Better Data Persistence on Android

Better Data Persistence on Android
Eric Maxwell

Credible Software

What to Expect
• Android Storage Options
• Focus on SQLite / Database Storage
• Make it better using the Realm Mobile Database

Android Storage Options
• Shared Preferences

• Disk Storage
• Internal
• External

• Disk Storage
• Internal
• External
• Relational Database w/ SQLite

SQLite
• Relational Database on the device
• android.database.sqlite.SQLiteDatabase
• Perform insert, query, update, delete, begin/end
transaction
• android.database.sqlite.SQLiteOpenHelper
• Handle Create, Upgrade events

Nae Nae Assistant App
• List of Nae Nae Lyrics
• Add New
• Delete
• Persistent across launches

View Layout
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:orientation="vertical" > 
 
<GridLayout 
android:id="@+id/lyricButtons" 
android:layout_height="wrap_content" 
android:padding="10dp"> 
 
<Button 
android:id="@+id/watch_me" 
android:text="@string/lyric_watch_me" 
android:onClick="add"/> 
 
<Button 
android:id="@+id/whip" 
android:text="@string/lyric_whip" 
 
<Button 
android:id="@+id/nea" 
android:text="@string/lyric_nea" 
 
<Button 
android:id="@+id/bop" 
android:text="@string/lyric_bop" 
 
</GridLayout> 
 
<ListView 
android:id="@android:id/list" 
android:layout_height="wrap_content" 
android:text="@string/hello_world" /> 
 
</LinearLayout>

Simple Data Object
public class Lyric {
 
private long id; 
private String lyricText; 
 
// Getters / Setters... 
 
// Will be used by the ArrayAdapter in the ListView 
@Override 
public String toString() { 
return lyricText; 
} 
}

Activity - Lifecycle Events
public class NaeNaeActivity extends ListActivity { 
 
private LyricDataSource datasource; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_naenae); 
 
datasource = new LyricDataSource(this); 
datasource.open(); 
 
List<Lyric> values = datasource.getAllLyrics(); 
 
// Use the SimpleCursorAdapter to show the 
// elements in a ListView 
ArrayAdapter<Lyric> adapter = new ArrayAdapter<Lyric>(this, 
android.R.layout.simple_list_item_1, values); 
setListAdapter(adapter);
 
} 
 
@Override 
protected void onResume() { 
super.onResume(); 
datasource.open(); 
} 
 
@Override 
protected void onPause() { 
super.onPause(); 
datasource.close(); 
}
...
}
The datasource gets
initialized and opened on
create and is then used to
get all of the lyrics and
placed into an array
adapter.
The datasource is opened
and closed on resume and
stop.

Activity - Events Add/Remove
public void add(View view) { 
String lyricText = ((Button) view).getText().toString(); 
if (!TextUtils.isEmpty(lyricText)) { 
ArrayAdapter<Lyric> adapter = getListAdapter(); 
Lyric lyric = null; 
lyric = datasource.createLyric(lyricText); 
adapter.add(lyric); 
} 
} 
 
public void delete (int position) { 
if (getListAdapter().getCount() > 0) { 
ArrayAdapter<Lyric> adapter = getListAdapter(); 
Lyric lyric = adapter.getItem(position); 
datasource.deleteLyric(lyric); 
adapter.remove(lyric); 
} 
}
 
 
@Override 
@SuppressWarnings("unchecked") 
public ArrayAdapter<Lyric> getListAdapter() { 
return (ArrayAdapter<Lyric>) super.getListAdapter(); 
}
 
Add
Remove

Custom SQLiteOpenHelper
public class MySQLiteHelper extends SQLiteOpenHelper { 
 
public static final String TABLE_LYRICS = "lyrics"; 
public static final String COLUMN_ID = "_id"; 
public static final String COLUMN_LYRIC = "lyric"; 
 
private static final String DATABASE_NAME = "lyric.db"; 
private static final int DATABASE_VERSION = 1; 
 
