Scala on-android
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Scala on Android: My Experience

Scala on Android: My Experience

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    Scala on-android Scala on-android Presentation Transcript

    • Scala on Android
    • Android Development● Write lots of Java code● Write UI and other resources in XML● Generate Java code from resources● Compile Java code into “.class” files● Run proguard● Compile class files to Dalvik Executable (DEX)● Deploy on device
    • Dalvik VM● Does not support “.class” bytecode format● Can not use libraries which generate bytecode● Devices have limited CPU and Memory● Can not easily share libraries between applications
    • Eclipse● Has nice UI editors● IDE is a build tool
    • Alternative Languages for Android
    • Jython● Does not have enough community support● Slow● Dynamic
    • JRuby● Ruboto framework● Dynamic● Need to use java code generation
    • Clojure● Very cool :)● Very slow start-up time● Sometimes need to generate bytecode
    • PHPWho cares?
    • Rhino● Nice language● Can run with optimization turned off● Completely interpreted● Dynamic
    • Groovy ???
    • Scala● Statically typed● Compiled to Java bytecode● Has access to all classes in Android● Fast ● but sometimes slow :)● Has SBT ● Android ● Maven artifacts
    • How to build Scala apps for Android● ANT● Maven● SBT + Android Plugin
    • Little nice things about Scala
    • Type Inference● Improve readability● Reduce number of imports● Less typing
    • val stream = getAssets().open("areas.json") val stream: InputStream = getAssets().open("areas.json")
    • Import statementimport android.view.{ Window, Menu, MenuItem, KeyEvent, View}import android.util.Log.{e => error}
    • Lazy valslazy val searchBox = findViewById(R.id.searchBox) .asInstanceOf[AutoCompleteTextView]
    • Mixin Inheritanceclass MainActivity extends MapActivity with Logging with DatabaseHelpers with MapHelpers
    • Collections● Best collection library I ever used ● Sorry google-collections...● Using arrays is easy● @specialized
    • Collection examplesval suggestions = areas map { _.name }val index = areas.indexWhere( _.name == searchString)val index = areas.indexWhere(_.contains(coordinate))pointList.minBy(_.lat)
    • First class functionsclass AreaOverlay( areas: Array[Area], selectListener: Int => Unit)new AreaOverlay( areas, this.onAreaSelected)
    • Convert listeners into functionsimplicit def fn2ClickListener( f: View => Unit): View.OnClickListener = new View.OnClickListener() { override def onClick(v: View) = f(view) }exitButton.setOnClickListener( this.onExitClick)
    • Files● Directory structure is not forced to mirror packages● Files can contain any amount of classes
    • Pattern matching● No NPEs when using Option[T]● Easy to work with data objects
    • Pattern matchinglastLocation match { case Some(c@Coordinate(lat, lon)) => ... case None => ...}
    • Implicitsimplicit def coordinate2geopoint( c: Coordinate): GeoPoint = new GeoPoint( c.lat * 1.0e6 toInt, c.lon * 1.0e6 toInt)
    • XMLfor (s <- xml "Document" "Style")placemarkElem "Polygon" "outerBoundaryIs" "LinearRing" "coordinates"
    • Bad stuff● Performance sensitive parts ● Learn to use “javap” ● Remove for-comprehensions and lambda functions ● Do not use boxed types “by accident”● Tools ● UI Editor ● Debugger ● Build time (dexing of scala library)
    • What I missed from Java● Google Guice● Maven● Good Eclipse integration● Feeling important...
    • Thank you!
    • Questions?