(已弃用) Android Room with a View - Java

compileOptions {
    sourceCompatibility = 1.8
    targetCompatibility = 1.8
}

dependencies {
    implementation "androidx.appcompat:appcompat:$rootProject.appCompatVersion"

    // Dependencies for working with Architecture components
    // You'll probably have to update the version numbers in build.gradle (Project)

    // Room components
    implementation "androidx.room:room-runtime:$rootProject.roomVersion"
    annotationProcessor "androidx.room:room-compiler:$rootProject.roomVersion"
    androidTestImplementation "androidx.room:room-testing:$rootProject.roomVersion"

    // Lifecycle components
    implementation "androidx.lifecycle:lifecycle-viewmodel:$rootProject.lifecycleVersion"
    implementation "androidx.lifecycle:lifecycle-livedata:$rootProject.lifecycleVersion"
    implementation "androidx.lifecycle:lifecycle-common-java8:$rootProject.lifecycleVersion"

    // UI
    implementation "androidx.constraintlayout:constraintlayout:$rootProject.constraintLayoutVersion"
    implementation "com.google.android.material:material:$rootProject.materialVersion"

    // Testing
    testImplementation "junit:junit:$rootProject.junitVersion"
    androidTestImplementation "androidx.arch.core:core-testing:$rootProject.coreTestingVersion"
    androidTestImplementation ("androidx.test.espresso:espresso-core:$rootProject.espressoVersion", {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    androidTestImplementation "androidx.test.ext:junit:$rootProject.androidxJunitVersion"
}

ext {
    appCompatVersion = '1.5.1'
    constraintLayoutVersion = '2.1.4'
    coreTestingVersion = '2.1.0'
    lifecycleVersion = '2.3.1'
    materialVersion = '1.3.0'
    roomVersion = '2.3.0'
    // testing
    junitVersion = '4.13.2'
    espressoVersion = '3.4.0'
    androidxJunitVersion = '1.1.2'
}

public class Word {

   private String mWord;

   public Word(@NonNull String word) {this.mWord = word;}

   public String getWord(){return this.mWord;}
}

@Entity(tableName = "word_table")
public class Word {

   @PrimaryKey
   @NonNull
   @ColumnInfo(name = "word")
   private String mWord;

   public Word(@NonNull String word) {this.mWord = word;}

   public String getWord(){return this.mWord;}
}

@Entity(tableName = "word_table")
public class Word {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @NonNull
    private String word;
    //..other fields, getters, setters
}

@Dao
public interface WordDao {

   // allowing the insert of the same word multiple times by passing a 
   // conflict resolution strategy
   @Insert(onConflict = OnConflictStrategy.IGNORE)
   void insert(Word word);

   @Query("DELETE FROM word_table")
   void deleteAll();

   @Query("SELECT * FROM word_table ORDER BY word ASC")
   List<Word> getAlphabetizedWords();
}

   @Query("SELECT * FROM word_table ORDER BY word ASC")
   LiveData<List<Word>> getAlphabetizedWords();

@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordRoomDatabase extends RoomDatabase {

   public abstract WordDao wordDao();

   private static volatile WordRoomDatabase INSTANCE;
   private static final int NUMBER_OF_THREADS = 4;
   static final ExecutorService databaseWriteExecutor =
        Executors.newFixedThreadPool(NUMBER_OF_THREADS);

   static WordRoomDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (WordRoomDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            WordRoomDatabase.class, "word_database")
                            .build();
                }
            }
        }
        return INSTANCE;
    }
}

class WordRepository {

    private WordDao mWordDao;
    private LiveData<List<Word>> mAllWords;

    // Note that in order to unit test the WordRepository, you have to remove the Application
    // dependency. This adds complexity and much more code, and this sample is not about testing.
    // See the BasicSample in the android-architecture-components repository at
    // https://github.com/googlesamples
    WordRepository(Application application) {
        WordRoomDatabase db = WordRoomDatabase.getDatabase(application);
        mWordDao = db.wordDao();
        mAllWords = mWordDao.getAlphabetizedWords();
    }

    // Room executes all queries on a separate thread.
    // Observed LiveData will notify the observer when the data has changed.
    LiveData<List<Word>> getAllWords() {
        return mAllWords;
    }

    // You must call this on a non-UI thread or your app will throw an exception. Room ensures
    // that you're not doing any long running operations on the main thread, blocking the UI.
    void insert(Word word) {
        WordRoomDatabase.databaseWriteExecutor.execute(() -> {
            mWordDao.insert(word);
        });
    }
}

public class WordViewModel extends AndroidViewModel {

   private WordRepository mRepository;

   private final LiveData<List<Word>> mAllWords;

   public WordViewModel (Application application) {
       super(application);
       mRepository = new WordRepository(application);
       mAllWords = mRepository.getAllWords();
   }

   LiveData<List<Word>> getAllWords() { return mAllWords; }

   public void insert(Word word) { mRepository.insert(word); }
}

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <!-- The default font for RecyclerView items is too small.
    The margin is a simple delimiter between the words. -->
    <style name="word_title">
        <item name="android:layout_width">match_parent</item>
        <item name="android:layout_marginBottom">8dp</item>
        <item name="android:paddingLeft">8dp</item>
        <item name="android:background">@android:color/holo_orange_light</item>
        <item name="android:textAppearance">@android:style/TextAppearance.Large</item>
    </style>
</resources>