// Database creation sql statement 
private static final String DATABASE_CREATE = "create table " 
+ TABLE_LYRICS + "( " + COLUMN_ID 
+ " integer primary key autoincrement, " + COLUMN_LYRIC 
+ " text not null);"; 
 
public MySQLiteHelper(Context context) { 
super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 
 
@Override 
public void onCreate(SQLiteDatabase database) { 
database.execSQL(DATABASE_CREATE); 
} 
 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
Log.w(MySQLiteHelper.class.getName(), 
"Upgrading database from version " + oldVersion + " to " 
+ newVersion + ", which will destroy all old data"); 
db.execSQL("DROP TABLE IF EXISTS " + TABLE_LYRICS); 
onCreate(db); 
} 
 
}

Lyric Datasource
public class LyricDataSource { 
 
// Database fields 
private SQLiteDatabase database; 
private MySQLiteHelper dbHelper; 
private String[] allColumns = { MySQLiteHelper.COLUMN_ID, 
MySQLiteHelper.COLUMN_LYRIC}; 
 
public LyricDataSource(Context context) { 
dbHelper = new MySQLiteHelper(context); 
} 
 
public void open() throws SQLException { 
database = dbHelper.getWritableDatabase(); 
} 
 
public void close() { 
dbHelper.close(); 
}
public List<Lyric> getAllLyrics() { 
List<Lyric> lyrics = new ArrayList<Lyric>(); 
 
Cursor cursor = database.query(MySQLiteHelper.TABLE_LYRICS, 
allColumns, null, null, null, null,
MySQLiteHelper.COLUMN_ID); 
cursor.moveToFirst(); 
while (!cursor.isAfterLast()) { 
Lyric lyric = cursorToLyric(cursor); 
lyrics.add(lyric); 
cursor.moveToNext(); 
} 
// Make sure to close the cursor 
cursor.close(); 
return lyrics; 
}
public Lyric createLyric(String lyric) { 
ContentValues values = new ContentValues(); 
values.put(MySQLiteHelper.COLUMN_LYRIC, lyric); 
long insertId = database.insert(MySQLiteHelper.TABLE_LYRICS, null, 
values); 
allColumns, MySQLiteHelper.COLUMN_ID + " = " +
insertId, null, 
null, null, null); 
Lyric newLyric = cursorToLyric(cursor); 
cursor.close(); 
return newLyric; 
} 
 
public void deleteLyric(Lyric lyric) { 
long id = lyric.getId(); 
database.delete(MySQLiteHelper.TABLE_LYRICS,
MySQLiteHelper.COLUMN_ID 
+ " = " + id, null); 
} 
 
public Lyric getLyricByValue(String lyricText) { 
allColumns, MySQLiteHelper.COLUMN_LYRIC + " = '" +
lyricText + "'" , null, null, null, null); 
if (!cursor.isAfterLast()) { 
lyric = cursorToLyric(cursor); 
} 
cursor.close(); 
return lyric; 
}
 
private Lyric cursorToLyric(Cursor cursor) { 
Lyric lyric = new Lyric(); 
lyric.setId(cursor.getLong(0)); 
lyric.setLyricText(cursor.getString(1)); 
return lyric; 
}

Using SQLite Pros
• No additional dependencies
• Built in programatic transaction management
• Built in creation and upgrade event handling

What happens when you add a couple ﬁelds?
 
 
 
 
} 
 
@Override 
} 
 
@Override 
onCreate(db); 
} 
 
}

Update the data model
public class Lyric { 
private long id; 
private String lyricText;
private String source;
private boolean isChorus; 
 
public long getId() { 
return id; 
} 
 
public void setId(long id) { 
this.id = id; 
} 
 
public String getLyricText() { 
} 
 
public void setLyricText(String lyricText) { 
this.lyricText = lyricText; 
}
// Additional Getter/Setters 
 
@Override 
} 
}

Update the Datasource
 
MySQLiteHelper.COLUMN_LYRIC,
MySQLiteHelper.COLUMN_SOURCE,
MySQLiteHelper.COLUMN_CHORUS}; 
 
