The document discusses mobile development using Scala on Android, highlighting the advantages of closures, strongly typed handlers, and lexical scoping. It provides code examples for creating basic event handlers in Scala, Objective-C, and Java, emphasizing the simplicity and correctness of Scala for Android development. Additionally, it touches on challenges faced with a large number of classes in mobile applications.

1. Scala on Your Phone:
Making Mobile
Development Suck Less
Michael Galpin, eBay
@michaelg

2. Example: Event Handlers

3. Just a Click

4. iPhone

6. Android

8. Objective-C

9. @synthesize textInput;
@synthesize label;
@synthesize name;
- (IBAction)changeGreeting:(id)sender {
self.name = textInput.text;
NSString *nameString = name;
if([nameString length] == 0) {
nameString = @"Code Camp";
}
NSString *greeting = [[NSString alloc]
initWithFormat:@"Hello %@!", nameString];
label.text = greeting;
[greeting release];
}
- (BOOL)textFieldShouldReturn:(UITextField *)theTextField {
if(theTextField == textInput) {
[textInput resignFirstResponder];
}
return YES;
}
- (void)dealloc {
[textInput release];
[label release];
[name release];
[super dealloc];
}

11. Java

12. @Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button sayButton = (Button) findViewById(R.id.say_button);
sayButton.setOnClickListener(new OnClickListener(){
public void onClick(View v) {
EditText nameBox = (EditText) findViewById(R.id.name);
String name = nameBox.getText().toString();
TextView greeting = (TextView) findViewById(R.id.greeting);
greeting.setText("Hello " + name);
}
});
}

13. Scala

14. override def onCreate(savedInstanceState:Bundle){
import R.id._
super.onCreate(savedInstanceState)
setContentView(R.layout.main)
val sayButton = findViewById(say_button).asInstanceOf[Button]
sayButton.setOnClickListener( () => {
val user = findViewById(name).asInstanceOf[EditText].text
findViewById(greeting).asInstanceOf[TextView].text = "Hello " + user
})
}

15. Advantages

16. Closures
• Strongly typed handlers • Forget one-method
interfaces
• Lexical scoping

17. Closures
• Strongly typed handlers • Forget one-method
interfaces
• Lexical scoping
val computedValue = parseInt(findViewById(foo).asInstanceOf[EditText].text)
this.post( () => {
val url = new URL("http://foo.com?qs=" + computedValue)
Source.fromStream(url.openStream).getLines.foreach(findViewById(results).text += _)
})
mainMenu.onClick = (item:MenuItem) => { startActivity(item.activity) }

18. Getters, Setters, Updates
mapImage.alpha = if (topLevelGroup.searchButton.clickable) BLENDED else OPAQUE
allTiles(selectedTileIndex) = throbberImageView

19. Operators
resultsLabelView += "Read more..."
keywordInput -= eventListener
mainMenu ++ fileMenuItems

20. Traits
class SearchDetailsActivity extends Activty with JsonParser, Trackable

21. XML
val results = for (suggested <- responseXml"Suggested"){
yield Term(sugested"Term" text, suggested"Priority" text)
}
nextNode match {
case <code>{txt}</code> => this.status = parseInt(txt)
case <state>{txt}</state> => this.state = txt
case _ =>
}

22. Trade Secrets

23. * Compiler Dex Compiler Compress
Source Code Class files Dex File APK

24. Implicits
object Activity{
implicit def funcToClicker1(f:_root_.android.view.View => Unit):OnClickListener =
new OnClickListener(){ def onClick(v:_root_.android.view.View)=f.apply(v)}
implicit def funcToClicker0(f:() => Unit):OnClickListener =
new OnClickListener() { def onClick(v:_root_.android.view.View)=f.apply}
implicit def funcToLongClicker0(f:() => Boolean):OnLongClickListener =
new OnLongClickListener() { def onLongClick(v:_root_.android.view.View) = f.apply}
implicit def funcToLongClicker1(f:_root_.android.view.View => Boolean):OnLongClickListener =
new OnLongClickListener() { def onLongClick(v:_root_.android.view.View) = f.apply(v)}
implicit def viewToRichView(v:_root_.android.view.View):scala.android.view.View = new
scala.android.view.View(v)
implicit def richViewToView(view:scala.android.view.View):_root_.android.view.View = view.base
}

25. Bag o’ Tricks
class ViewGroup(base:_root_.android.view.ViewGroup) extends View(base){
object views{
def +=(v:_root_.android.view.View){
base.addView(v)
}
def apply(index:Int) = new {
def update(v:_root_.android.view.View) = base.addView(index,v)
}
}
...
}

26. Bag o’ Tricks
class ViewGroup(base:_root_.android.view.ViewGroup) extends View(base){
object views{
def +=(v:_root_.android.view.View){
base.addView(v)
}
def apply(index:Int) = new {
def update(v:_root_.android.view.View) = base.addView(index,v)
}
}
...
}
myGroup.views += someOtherView
myGroup.views(3) = yetAnotherView

27. Scala on Android
• More Correct
• More Concise
• Simpler
• Perfect Fit

28. Challenges

29. 2500+ Classes

33. Hey, What About?