Part 10 – ListAdapter – Coding in Flow

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In part 10 of the Architecture Components tutorial, we will refactor our RecyclerView.Adapter to a ListAdapter, which has been added in the support library version 27.1.0. The ListAdapter is a subclass of the normal RecyclerView adapter, that implements AsyncListDiffer to calculate the differences between the old data set and the new one we get passed in the LiveData’s onChanged method, so we don’t have to rely on notifyDataSetChanged to update our adapter.
AsyncListDiffer runs DiffUtil on a background thread to calculate the differences between two lists and dispatches the result to the RecyclerView adapter on the main thread. The adapter then internally uses one of the more granular notify methods, like notifyItemRangeInserted, notifyItemRangeRemoved or notifyItemRangeChanged, which also give us the default RecyclerView insert, remove and update animations. We just have to make some small changes in our adapter, like using getItem and submitList instead of our old methods, and provide a DiffUtil.ItemCallBack, where we define the list comparison logic in areItemsTheSame and areContentsTheSame. Both methods pass us the oldItem and the newItem, which we can then compare for positional and content changes.

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Links & Dependenciesmain_menu.xmlactivity_add_note.xmladd_note_menu.xmlAddEditNoteActivity.javaAndroidManifest.xmlnote_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"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/delete_all_notes"
        android:title="Delete all notes"
        app:showAsAction="never" />
</menu>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context=".AddEditNoteActivity">

    <EditText
        android:id="@+id/edit_text_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Title"
        android:inputType="text" />

    <EditText
        android:id="@+id/edit_text_description"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Description"
        android:inputType="textMultiLine" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="Priority:"
        android:textAppearance="@android:style/TextAppearance.Medium" />

    <NumberPicker
        android:id="@+id/number_picker_priority"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/save_note"
        android:icon="@drawable/ic_save"
        android:title="Save"
        app:showAsAction="ifRoom" />
</menu>

package com.codinginflow.architectureexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.NumberPicker;
import android.widget.Toast;

public class AddEditNoteActivity extends AppCompatActivity {
    public static final String EXTRA_ID =
            "com.codinginflow.architectureexample.EXTRA_ID";
    public static final String EXTRA_TITLE =
            "com.codinginflow.architectureexample.EXTRA_TITLE";
    public static final String EXTRA_DESCRIPTION =
            "com.codinginflow.architectureexample.EXTRA_DESCRIPTION";
    public static final String EXTRA_PRIORITY =
            "com.codinginflow.architectureexample.EXTRA_PRIORITY";

    private EditText editTextTitle;
    private EditText editTextDescription;
    private NumberPicker numberPickerPriority;

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

        editTextTitle = findViewById(R.id.edit_text_title);
        editTextDescription = findViewById(R.id.edit_text_description);
        numberPickerPriority = findViewById(R.id.number_picker_priority);

        numberPickerPriority.setMinValue(1);
        numberPickerPriority.setMaxValue(10);

        getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_close);

        Intent intent = getIntent();

        if (intent.hasExtra(EXTRA_ID)) {
            setTitle("Edit Note");
            editTextTitle.setText(intent.getStringExtra(EXTRA_TITLE));
            editTextDescription.setText(intent.getStringExtra(EXTRA_DESCRIPTION));
            numberPickerPriority.setValue(intent.getIntExtra(EXTRA_PRIORITY, 1));
        } else {
            setTitle("Add Note");
        }
    }

    private void saveNote() {
        String title = editTextTitle.getText().toString();
        String description = editTextDescription.getText().toString();
        int priority = numberPickerPriority.getValue();

        if (title.trim().isEmpty() || description.trim().isEmpty()) {
            Toast.makeText(this, "Please insert a title and description", Toast.LENGTH_SHORT).show();
            return;
        }

        Intent data = new Intent();
        data.putExtra(EXTRA_TITLE, title);
        data.putExtra(EXTRA_DESCRIPTION, description);
        data.putExtra(EXTRA_PRIORITY, priority);

        int id = getIntent().getIntExtra(EXTRA_ID, -1);
        if (id != -1) {
            data.putExtra(EXTRA_ID, id);
        }

        setResult(RESULT_OK, data);
        finish();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.add_note_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.save_note:
                saveNote();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.architectureexample">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".AddEditNoteActivity"
            android:parentActivityName=".MainActivity" />
    </application>

</manifest>

<?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.FloatingActionButton
        android:id="@+id/button_add_note"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="32dp"
        android:src="@drawable/ic_add" />

