BlackBerry App Lifecycle Java ME API

BlackBerry App Lifecycle Java ME API

BlackBerry App Life Cycle • Application Starts • Three ways to start an app: • User clicks app icon • App starts automatically on startup or reboot • App is started by another app • Starting point in your application class is main() method Wendi Jollymore, ACES

BlackBerry App Life Cycle • Application Object Is Created • Triggered in the main() method • You instantiate your application class that extends UiApplication • Application classes with a Ui must extend UiApplication class • Can only have one UiApplication instance for any application • Otherwise RuntimeException is thrown. Wendi Jollymore, ACES

BlackBerry App Life Cycle • Event thread is started • main() is the main thread or process that’s running • Do anything you need to do here before you pass control to BB O/S • enterEventDispatcher() method call • Takes control of the main thread • Draws the main screen and listens for events • Won’t return, so if you need something else done in main(), do it first Wendi Jollymore, ACES

BlackBerry App Life Cycle • Events are processed • User events triggered by input from trackball, touch screen, keyboard, etc • Other events • Application Exits • When the last screen is removed from the stack. • Avoid System.exit() !! • Close all screens until the last screen is closed. • Proper clean up of all application state Wendi Jollymore, ACES

What is the API? • Application Program Interface • The collection and definition of building blocks available in a language • Descriptions of classes and their public methods • http://en.wikipedia.org/wiki/Api • Where to read the API docs? • http://www.blackberry.com/developers/docs/6.0.0api/index.html • Go to any JDE folder and select BlackBerry JDE API Reference Wendi Jollymore, ACES

Java ME API • Java ME – Micro Edition • For developing mobile apps • Runs on custom JVM for BlackBerry • BlackBerry Java Virtual Machine • MIDP 2.0 Standard– Mobile Information Device Profile • http://www.webopedia.com/TERM/M/MIDP.html • Part of Java ME API used for various mobile devices (not just for RIM) • Contains APIs for persistent storage, user interface, networking Wendi Jollymore, ACES

Java ME API • CLDC – Connected Limited Device Configuration • http://www.webopedia.com/TERM/C/CLDC.html • A specification for a stripped down virtual machine • For devices with very limited memory • Contains minimalist versions of java.lang, java.util, java.io • Contains java.microedition.io for network connections Wendi Jollymore, ACES

Java ME API • Other API Extensions specific to BlackBerry devices • User Interface • Persistent Data Storage • Networking • Event Listeners • Application Integration • Additional utilities for encryption, compression, location-based services, etc. Wendi Jollymore, ACES

Using API to Create App • Simplest: Start with two classes • An application class • The main application where it all starts • Extends UiApplication class • Three main tasks to perform: • Create an instance of the app • Create main screen and push onto display stack • Start the event dispatch thread Wendi Jollymore, ACES

Using API to Create App • Simplest: Start with two classes (continued) • A screen class • A visible display • Extends MainScreen class • Could have components, images, user input, etc • Components = Fields • net.rim.device.api.ui.Field • Layout = Managers • net.rim.device.api.ui.Manager Wendi Jollymore, ACES

UiApplication Class • net.rim.device.api.ui.UiApplication • Child of Application class • A non-gui program would extend this • Base class for all UI applications • Contains a screen stack • Only top screen is ever visible • pushScreen(screen) adds a screen to the stack • Lays out and prints the screen object • A screen can only be pushed onto the stack once, or exception occurs Wendi Jollymore, ACES

UiApplication Class public class MyApp extends UiApplication { public MyApp() { MyScreen scr = new MyScreen(); pushScreen(scr); } // ... } Wendi Jollymore, ACES

UiApplication Class • Event dispatcher thread • enterEventDispatcher() called on your application class • Takes control of main thread • Handles all drawing and event-handling • Never returns; ends when application ends • Call this in the application’s main() method Wendi Jollymore, ACES

UiApplication Class public class MyApp extends UiApplication { public MyApp() { MyScreen scr = new MyScreen(); pushScreen(scr); } public static void main(String[] args) { MyApp app = new MyApp(); app.enterEventDispatcher(); } } Wendi Jollymore, ACES

MainScreen Class • net.rim.device.api.ui.container. MainScreen • Child of Screen/FullScreen class • Has a VerticalFieldManager, title area, default menu, etc • In the MainScreen constructor is where you’d create and lay out your main UI Wendi Jollymore, ACES

MainScreen Class public class MyScreen extends MainScreen { public MyScreen() { LabelField label = new LabelField(“Hello!"); add(label); LabelField title = new LabelField("Java ME"); this.setTitle(title); } } Wendi Jollymore, ACES

Hierarchy • It’s interesting to note the inheritance hierarchy of these classes: Wendi Jollymore, ACES

Exercises and Homework • Exercise: • Do the exercise in the Lesson 2 notes • For next class: • Read Chapter 4 of Beginning BlackBerry Wendi Jollymore, ACES

BlackBerry App Lifecycle Java ME API