} 
 
} 
 
}
 
} 
cursor.close(); 
return lyrics; 
}
values.put(MySQLiteHelper.COLUMN_CHORUS, isChorus ? 1 : 0); 
values.put(MySQLiteHelper.COLUMN_SOURCE, source); 
values); 
allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId,
null, 
cursor.close(); 
return newLyric; 
} 
 
database.delete(MySQLiteHelper.TABLE_LYRICS, MySQLiteHelper.COLUMN_ID 
+ " = " + id, null); 
} 
 
} 
cursor.close(); 
return lyric; 
}
 
lyric.setLyricText(cursor.getString(1));
lyric.setChorus(cursor.getInt(2) == 1); 
lyric.setSource(cursor.getString(3)); 
return lyric; 
}

Add the columns to our SQLiteOpenHelper
 
 
public static final String COLUMN_SOURCE = "source"; 
 
public static final String COLUMN_CHORUS = "isChorus"; 
 
 
private static final String DATABASE_CREATE = 
 
"create table " 
+ " integer primary key autoincrement, “ + COLUMN_LYRIC + " text
not null, " 
+ COLUMN_CHORUS + " text, " 
+ COLUMN_SOURCE + " integer, " 
+ " ); " 
; 
 
... 
 
}

How about a second table
 
 
 
public static final String TABLE_ARTISTS = "artists"; 
public static final String COLUMN_ARTIST_NAME = "name"; 
public static final String COLUMN_ARTIST_LABEL = "label"; 
 
 
"create table " 
+ TABLE_LYRICS + "( " + COLUMN_ID + " integer primary key autoincrement, " 
+ COLUMN_LYRIC + " text not null, " 
+ COLUMN_SOURCE + " integer " 
+ " ); " 
+ 
"create table " 
+ TABLE_ARTISTS + "( " + COLUMN_ID + " integer primary key autoincrement, " 
+ COLUMN_ARTIST_NAME + " text not null, " 
+ COLUMN_ARTIST_LABEL + " text " 
+ " ); " 
;
 
 
... 
 
}

Or a many to many relationship
 
 
 
public static final String TABLE_ARTISTS = "artists"; 
public static final String COLUMN_ARTIST_NAME = "name"; 
public static final String COLUMN_ARTIST_LABEL = “label";
public static final String TABLE_LYRIC_ARTIST = "lyric_artist"; 
public static final String COLUMN_LYRIC_ID = "lyric_id"; 
public static final String COLUMN_ARTIST_ID = "artist_id"; 
 
 
 
"create table " 
+ TABLE_LYRICS + "( " + COLUMN_ID + " integer primary key autoincrement, " 
+ COLUMN_LYRIC + " text not null, " 
+ COLUMN_SOURCE + " integer " 
+ " ); " 
+ 
"create table " 
+ TABLE_ARTISTS + "( " + COLUMN_ID + " integer primary key autoincrement, " 
+ COLUMN_ARTIST_NAME + " text not null, " 
+ COLUMN_ARTIST_LABEL + " text " 
+ " ); “
+ 
"create table " 
+ TABLE_LYRIC_ARTIST + "( " 
+ COLUMN_LYRIC_ID + " integer, " 
+ COLUMN_ARTIST_ID + " integer, " 
+ " FOREIGN KEY(" + COLUMN_ARTIST_ID + ") REFERENCES " + TABLE_ARTISTS + "(" + COLUMN_ID + "), " 
+ " FOREIGN KEY(" + COLUMN_LYRIC_ID + ") REFERENCES " + TABLE_LYRICS + "(" + COLUMN_ID + ") " 
+ " ); " 
;
 
 
... 
 
