Groovy and Android: a winning pair

Talk given at MCE 2015, Warsaw, about using Groovy to develop Android applications.

Transcript

1. #GroovyAndroid @CedricChampeau
   Groovy & Android
   A winning pair
   By Cédric Champeau
   

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2. #GroovyAndroid @CedricChampeau 2/47
   whoami.groovy
   def speaker = new Speaker(
   name: 'Cedric Champeau',
   employer: 'Pivotal',
   occupation: 'Core Groovy committer',
   successes: ['Static type checker',
   'Static compilation',
   'Traits',
   'Markup template engine',
   'DSLs'],
   failures: Stream.of(bugs),
   twitter: '@CedricChampeau',
   github: 'melix',
   extraDescription: '''Groovy in Action 2 co-
   author
   Misc OSS contribs (Gradle plugins,
   deck2pdf, jlangdetect, ...)'''
   )
   

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3. #GroovyAndroid @CedricChampeau 3/47
   Why Android?
   • Uses a JVM
   • SDK is free
   • Tooling also freely available
   (Android Studio)
   • Swift anyone?
   

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4. #GroovyAndroid @CedricChampeau 4/47
   Why Groovy?
   • Built on top of the shoulders of a Giant (Java)
   • Runs a JVM
   • Android developers shouldn't be suffering
   • Java on Android is very verbose
   • And the main development language on the platform
   • Multi-faceted language
   • OO, Imperative, functional, scripting, dynamic, static,
   …
   • Straightforward integration with Java
   

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5. #GroovyAndroid @CedricChampeau 5/47
   Why Groovy?
   button.setOnClickListener(new
   View.OnClickListener() {
   @Override
   void onClick(View v) {
   startActivity(intent);
   }
   }) button.onClickListener = {
   startActivity(intent)
   }
   

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6. #GroovyAndroid @CedricChampeau 6/47
   Why Groovy?
   @RestableEntity
   @ToString
   class User {
   String name
   String phone
   String avatar
   Integer balance
   static constraints = {
   name pattern: ~/[a-zA-Z]+/, min: 3, max: 5, blank: false,
   nullable: false
   phone pattern: ~/\d+/, size: 2..4
   balance range: 10..100
   }
   }
   Groovy Beans
   Grails-like entities
   

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7. #GroovyAndroid @CedricChampeau 7/47
   @CompileStatic
   @SelfType(Context)
   trait GoogleApiProvider {
   GoogleApiClient googleApiClient
   void createGoogleApi() {
   googleApiClient = new GoogleApiClient.Builder(this)
   .addApi(Wearable.API)
   .build()
   }
   ...
   }
   Why Groovy?
   

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8. #GroovyAndroid @CedricChampeau 8/47
   class CountDownService extends Service implements GoogleApiProvider {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState)
   contentView = R.layout.activity_presentation
   createGoogleApi()
   }
   // ...
   }
   class StartPresentationActivity extends Activity implements GoogleApiProvider {
   // ...
   }
   class WearPresentationActivity extends Activity implements GoogleApiProvider,
   MessageApi.MessageListener {
   // ...
   }
   Why Groovy?
   

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9. #GroovyAndroid @CedricChampeau 9/47
   Intent viewIntent = new Intent(this, WearPresentationActivity.class);
   PendingIntent viewPendingIntent =
   PendingIntent.getActivity(
   this,
   0,
   viewIntent,
   FLAG_UPDATE_CURRENT);
   NotificationCompat.BigTextStyle bigStyle = new NotificationCompat.BigTextStyle();
   bigStyle.bigText("Time left for your presentation: "+timeLeft+"\n"+
   "Elapsed time: "+rounded+"%");
   NotificationCompat.Builder notificationBuilder=
   new NotificationCompat.Builder(this);
   notificationBuilder.setSmallIcon(R.drawable.ic_action_alarms)
   .setLargeIcon(BitmapFactory.decodeResource(getResources(),R.drawable.speaker))
   .setContentTitle("Time left")
   .setContentText(timeLeft+" (Elapsed: "+rounded+"%)")
   .setContentIntent(viewPendingIntent)
   .setStyle(bigStyle);
   NotificationManagerCompat notificationManager=
   NotificationManagerCompat.from(this);
   notificationManager.notify(NOTIFICATION_ID,notificationBuilder.build());
   Why Groovy?
   

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10. #GroovyAndroid @CedricChampeau 10/47
    notify(NOTIFICATION_ID) {
    smallIcon = R.drawable.ic_action_alarms
    largeIcon = cachedBitmap
    contentTitle = 'Time left'
    contentText = "$timeLeft (Elapsed: ${rounded}%)"
    contentIntent = pendingActivityIntent(0,
    intent(WearPresentationActivity), FLAG_UPDATE_CURRENT)
    ongoing = true
    style = bigTextStyle {
    bigText """Time left for your presentation: $timeLeft
    Elapsed time: ${rounded}%)
    """
    }
    }
    Why Groovy?
    

