Essential Books

Basic Usage

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Setting up an instance

To use Realm you first need to obtain an instance of it. Each Realm instance maps to a file on disk. The most basic way to get an instance is as follows: 

// Create configuration
RealmConfiguration realmConfiguration = new RealmConfiguration.Builder(context).build();

// Obtain realm instance
Realm realm = Realm.getInstance(realmConfiguration);
// or
Realm.setDefaultConfiguration(realmConfiguration);
Realm realm = Realm.getDefaultInstance();

The method Realm.getInstance() creates the database file if it has not been created, otherwise opens the file. The RealmConfiguration object controls all aspects of how a Realm is created - whether it’s an inMemory() database, name of the Realm file, if the Realm should be cleared if a migration is needed, initial data, etc.

Please note that calls to Realm.getInstance() are reference counted (each call increments a counter), and the counter is decremented when realm.close() is called.

Closing an instance

On background threads, it’s very important to close the Realm instance(s) once it’s no longer used (for example, transaction is complete and the thread execution ends). Failure to close all Realm instances on background thread results in version pinning, and can cause a large growth in file size. 

Runnable runnable = new Runnable() {
    Realm realm = null;
    try {
        realm = Realm.getDefaultInstance();
        // ...
    } finally {
        if(realm != null) {
            realm.close();
        }
    }
};

new Thread(runnable).start(); // background thread, like `doInBackground()` of AsyncTask

It’s worth noting that above API Level 19, you can replace this code with just this: 

try(Realm realm = Realm.getDefaultInstance()) {
    // ...
}

Models

Next step would be creating your models. Here a question might be asked, “what is a model?”. A model is a structure which defines properties of an object being stored in the database. For example, in the following we model a book. 

public class Book extends RealmObject {
 
    // Primary key of this entity
    @PrimaryKey
    private long id;
 
    private String title;

    @Index // faster queries
    private String author;
 
    // Standard getters & setter
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
    public String getTitle() {
        return title;
    }
 
    public void setTitle(String title) {
        this.title = title;
    }
 
    public String getAuthor() {
        return author;
    }
 
    public void setAuthor(String author) {
        this.author = author;
    }
}

Note that your models should extend RealmObject class. Primary key is also specified by @PrimaryKey annotation. Primary keys can be null, but only one element can have null as a primary key. Also you can use the @Ignore annotation for the fields that should not be persisted to the disk: 

@Ignore
private String isbn;

Inserting or updating data

In order to store a book object to your Realm database instance, you can first create an instance of your model and then store it to the database via copyToRealm method. For creating or updating you can use copyToRealmOrUpdate. (A faster alternative is the newly added insertOrUpdate()). 

// Creating an instance of the model
Book book = new Book();
book.setId(1);
book.setTitle("Walking on air");
book.setAuthor("Taylor Swift")

// Store to the database
realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        realm.insertOrUpdate(book);
    }
});

Note that all changes to data must happen in a transaction. Another way to create an object is using the following pattern: 

Book book = realm.createObject(Book.class, primaryKey);
...

Querying the database 

RealmResults<Book> results = realm.where(Book.class).findAll();
RealmResults<Book> results = realm.where(Book.class)
                                  .greaterThan("id", 10)
                                  .findAll();
RealmResults<Book> results = realm.where(Book.class)
                                  .beginGroup()
                                      .equalTo("author", "Taylor Swift")
                                      .or()
                                      .contains("author", "Peter")
                                  .endGroup().findAll();

Deleting an object

For example, we want to delete all books by Taylor Swift: 

// Start of transaction
realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        // First Step: Query all Taylor Swift books
        RealmResults<Book> results = ...
        