}

Using SQLite Cons
• Queries / Updates are very tedious
• Changes become cumbersome
• Relationships between an object graph must be manually
managed

Realm Mobile Database Replacement

About Realm
• Realm is a Mobile Database:
• A replacement for Core Data or SQLite
• Feels like an Object Relational Mapping tool
• Free & Open Source Apache 2.0
• Comparable Performance to SQLite

Fast Queries
https://realm.io/news/introducing-realm/

Faster Counts

Slower Inserts

Realm Objects Look like Regular Objects…
public class Dog extends RealmObject { 
 
private String name; 
private int age; 
@ignored private int dontPersistMe; 
 
// + Standard setters and getters here 
 
} 
 
@RealmClass
public class Person implements RealmModel { 
 
private String name; 
private RealmList<Dog> dogs; 
 
}

Easy to add / relate objects
try(Realm realm = Realm.getInstance(this.getContext())) { 
 
realm.beginTransaction(); 
 
Dog dog = realm.createObject(Dog.class); 
dog.setName("Rex"); 
dog.setAge(3); 
 
Person person = realm.createObject(Person.class); 
person.setName("Tim"); 
person.getDogs().add(dog); 
 
realm.commitTransaction(); 
}

Updates must be wrapped in transactions
 
 
dog.setAge(3); 
 
 
}

Updates must be wrapped in transactions
 
 
dog.setAge(3); 
 
 
}
If an exception occurs, you must catch it
and rollback with realm.cancelTransaction( );

1 to Many
 
 
dog.setAge(3); 
 
 
}
1 to Many

Many to Many
 
 
Dog rex = realm.createObject(Dog.class); 
rex.setName("Rex"); 
rex.setAge(3); 
 
Dog spot = realm.createObject(Dog.class); 
spot.setName("Spot"); 
spot.setAge(4); 
Person tim = realm.createObject(Person.class); 
tim.setName(“Tim");
tim.getDogs().addAll(Arrays.asList(spot, rex));
Person mary = realm.createObject(Person.class); 
mary.setName("Mary"); 
mary.getDogs().addAll(Arrays.asList(spot, rex)); 
rex.getOwners().addAll(Arrays.asList(tim, mary));
spot.getOwners().addAll(Arrays.asList(tim, mary));
 
}
Many to Many

Querying
// Queries uses Builder pattern to build up the query conditions
// For this example, assume Dog has a property “Person owner” 
RealmResults<Dog> results = realm.where(Dog.class) 
.greaterThan("age", 8)
.equalTo("owner.name", "Tim")
.findAll();
// Queries are chainable 
RealmResults<Dog> allRex = results.where()
.contains("name", "rex") 
.findAll();
// Or they can be combined 
RealmResults<Dog> result2 = realm.where(Dog.class)
.greaterThan("age", 8)
.equalTo(“owner.name", "Tim")
.contains("name", "rex")
.findAll();

More Queries
// Logical Query Grouping
boolean checkCase = false;
RealmResults<Dog> r = realm.where(Dog.class)
.greaterThan("age", 8) //implicit AND
.beginGroup()
.equalTo("name", “CuJo”, checkCase)
.or()
.contains("name", "rex")
.endGroup()
.findAll();
// Sorting
RealmResults<Dog> result = r.where(Dog.class).findAll(); 
result.sort("age"); // Sort ascending 
result.sort("age", RealmResults.SORT_ORDER_DESCENDING); 
// Result Aggregation
long sum = result.sum("age").longValue(); 
long min = result.min("age").longValue(); 
long max = result.max("age").longValue(); 
double average = result.average("age"); 
long matches = result.size();

Query Conditions
• between, greaterThan, lessThan,  
greaterThanOrEqualTo & lessThanOrEqualTo
• equalTo, notEqualTo, in, not & distinct
• contains, beginsWith & endsWith
• isNull & isNotNull
• isEmpty & isNotEmpty

Realm Object Field Types
• Java primitives
• Wrapper types
• byte[] for blob
• Realm Object
• RealmList<? extends RealmObject>

Realm Annotations
• @Required - Not Null
• @Ignore - Transient
• @PrimaryKey - string or integer (short, int or long)
• @Index - Implicitly set by Primary Key

Realm Installation
1. Add a classpath dependency to the project level build.grade ﬁle 
 
buildscript {

repositories {
jcenter()
}
dependencies {
classpath "io.realm:realm-gradle-plugin:2.1.1"
}
} 
2. Apply the realm-android plugin at the app module level build.grade ﬁle

apply plugin: 'realm-android'

Custom SQLiteOpenHelper Goes Away!
 