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11. #GroovyAndroid @CedricChampeau 11/47
    @CompileStatic
    class ContextGroovyMethods {
    static NotificationManagerCompat getCompatNotificationManager(Context self) {
    NotificationManagerCompat.from(self)
    }
    static void notify(Context self, int notificationId, Notification notification) {
    getCompatNotificationManager(self).notify(notificationId, notification)
    }
    static Notification notification(Context self, @DelegatesTo(NotificationCompat.Builder) Closure
    notificationSpec) {
    def builder = new NotificationCompat.Builder(self)
    builder.with(notificationSpec)
    builder.build()
    }
    static void notify(Context self, int notificationId, @DelegatesTo(NotificationCompat.Builder) Closure
    notificationSpec) {
    notify(self, notificationId, notification(self, notificationSpec))
    }
    ...
    }
    Why Groovy?
    

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12. #GroovyAndroid @CedricChampeau 12/47
    private @Lazy Bitmap cachedBitmap =
    BitmapFactory.decodeResource(resources, R.drawable.speaker)
    Why Groovy?
    

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13. #GroovyAndroid @CedricChampeau 13/47
    SpeakerTime
    github.com/melix/speakertime
    

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14. #GroovyAndroid @CedricChampeau 14/47
    Groovy on Android: the problems
    • Groovy is primarily a dynamic language
    • Not everything done at compile time
    • Intensive use of reflection
    • Potentially slow invocation pathes
    • Battery?
    • Bytecode is different
    • Classes at runtime?
    

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15. #GroovyAndroid @CedricChampeau 15/47
    • Not all classes are available
    • java.bean.xxx very problematic
    • Multiple runtimes
    • Dalvik
    • ART
    • Behavior not the same as the standard JVM
    Groovy on Android: the problems
    

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16. #GroovyAndroid @CedricChampeau 16/47
    Groovy on Android: dex files
    • Dalvik VM = alternative bytecode
    • Groovy generates JVM bytecode
    • Translation done through dex
    • No native support for generating classes
    at runtime
    

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17. #GroovyAndroid @CedricChampeau 17/47
    Compiling an Android application
    • Classic process
    

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18. #GroovyAndroid @CedricChampeau 18/47
    • Classic process for a Groovy application
    Compiling an Android application
    

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19. #GroovyAndroid @CedricChampeau 19/47
    Compiling an Android application
    • Runtime generation of classes
    

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20. #GroovyAndroid @CedricChampeau 20/47
    Classes at runtime?!
    • Works, but very slow
    • Lots of I/O involved
    • What about ASMDex?
    • Same approach used by Ruboto
    • Nice proof of concept
    

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21. #GroovyAndroid @CedricChampeau 21/47
    Redefinining
    objectives
    

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22. #GroovyAndroid @CedricChampeau 22/47
    Groovy 2.4: Objectives for Android
    • Supporting Android in the standard distribution
    • Building a full Android application in Groovy
    • Main focus on @CompileStatic
    • Optional use of dynamic Groovy
    • No performance issue!
    

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23. #GroovyAndroid @CedricChampeau 23/47
    Groovy 2.4: Objectives for community
    • Community is a major strenght of Groovy
    • We need you for Android too!
    • Bring the goodness of Groovy to Android
    • Invent new frameworks!
    

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24. #GroovyAndroid @CedricChampeau 24/47
    

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25. #GroovyAndroid @CedricChampeau 25/47
    github.com/melix/grooidshell-example
    

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26. #GroovyAndroid @CedricChampeau 26/47
    Requirements
    • Gradle
    • Android Studio
    • Or your favorite editor...
    • Groovy 2.4.0 (“grooid”)
    • A good tutorial on Android...
    

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27. #GroovyAndroid @CedricChampeau 27/47
    Groovy 2.4 Android Support
    • Must use a specific Android jar
    • Use of the grooid classifier
    • Replaces java.beans use with openbeans
    • Workarounds for Android specific behavior
    • Reduced number of methods in bytecode
    • Important for the 64k limit of dex files
    

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28. #GroovyAndroid @CedricChampeau 28/47
    Gradle plugin
    • Gradle is the new default build system for
    Android
    • apply plugin: 'com.android.application'
    • Uses a non standard compilation process
    • Without Groovy specific plugin, lots of trickery
    involved
    • Thus use a plugin: apply plugin:
    'groovyx.grooid.groovy-android'
    • Supports both the application and library plugins
    

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29. #GroovyAndroid @CedricChampeau 29/47
    Gradle plugin
    buildscript {
    repositories {
    jcenter()
    }
    dependencies {
    classpath 'com.android.tools.build:gradle:0.14.0'
    classpath 'org.codehaus.groovy:gradle-groovy-android-plugin:0.3.5'
    }
    }
    apply plugin: 'groovyx.grooid.groovy-android'
    dependencies {
    compile 'org.codehaus.groovy:groovy:2.4.0:grooid'
    }
    