<?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="wrap_content">

    <TextView
        android:id="@+id/textView"
        style="@style/word_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/holo_orange_light" />
</LinearLayout>

<androidx.constraintlayout.widget.ConstraintLayout
    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">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="0dp"
        android:layout_height="0dp"
        tools:listitem="@layout/recyclerview_item"
        android:padding="@dimen/big_padding"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:contentDescription="@string/add_word"/>

</androidx.constraintlayout.widget.ConstraintLayout>

<com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:contentDescription="@string/add_word"
        android:src="@drawable/ic_add_black_24dp"/>

class WordViewHolder extends RecyclerView.ViewHolder {
    private final TextView wordItemView;

    private WordViewHolder(View itemView) {
        super(itemView);
        wordItemView = itemView.findViewById(R.id.textView);
    }

    public void bind(String text) {
        wordItemView.setText(text);
    }

    static WordViewHolder create(ViewGroup parent) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recyclerview_item, parent, false);
        return new WordViewHolder(view);
    }
}

public class WordListAdapter extends ListAdapter<Word, WordViewHolder> {

    public WordListAdapter(@NonNull DiffUtil.ItemCallback<Word> diffCallback) {
        super(diffCallback);
    }

    @Override
    public WordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return WordViewHolder.create(parent);
    }

    @Override
    public void onBindViewHolder(WordViewHolder holder, int position) {
        Word current = getItem(position);
        holder.bind(current.getWord());
    }

    static class WordDiff extends DiffUtil.ItemCallback<Word> {

        @Override
        public boolean areItemsTheSame(@NonNull Word oldItem, @NonNull Word newItem) {
            return oldItem == newItem;
        }

        @Override
        public boolean areContentsTheSame(@NonNull Word oldItem, @NonNull Word newItem) {
            return oldItem.getWord().equals(newItem.getWord());
        }
    }
}

RecyclerView recyclerView = findViewById(R.id.recyclerview);
final WordListAdapter adapter = new WordListAdapter(new WordListAdapter.WordDiff());
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

private static RoomDatabase.Callback sRoomDatabaseCallback = new RoomDatabase.Callback() {
    @Override
    public void onCreate(@NonNull SupportSQLiteDatabase db) {
        super.onCreate(db);

        // If you want to keep data through app restarts,
        // comment out the following block
        databaseWriteExecutor.execute(() -> {
            // Populate the database in the background.
            // If you want to start with more words, just add them.
            WordDao dao = INSTANCE.wordDao();
            dao.deleteAll();

            Word word = new Word("Hello");
            dao.insert(word);
            word = new Word("World");
            dao.insert(word);
        });
    }
};

.addCallback(sRoomDatabaseCallback)

<string name="hint_word">Word...</string>
<string name="button_save">Save</string>
<string name="empty_not_saved">Word not saved because it is empty.</string>

<color name="buttonLabel">#FFFFFF</color>

<dimen name="small_padding">8dp</dimen>
<dimen name="big_padding">16dp</dimen>

<activity android:name=".NewWordActivity"></activity>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/edit_word"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:minHeight="@dimen/min_height"
        android:fontFamily="sans-serif-light"
        android:hint="@string/hint_word"
        android:inputType="textAutoComplete"
        android:layout_margin="@dimen/big_padding"
        android:textSize="18sp" />

    <Button
        android:id="@+id/button_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimary"
        android:text="@string/button_save"
        android:layout_margin="@dimen/big_padding"
        android:textColor="@color/buttonLabel" />

</LinearLayout>

public class NewWordActivity extends AppCompatActivity {

   public static final String EXTRA_REPLY = "com.example.android.wordlistsql.REPLY";

   private  EditText mEditWordView;

   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_new_word);
       mEditWordView = findViewById(R.id.edit_word);

       final Button button = findViewById(R.id.button_save);
       button.setOnClickListener(view -> {
           Intent replyIntent = new Intent();
           if (TextUtils.isEmpty(mEditWordView.getText())) {
               setResult(RESULT_CANCELED, replyIntent);
           } else {
               String word = mEditWordView.getText().toString();
               replyIntent.putExtra(EXTRA_REPLY, word);
               setResult(RESULT_OK, replyIntent);
           }
           finish();
       });
   }
}

private WordViewModel mWordViewModel;

mWordViewModel = new ViewModelProvider(this).get(WordViewModel.class);

mWordViewModel.getAllWords().observe(this, words -> {
    // Update the cached copy of the words in the adapter.
    adapter.submitList(words);
});

public static final int NEW_WORD_ACTIVITY_REQUEST_CODE = 1;

public void onActivityResult(int requestCode, int resultCode, Intent data) {
   super.onActivityResult(requestCode, resultCode, data);

   if (requestCode == NEW_WORD_ACTIVITY_REQUEST_CODE && resultCode == RESULT_OK) {
       Word word = new Word(data.getStringExtra(NewWordActivity.EXTRA_REPLY));
       mWordViewModel.insert(word);
   } else {
       Toast.makeText(
               getApplicationContext(),
               R.string.empty_not_saved,
               Toast.LENGTH_LONG).show();
   }
}

FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener( view -> {
   Intent intent = new Intent(MainActivity.this, NewWordActivity.class);
   startActivityForResult(intent, NEW_WORD_ACTIVITY_REQUEST_CODE);
});