 
 
 
} 
 
@Override 
} 
 
@Override 
onCreate(db); 
} 
 
}

public class Lyric extends RealmObject { 
 
private int sortKey;
@PrimaryKey private String id; 
@Required private String lyricText; 
 
 
// Getters / Setters... 
 
@Override 
} 
}
Simple Data Object - Still Simple
RealmObject
and
Annotations

Lyric Datasource
 
MySQLiteHelper.COLUMN_LYRIC}; 
 
} 
 
} 
 
}
 
} 
cursor.close(); 
return lyrics; 
}
values); 
allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId,
null, 
cursor.close(); 
return newLyric; 
} 
 
System.out.println("Lyric deleted with id: " + id); 
database.delete(MySQLiteHelper.TABLE_LYRICS, MySQLiteHelper.COLUMN_ID 
+ " = " + id, null); 
} 
 
} 
cursor.close(); 
return lyric; 
}
 
lyric.setLyricText(cursor.getString(1)); 
return lyric; 
}

Lyric Datasource
private Realm r; 
 
public LyricDataSource(Realm realm) { 
r = realm; 
}
 
public void deleteAllLyrics() { 
r.executeTransaction(new Realm.Transaction() { 
@Override 
public void execute(Realm realm) { 
realm.delete(Lyric.class); 
} 
}); 
} 
 
return r.where(Lyric.class)
.equalTo("lyricText", lyricText)
.findFirst(); 
} 
 
return r.where(Lyric.class)
.findAllSorted("sortKey");
 
}
public Lyric createLyric(String lyricString) { 
final Lyric lyric = new Lyric(); 
lyric.setId(UUID.randomUUID().toString()); 
lyric.setLyricText(lyricString);
lyric.setSortKey(System.currentTimeMillis());
 
@Override 
lyric = realm.copyToRealm(lyric); 
} 
}); 
return lyric; 
} 
 
@Override 
realm.where(Lyric.class) 
.equalTo("id", lyric.getId()) 
.findAll() 
.deleteAllFromRealm(); 
} 
}); 
}

Application / Activity - Lifecycle Events
public class TestDatabaseActivity extends ListActivity { 
 
private LyricDataSource datasource;
private Realm realm;
 
@Override 
public void onCreate(Bundle savedInstanceState) { 
setContentView(R.layout.main); 
realm = Realm.getDefaultInstance(); 
datasource = new LyricDataSource(realm); 
 
 
ArrayAdapter<Lyric> adapter =
new ArrayAdapter<Lyric>(this, 
android.R.layout.simple_list_item_1,
values); 
setListAdapter(adapter); 
} 
 
@Override 
protected void onDestroy() { 
super.onDestory(); 
realm.close(); 
} 
...
}
public class NaeNaeApplication extends Application { 
 
@Override 
public void onCreate() { 
super.onCreate(); 
Realm.init(this);
RealmConfiguration realmConfiguration = 
new RealmConfiguration.Builder() 
.deleteRealmIfMigrationNeeded() 
.build(); 
Realm.setDefaultConfiguration(realmConfiguration); 
} 
 
}

 
 
@Override 
 
 
values); 
} 
 
@Override 
realm.close(); 
} 
...
}
Keep reference
Get new instance of
realm datasource
on create and pass
to the datasource to
use.
1
 
@Override 
Realm.init(this);
.build(); 
} 
 
}

 
 
@Override 
 
 
values); 
} 
 
@Override 
realm.close(); 
} 
...
}
Keep reference
Get new instance of
realm datasource
on create and pass
use.
For
getDefaultInstance
to work, we must
set the default
conﬁguration once
1
2
 
@Override 
Realm.init(this);
.build(); 
} 
 
}

 
 
@Override 
 
 
values); 
} 
 
@Override 
realm.close(); 
} 
...
} Close on destroy
Keep reference
Get new instance of
realm datasource
on create and pass
use.
For
getDefaultInstance
to work, we must
set the default
conﬁguration once
1
2
3
 