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30. #GroovyAndroid @CedricChampeau 30/47
    Then code!
    @CompileStatic
    @ToString(includeNames = true)
    @EqualsAndHashCode
    class Session {
    Long id
    Long speakerId
    Slot slot
    String title
    String summary
    List tags
    }
    

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31. #GroovyAndroid @CedricChampeau 31/47
    Groovifying Android APIs
    class FeedTask extends AsyncTask {
    protected String doInBackground(String... params) {
    // very long boilerplate code....
    }
    @Override
    protected void onPostExecute(String s) {
    mTextView.setText(s);
    }
    }
    

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32. #GroovyAndroid @CedricChampeau 32/47
    Groovifying Android APIs
    32
    Fluent.async {
    def json = new JsonSlurper().parse([:],
    new URL('http://path/to/feed'), 'utf-8')
    json.speakers.join(' ')
    } then {
    mTextView.text = it
    }
    

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33. #GroovyAndroid @CedricChampeau 33/47
    Performance?
    

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34. #GroovyAndroid @CedricChampeau 34/47
    System resources
    • Example of the GR8Conf Agenda
    application
    • Groovy jar: 4.5MB
    • Application size: 2MB!
    • After ProGuard: only 1MB!
    • ~8.2MB of RAM! (but lots of images)
    

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35. #GroovyAndroid @CedricChampeau 35/47
    Community
    

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36. #GroovyAndroid @CedricChampeau 36/47
    Community projects
    • Community is more important than the
    language
    • New frameworks to invent
    • Some already did!
    

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37. #GroovyAndroid @CedricChampeau 37/47
    SwissKnife
    • Combines ideas from Android
    Annotations and ButterKnife
    • Based on AST transformations
    • View injection
    • Threading model
    • Bundles management
    • Works with annotations to generate code
    

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38. #GroovyAndroid @CedricChampeau 38/47
    SwissKnife
    class MyActivity extends Activity {
    @ViewById(R.id.myField) TextField mTextField
    @OnClick(R.id.button)
    void onButtonClicked(Button button) {
    Toast.makeText(this, "Button clicked", Toast.LENGTH_SHOT).show()
    }
    @OnBackground
    void doSomeProcessing(URL url) {
    // Contents will be executed on background
    ...
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState)
    contentView = R.layout.activity_main
    // This must be called for injection of views and callbacks to take place
    SwissKnife.inject(this)
    }
    }
    

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39. #GroovyAndroid @CedricChampeau 39/47
    SwissKnife
    @SaveInstance
    private int myInt
    // You can also set a custom tag to your variable
    @SaveInstance("MYSTRING")
    private String myString
    @Override
    void onCreate(Bundle savedInstanceState){
    // Your previous code
    SwissKnife.restoreState(this, savedInstanceState)
    }
    

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40. #GroovyAndroid @CedricChampeau 40/47
    SwissKnife
    public class ParcelableClass implements Parcelable {
    private int id;
    private String name;
    public ParcelableClass(Parcel source) {
    this.id = source.readInt();
    this.name = source.readString();
    }
    public void writeToParcel(Parcel out) {
    out.writeInt(id);
    out.writeString(name);
    }
    public String getId() { return id; }
    // ...
    }
    

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41. #GroovyAndroid @CedricChampeau 41/47
    SwissKnife
    @Parcelable
    class ParcelableClass {
    int id
    String name
    }
    

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42. #GroovyAndroid @CedricChampeau 42/47
    Grooid Tools
    View view = new AndroidBuilder().build(this) {
    relativeLayout(width: MATCH_PARENT, height: MATCH_PARENT, padding: [dp(64), dp(16)]) {
    textView(width: MATCH_PARENT, height: dp(20), text: R.string.hello_world)
    }
    }
    • Builders for views
    • Experimental
    • https://github.com/karfunkel/grooid-tools
    

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43. #GroovyAndroid @CedricChampeau 43/47
    Potential issues
    • Performance of dynamic Groovy on low end-devices
    • Use @CompileStatic whenever possible
    • The infamous 64k method count
    • Use ProGuard and multidex support
    • Tooling support
    • Groovy not fully supported by Android Studio
    • Google support
    • Android Gradle plugin updates are very frequent
    

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44. #GroovyAndroid @CedricChampeau 44/47
    “Best of all, I expect to try to update
    Android Studio right before the talk, so
    I have the latest possible version in the
    so­called Canary channel. What could
    possibly go wrong?”
    Ken Kousen, September 10th, 2014
    

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45. #GroovyAndroid @CedricChampeau 45/47
    Other ideas
    • Dagger-like dependency injection
    framework?
    • Dagger 2 in the works...
    • Data binding APIs
    • Improved reactive APIs
    • You can already use Reactor or RxJava
    

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46. #GroovyAndroid @CedricChampeau 46/47
    Future is now!
    • New York Times next app being written in Groovy!
    

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47. #GroovyAndroid @CedricChampeau
    @CedricChampeau
    melix
    http://melix.github.io/blog
    

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