNotes(List<Note> notes) {
        this.notes = notes;
        notifyDataSetChanged();
    }

    class NoteHolder extends RecyclerView.ViewHolder {
        private TextView textViewTitle;
        private TextView textViewDescription;
        private TextView textViewPriority;

        public NoteHolder(View itemView) {
            super(itemView);
            textViewTitle = itemView.findViewById(R.id.text_view_title);
            textViewDescription = itemView.findViewById(R.id.text_view_description);
            textViewPriority = itemView.findViewById(R.id.text_view_priority);
        }
    }
}
package com.codinginflow.architectureexample;

import android.app.Application;
import android.arch.lifecycle.AndroidViewModel;
import android.arch.lifecycle.LiveData;
import android.support.annotation.NonNull;

import java.util.List;

public class NoteViewModel extends AndroidViewModel {
    private NoteRepository repository;
    private LiveData<List<Note>> allNotes;

    public NoteViewModel(@NonNull Application application) {
        super(application);
        repository = new NoteRepository(application);
        allNotes = repository.getAllNotes();
    }

    public void insert(Note note) {
        repository.insert(note);
    }

    public void update(Note note) {
        repository.update(note);
    }

    public void delete(Note note) {
        repository.delete(note);
    }

    public void deleteAllNotes() {
        repository.deleteAllNotes();
    }

    public LiveData<List<Note>> getAllNotes() {
        return allNotes;
    }
}
package com.codinginflow.architectureexample;

import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

import java.util.List;

public class MainActivity extends AppCompatActivity {
    private NoteViewModel noteViewModel;

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

        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        final NoteAdapter adapter = new NoteAdapter();
        recyclerView.setAdapter(adapter);

        noteViewModel = ViewModelProviders.of(this).get(NoteViewModel.class);
        noteViewModel.getAllNotes().observe(this, new Observer<List<Note>>() {
            @Override
            public void onChanged(@Nullable List<Note> notes) {
                adapter.setNotes(notes);
            }
        });
    }
}
package com.codinginflow.architectureexample;

import android.app.Application;
import android.arch.lifecycle.LiveData;
import android.os.AsyncTask;

import java.util.List;

public class NoteRepository {
    private NoteDao noteDao;
    private LiveData<List<Note>> allNotes;

    public NoteRepository(Application application) {
        NoteDatabase database = NoteDatabase.getInstance(application);
        noteDao = database.noteDao();
        allNotes = noteDao.getAllNotes();
    }

    public void insert(Note note) {
        new InsertNoteAsyncTask(noteDao).execute(note);
    }

    public void update(Note note) {
        new UpdateNoteAsyncTask(noteDao).execute(note);
    }

    public void delete(Note note) {
        new DeleteNoteAsyncTask(noteDao).execute(note);
    }

    public void deleteAllNotes() {
        new DeleteAllNotesAsyncTask(noteDao).execute();
    }

    public LiveData<List<Note>> getAllNotes() {
        return allNotes;
    }

    private static class InsertNoteAsyncTask extends AsyncTask<Note, Void, Void> {
        private NoteDao noteDao;

        private InsertNoteAsyncTask(NoteDao noteDao) {
            this.noteDao = noteDao;
        }

        @Override
        protected Void doInBackground(Note... notes) {
            noteDao.insert(notes[0]);
            return null;
        }
    }

    private static class UpdateNoteAsyncTask extends AsyncTask<Note, Void, Void> {
        private NoteDao noteDao;

        private UpdateNoteAsyncTask(NoteDao noteDao) {
            this.noteDao = noteDao;
        }

        @Override
        protected Void doInBackground(Note... notes) {
            noteDao.update(notes[0]);
            return null;
        }
    }

    private static class DeleteNoteAsyncTask extends AsyncTask<Note, Void, Void> {
        private NoteDao noteDao;

        private DeleteNoteAsyncTask(NoteDao noteDao) {
            this.noteDao = noteDao;
        }

        @Override
        protected Void doInBackground(Note... notes) {
            noteDao.delete(notes[0]);
            return null;
        }
    }

    private static class DeleteAllNotesAsyncTask extends AsyncTask<Void, Void, Void> {
        private NoteDao noteDao;

        private DeleteAllNotesAsyncTask(NoteDao noteDao) {
            this.noteDao = noteDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            noteDao.deleteAllNotes();
            return null;
        }
    }
}
package com.codinginflow.architectureexample;

import android.arch.lifecycle.LiveData;
import android.arch.persistence.room.Dao;
import android.arch.persistence.room.Delete;
import android.arch.persistence.room.Insert;
import android.arch.persistence.room.Query;
import android.arch.persistence.room.Update;

import java.util.List;

@Dao
public interface NoteDao {

    @Insert
    void insert(Note note);

    @Update
    void update(Note note);

    @Delete
    void delete(Note note);

    @Query("DELETE FROM note_table")
    void deleteAllNotes();

    @Query("SELECT * FROM note_table ORDER BY priority DESC")
    LiveData<List<Note>> getAllNotes();
}
package com.codinginflow.architectureexample;

import android.arch.persistence.db.SupportSQLiteDatabase;
import android.arch.persistence.room.Database;
import android.arch.persistence.room.Room;
import android.arch.persistence.room.RoomDatabase;
import android.content.Context;
import android.os.AsyncTask;
import android.support.annotation.NonNull;

@Database(entities = {Note.class}, version = 1)
public abstract class NoteDatabase extends RoomDatabase {

    private static NoteDatabase instance;

    public abstract NoteDao noteDao();

    public static synchronized NoteDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    NoteDatabase.class, "note_database")
                    .fallbackToDestructiveMigration()
                    .addCallback(roomCallback)
                    .build();
        }
        return instance;
    }

    private static RoomDatabase.Callback roomCallback = new RoomDatabase.Callback() {
        @Override
        public void onCreate(@NonNull SupportSQLiteDatabase db) {
            super.onCreate(db);
            new PopulateDbAsyncTask(instance).execute();
        }
    };

    private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, Void> {
        private NoteDao noteDao;

        private PopulateDbAsyncTask(NoteDatabase db) {
            noteDao = db.noteDao();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            noteDao.insert(new Note("Title 1", "Description 1", 1));
            noteDao.insert(new Note("Title 2", "Description 2", 2));
            noteDao.insert(new Note("Title 3", "Description 3", 3));
            return null;
        }
    }
}
package com.codinginflow.architectureexample;

import android.arch.persistence.room.Entity;
import android.arch.persistence.room.PrimaryKey;

@Entity(tableName = "note_table")
public class Note {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String title;

    private String description;

    private int priority;

    public Note(String title, String description, int priority) {
        this.title = title;
        this.description = description;
        this.priority = priority;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public int getPriority() {
        return priority;
    }
}