@Override 
Realm.init(this);
.build(); 
} 
 
}

Checkpoint
• Remove SQLite DataHelper
• Made our datasource code easier to read
• Reduced Code:
SQLite Realm
Lyric 28 40
Activity 77 72
DataSource 92 61
MySQLiteHelper 41 0
Application
0 21
Total 238 194

Change Listeners
public class MyActivity extends Activity { 
private Realm realm; 
private RealmChangeListener<RealmResults<Lyric>> listener; 
private RealmResults<Lyric> lyrics; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
lyrics = realm.where(Lyric.class).contains("lyricText", "Bop").findAll(); 
listener = new RealmChangeListener<RealmResults<Lyric>>() { 
@Override 
public void onChange(RealmResults<Lyric> updatedResults) { 
// Do something with the updated results, actually the results here 
// match the ones stored as a reference in this activity. 
} 
}; 
lyrics.addChangeListener(listener); 
} 
 
@Override 
super.onDestroy(); 
realm.removeAllChangeListeners(); 
realm.close(); 
}
}

Async Operations
// Async with Callback
private RealmChangeListener callback = new RealmChangeListener() { 
@Override 
public void onChange() { // called once the query complete and on every update 
// use the result 
} 
}; 
public void onStart() { 
try(Realm r = Realm.getInstance(context)) { 
RealmResults<Lyric> result = r.where(Lyric.class).findAllAsync(); 
result.addChangeListener(callback); 
} 
}
// Or you can block (be careful)
while (!result.isLoaded()) { 
// Results are now available 
}
// Or to block until async results are loaded
result.load()

Transaction Blocks & Async Transactions
// Transaction will be committed after block unless exception occurs.
realm.executeTransaction(new Realm.Transaction() { 
@Override 
Lyric user = realm.createObject(Lyric.class); 
user.setId(UUID.randomUUID().toString()); 
user.setLyricText("Let's get it started!"); 
} 
}); 
// Asynchronous Transaction
realm.executeTransactionAsync(new Realm.Transaction() { 
@Override 
public void execute(Realm bgRealm) { 
Lyric user = bgRealm.createObject(Lyric.class); 
 
user.setId(UUID.randomUUID().toString()); 
 
user.setLyricText("Let's get it started in here"); 
 
} 
}, new Realm.Transaction.OnSuccess() { 
@Override 
public void onSuccess() { 
// Do something on the thread you were on. 
} 
}, new Realm.Transaction.OnError() { 
@Override 
public void onError(Throwable error) { 
// Transaction failed and was automatically canceled. 
// Do something on the thread you were on. 
} 
});

Insert JSON Directly
// Insert from a string 
r.beginTransaction(); 
r.createObjectFromJson(Lyric.class, 
"{ lyricText: "Bidi-bidi-bop", " + 
"id: "864dee8a-d9ac-4e5a-a843-e051ad2d6e8a" }"); 
r.commitTransaction(); 
 
// Insert multiple items using a InputStream 
InputStream is = new FileInputStream(new File("path_to_file")); 
r.beginTransaction(); 
try { 
r.createAllFromJson(Lyric.class, is); 
r.commitTransaction(); 
} catch (IOException e) { 
r.cancelTransaction(); 
}

ListAdapter & Recycler Adapters
dependencies {
compile ‘io.realm:android-adapters:1.4.0'
}

dependencies {
}
public class MyAdapter extends RealmBaseAdapter<Lyric> implements ListAdapter { 
 
private static class ViewHolder { 
TextView lyricTextView; 
} 
public MyAdapter(Context context, int resId, 
RealmResults<Lyric> realmResults, 
boolean automaticUpdate) { 
super(context, realmResults, automaticUpdate); 
} 
 
@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
ViewHolder viewHolder; 
if (convertView == null) { 
convertView = inflater.inflate(android.R.layout.simple_list_item_1, 
parent, false); 
viewHolder = new ViewHolder(); 
viewHolder.lyricTextView = (TextView) convertView.findViewById(android.R.id.text1); 
convertView.setTag(viewHolder); 
} else { 
viewHolder = (ViewHolder) convertView.getTag(); 
} 
 