</android.support.design.widget.CoordinatorLayout>

package com.codinginflow.architectureexample;

import android.support.annotation.NonNull;
import android.support.v7.recyclerview.extensions.ListAdapter;
import android.support.v7.util.DiffUtil;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class NoteAdapter extends ListAdapter<Note, NoteAdapter.NoteHolder> {
    private OnItemClickListener listener;

    public NoteAdapter() {
        super(DIFF_CALLBACK);
    }

    private static final DiffUtil.ItemCallback<Note> DIFF_CALLBACK = new DiffUtil.ItemCallback<Note>() {
        @Override
        public boolean areItemsTheSame(Note oldItem, Note newItem) {
            return oldItem.getId() == newItem.getId();
        }

        @Override
        public boolean areContentsTheSame(Note oldItem, Note newItem) {
            return oldItem.getTitle().equals(newItem.getTitle()) &&
                    oldItem.getDescription().equals(newItem.getDescription()) &&
                    oldItem.getPriority() == newItem.getPriority();
        }
    };

    @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 = getItem(position);
        holder.textViewTitle.setText(currentNote.getTitle());
        holder.textViewDescription.setText(currentNote.getDescription());
        holder.textViewPriority.setText(String.valueOf(currentNote.getPriority()));
    }

    public Note getNoteAt(int position) {
        return getItem(position);
    }

    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);

            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int position = getAdapterPosition();
                    if (listener != null && position != RecyclerView.NO_POSITION) {
                        listener.onItemClick(getItem(position));
                    }
                }
            });
        }
    }

    public interface OnItemClickListener {
        void onItemClick(Note note);
    }

    public void setOnItemClickListener(OnItemClickListener listener) {
        this.listener = listener;
    }
}

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.content.Intent;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

import java.util.List;

public class MainActivity extends AppCompatActivity {
    public static final int ADD_NOTE_REQUEST = 1;
    public static final int EDIT_NOTE_REQUEST = 2;

    private NoteViewModel noteViewModel;

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

        FloatingActionButton buttonAddNote = findViewById(R.id.button_add_note);
        buttonAddNote.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, AddEditNoteActivity.class);
                startActivityForResult(intent, ADD_NOTE_REQUEST);
            }
        });

        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.submitList(notes);
            }
        });

        new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,
                ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
            @Override
            public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
                return false;
            }

            @Override
            public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
                noteViewModel.delete(adapter.getNoteAt(viewHolder.getAdapterPosition()));
                Toast.makeText(MainActivity.this, "Note deleted", Toast.LENGTH_SHORT).show();
            }
        }).attachToRecyclerView(recyclerView);

        adapter.setOnItemClickListener(new NoteAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(Note note) {
                Intent intent = new Intent(MainActivity.this, AddEditNoteActivity.class);
                intent.putExtra(AddEditNoteActivity.EXTRA_ID, note.getId());
                intent.putExtra(AddEditNoteActivity.EXTRA_TITLE, note.getTitle());
                intent.putExtra(AddEditNoteActivity.EXTRA_DESCRIPTION, note.getDescription());
                intent.putExtra(AddEditNoteActivity.EXTRA_PRIORITY, note.getPriority());
                startActivityForResult(intent, EDIT_NOTE_REQUEST);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == ADD_NOTE_REQUEST && resultCode == RESULT_OK) {
            String title = data.getStringExtra(AddEditNoteActivity.EXTRA_TITLE);
            String description = data.getStringExtra(AddEditNoteActivity.EXTRA_DESCRIPTION);
            int priority = data.getIntExtra(AddEditNoteActivity.EXTRA_PRIORITY, 1);

            Note note = new Note(title, description, priority);
            noteViewModel.insert(note);

            Toast.makeText(this, "Note saved", Toast.LENGTH_SHORT).show();
        } else if (requestCode == EDIT_NOTE_REQUEST && resultCode == RESULT_OK) {
            int id = data.getIntExtra(AddEditNoteActivity.EXTRA_ID, -1);

            if (id == -1) {
                Toast.makeText(this, "Note can't be updated", Toast.LENGTH_SHORT).show();
                return;
            }

            String title = data.getStringExtra(AddEditNoteActivity.EXTRA_TITLE);
            String description = data.getStringExtra(AddEditNoteActivity.EXTRA_DESCRIPTION);
            int priority = data.getIntExtra(AddEditNoteActivity.EXTRA_PRIORITY, 1);

            Note note = new Note(title, description, priority);
            note.setId(id);
            noteViewModel.update(note);

            Toast.makeText(this, "Note updated", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Note not saved", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.main_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.delete_all_notes:
                noteViewModel.deleteAllNotes();
                Toast.makeText(this, "All notes deleted", Toast.LENGTH_SHORT).show();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}

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;
    }
}