        // Second Step: Delete elements in Realm
        results.deleteAllFromRealm();
    }
});
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Realm:
* Realm
* Sorted queries
* Using Realm with RxJava
* Basic Usage
* List of primitives RealmListIntegerString...
* Async queries
* Adding Realm to your project
* Realm Models
* try-with-resources
Table Of Contents
0 Getting Started
1 Layouts
2 Gradle
3 RecyclerView onClickListeners
4 NavigationView
5 Intent
6 JSON handling with org.json
7 Android Studio
8 Resources
9 Data Binding Library
10 Exceptions
11 Getting Calculated View Dimensions
12 AsyncTask
13 SharedPreferences
14 Emulator
15 Material Design
16 Lint Warnings
17 Service
18 Storing Files in Internal and External Storage
19 WebView
20 Project SDK versions
21 RecyclerView
22 Google Maps
23 PorterDuff Mode
24 9-Patch images
25 Android NDK
26 RecyclerView Decorations
27 Camera 2 API
28 ViewPager
29 CardView
30 HttpURLConnection
31 SQLite
32 ADB Android Debug Bridge
33 ButterKnife
34 Supporting different screen resolutions
35 Glide
36 Retrofit2
37 Dialog
38 ACRA
39 GreenDAO
40 Formatting Strings
41 Notifications
42 AlarmManager
43 Fragments
44 Handler
45 Creating Custom Views
46 BroadcastReceiver
47 Activity
48 Snackbar
49 Runtime Permissions in API-23
50 Logging and using Logcat
51 VectorDrawable and AnimatedVectorDrawable
52 Tools Attributes
53 Toast
54 Interfaces
55 Animators
56 Location
57 Theme Style Attribute
58 The Manifest File
59 Parcelable
60 MediaPlayer
61 Multidex and the Dex Method Limit
62 Data Synchronization with Sync Adapter
63 Menu
64 Instant Run in Android Studio
65 Picasso
66 Bluetooth LE API
67 RoboGuice
68 Memory Leaks
69 Universal Image Loader
70 Volley
71 Widgets
72 Date and Time Pickers
73 Integrate Google Sign In
74 In-app billing
75 FloatingActionButton
76 ContentProvider
77 Dagger 2
78 Realm
79 Unit testing in Android with JUnit
80 Android Versions
81 Wi-Fi Connections
82 SensorManager
83 Localization with resources
84 ProgressBar
85 Custom Fonts
86 Vibration
87 Google Awarness APIs
88 Text to Speech (TTS)
89 UI Lifecycle
90 Spinner
91 Data Encryption / Decryption
92 Testing UI with Espresso
93 Writing UI tests
94 GreenRobot EventBus
95 OkHttp
96 Enhancing Performance Using Icon Fonts
97 Handling Depp Links
98 Canvas drawing using SurfaceView
99 Firebase
100 Crash Reporting Tools
101 Check Internet Connectivity
102 Facebook SDK
103 Unzip File
104 Android Places API
105 Creating your own libraries
106 Handling JSON with Gson
107 Device Display Metrics
108 TextView
109 ListView
110 Building Backwards Compatible Apps
111 Loader
112 ProGuard - Obfuscating and Shrinking your code
113 Detect Shake Event
114 Typedef Annotations
115 Capturing Screenshots
116 MVP Architecture
117 Orientation Changes
118 Xposed
119 Security
120 PackageManager
121 ImageView
122 Gesture Detection
123 Doze Mode
124 Android Sound and Media
125 SearchView
126 Camera and Gallery
127 Callback URL
128 Twitter APIs
129 SqlCipher integration
130 Drawables
131 Colors
132 ConstraintLayout
133 RenderScript
134 Fresco
135 Swipe to Refresh
136 AutoCompleteTextView
137 Installing apps with ADB
138 IntentService
139 AdMob
140 Implicit Intents
141 Publish to Play Store
142 Firebase Realtime Database
143 Image Compression
144 Email Validation
145 Keyboard
146 Button
147 TextInputLayout
148 Bottom Sheets
149 CoordinatorLayout and Behaviors
150 EditText
151 Paypal Gateway Integration
152 Firebase App Indexing
153 Firebase Crash Reporting
154 Displaying Google Ads
155 Vk SDK
156 Localized DateTime
157 Count Down Timer
158 Reading Barcode and QR codes
159 Otto Event Bus
160 TransitionDrawable
161 Port Mapping using Cling
162 Creating Overlay always-on-top Windows
163 ExoPlayer
164 Inter-app UI testing with UIAutomator
165 MediaSession
166 Speech to Text Conversion
167 FileProvider
168 Publish .aar file to Apache Archive with Gradle
169 XMPP
170 Authenticator
171 RecyclerView and LayoutManagers
172 AudioManager
173 Job Scheduling
174 Accounts and AccountManager
175 OpenCV
176 Split Screen Multi-Screen Activities
177 Threads
178 MediaStore
179 Time Utils
180 Touch Events
181 Fingerprint API
182 MVVM Architecture
183 BottomNavigationView
184 ORMLite
185 YouTube API
186 TabLayout
187 Retrofit2 with RxJava
188 DayNight Theme AppCompat
189 ShortcutManager
190 LruCache
191 Using Jenkins CI
192 Zip files
193 Vector Drawables
194 Fastlane
195 Define step value for RangeSeekBar
196 Getting started with OpenGL ES 2.0
197 Check Data Connection
198 Java Native Interface (JNI)
199 FileIO
200 Perfomance Optimization
201 Robolectric
202 Moshi
203 Strick Mode Policy
204 Internalization and localization
205 Retrolambda
206 SparseArray
207 Firebase Cloud Messaging
208 Shared Element Transitions
209 Android Things
210 VideoView
211 ViewFlipper
212 Dependency Injection with Dagger 2
213 Formatting phone numbers
214 Storing password securely
215 Android Kernel Optimization
216 Paint
217 AudioTrack
218 ProGuard
219 Create Android Custom ROMs
220 Java on Android
221 Pagination in RecyclerVi
222 Genymotion for Android
223 Handling touch and motion events
224 Creating Splash screen
225 ConstraintSet
226 CleverTap
227 Publish library to Maven repositories
228 ADB shell
229 Ping ICMP
230 AIDL
231 Using Kotlin
232 Autosizing TextView
233 Signing apps for release
234 Context
235 Activity Recognition
236 Secure SharedPreferences
237 Secure SharedPreferences
238 Bitmap Cache
239 Android x86 in VirtualBox
240 JCodec
241 Design Patterns
242 Okio
243 Google SignIn integration
244 TensorFlow
245 Game developmen
246 Notification Channel
247 Bluetooth Low Energy (LE)
248 Leak Canary
249 FuseView
250 SQLite using ContentValues
251 Enhancing Alert Dialogs
252 Hardware Button Events, Intents PTT
253 SpannableString
254 Looper
255 Optimized VideoView
256 Google Drive API
257 Animated AlertDialog Box
258 Annotation Processor
259 SyncAdapter with periodically do sync of data
260 Singleton Class for Toast Message
261 Fastjson
262 Android Architecture Components
263 Jackson
264 Play Store
265 Loading Bitmaps Effectively
266 Getting system font names
267 Smartcard
268 Convert vietnamese string to english
269 Contributors