Lyric item = realmResults.get(position); 
viewHolder.lyricTextView.setText(item.getLyricText()); 
return convertView; 
} 
 
public RealmResults<Lyric> getRealmResults() { 
return realmResults; 
} 
}

dependencies {
}
MyRecyclerViewAdapter extends RealmRecyclerViewAdapter<Promotion, MyRecyclerViewAdapter.ViewHolder> { 
 
private final MyActivity activity; 
 
public RealmRecyclerViewAdapter(@NonNull MyActivity activity, @Nullable OrderedRealmCollection<Lyric> lyrics)
{ 
super(promoListActivity, lyrics, true); 
this.activity = activity; 
} 
 
@Override 
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
View view = LayoutInflater.from(parent.getContext()) 
.inflate(R.layout.lyric_list_item, parent, false); 
return new ViewHolder(view); 
} 
 
@Override 
public void onBindViewHolder(final ViewHolder holder, int position) { 
Lyric lyric = getData().get(position); 
holder.lyrcTextView.setText(lyric.getLyricText());
holder.lyricId = lyric.getId()); 
} 
 
public class ViewHolder extends RecyclerView.ViewHolder { 
public TextView titleView; 
public String promotionId; 
 
public ViewHolder(View view) { 
super(view); 
lyricTextView = (TextView) view.findViewById(R.id.lyric_itle); 
} 
}

Encryption
RealmConfiguration config = new RealmConfiguration.Builder(context) 
.encryptionKey(getKey()) 
.build();
• The Realm ﬁle can be stored encrypted on disk by
passing an encryption key (byte [])
• All data persisted to disk is transparently encrypted and
decrypted with standard AES-256 encryption

Migrations
.schemaVersion(2) // Must be bumped when the schema changes 
.migration(new MyMigration()) // Migration handler class 
.build();
• Bump the version with each change
• Point the RealmConﬁguration to you custom
RealmMigration Implementation

Migrations
.schemaVersion(2) // Must be bumped when the schema changes 
.migration(new MyMigration()) // Migration handler class 
.build();
public class MyMigration implements RealmMigration { 
public void migrate(DynamicRealm realm, long oldVersion, long newVersion) { 
 
RealmSchema schema = realm.getSchema(); // DynamicRealm exposes an editable schema 
 
if (oldVersion == 0) { // Migrate to version 1: Add a new class 
schema.create("Person") 
.addField("name", String.class) 
.addField("age", int.class); 
oldVersion++; // Bump the version after each updgrade 
} 
 
if (oldVersion == 1) { // Migrate to version 2: Add PK + relationships 
schema.get("Person") 
.addField("id", long.class, FieldAttribute.PRIMARY_KEY) 
.addRealmObjectField("favoriteDog", schema.get("Dog")) 
.addRealmListField("dogs", schema.get("Dog")); 
oldVersion++; 
} 
} 
}

Migrations
public class MyMigration implements RealmMigration { 
public void migrate(DynamicRealm realm, long oldVersion, long newVersion) { 
 
RealmSchema schema = realm.getSchema(); // DynamicRealm exposes an editable schema 
 
if (oldVersion == 0) { // Migrate to version 1: Add a new class 
schema.create("Person") 
.addField("name", String.class) 
.addField("age", int.class); 
oldVersion++; // Bump the version after each updgrade 
} 
 
if (oldVersion == 1) { // Migrate to version 2: Add PK + relationships 
schema.get("Person") 
.addField("id", long.class, FieldAttribute.PRIMARY_KEY) 
.addRealmObjectField("favoriteDog", schema.get("Dog")) 
.addRealmListField("dogs", schema.get("Dog")); 
oldVersion++; 
} 
} 
}

Resources
• Realm - https://realm.io/
• Source Code - https://github.com/realm/realm-java
• Code Samples
• Presentation Examples 
https://github.com/ericmaxwell2003/
roboguiceRealmNaeNae
• Credible Software - http://credible.software

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