Android: A 9,000-foot Overview
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This document provides an overview of Android and its development environment. It discusses Android's history and key components such as the stack, SDK, activities, intents, services, and user interface. It also covers debugging tools and provides a high-level summary of Android as a Java-based platform where developers write Java code and XML layouts to build applications.
Android: A 9,000-foot Overview
- 1. Android: A 9,000-‐foot Overview Marko Gargenta Marakana
- 2. Agenda • Android History • Android and Java • The Stack • Android SDK • Hello World! • Main Building Blocks • Android User Interface • Debugging • Summary
- 3. History 2005 Google buys Android, Inc. Work on Dalvik starts 2007 OHA Announced Early SDK 2008 G1 Announced SDK 1.0 Released 2009 G2 Released Cupcake, Donut, Eclair
- 4. Android and Java Android Java = Java SE – AWT/Swing + Android API
- 6. The Stack
- 7. Linux Kernel Android runs on Linux. Applications Home Contacts Phone Browser Other Linux provides as well as: Hardware abstraction layer Application Framework Memory management Activity Window Content View Process management Manager Manager Providers System Package Telephony Resource Location Notiication Networking Manager Manager Manager Manager Manager Libraries Users never see Linux sub system Surface Media SQLite Android Runtime Manager Framework Core Libs The adb shell command opens OpenGL FreeType WebKit Delvik Linux shell SGL SSL libc VM Display Camera Linux Kernel Flash Binder Driver Driver Driver Driver Keypad WiFi Audio Power Driver Driver Driver Mgmt
- 8. NaXve Libraries Bionic, a super fast and small Applications GPL-based libc library optimized Home Contacts Phone Browser Other for embedded use Application Framework Surface Manager for composing Activity Window Content View window manager with off-screen Manager Manager Providers System buffering Package Telephony Resource Location Notiication Manager Manager Manager Manager Manager Libraries 2D and 3D graphics hardware Surface Media SQLite Android Runtime support or software simulation Manager Framework Core Libs OpenGL FreeType WebKit Delvik Media codecs offer support for SGL SSL libc VM major audio/video codecs Display Camera Linux Kernel Flash Binder Driver Driver SQLite database Driver Driver Keypad WiFi Audio Power Driver Driver Driver Mgmt WebKit library for fast HTML rendering
- 9. Dalvik Dalvik VM is Google’s implementation of Java Optimized for mobile devices Key Dalvik differences: Register-based versus stack-based VM Dalvik runs .dex files More efficient and compact implementation Different set of Java libraries than SDK
- 10. ApplicaXon Framework Activation manager controls the life Applications cycle of the app Home Contacts Phone Browser Other Content providers encapsulate data Application Framework that is shared (e.g. contacts) Activity Window Content View Manager Manager Providers System Package Telephony Resource Location Notiication Resource manager manages Manager Manager Manager Manager Manager everything that is not the code Libraries Surface Media SQLite Android Runtime Manager Framework Location manager figures out the Core Libs location of the phone (GPS, GSM, OpenGL FreeType WebKit Delvik WiFi) SGL SSL libc VM Notification manager for events Display Driver Camera Driver Linux Kernel Flash Driver Binder Driver such as arriving messages, Keypad WiFi Audio Driver Power Mgmt Driver Driver appointments, etc
- 11. ApplicaXons
- 12. Android SDK -‐ What’s in the box SDK Tools Docs Platforms Data Skins Images Samples Add-ons Google Maps
- 13. The Tools Tools are important part of the SDK. They are available via Eclipse plugin as well as command line shell.
- 14. HELLO WORLD!
- 15. Create New Project Use the Eclipse tool to create a new Android project. Here are some key constructs: Project Eclipse construct Target minimum to run App name whatever Package Java package AcXvity Java class
- 16. The Manifest File <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.marakana" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".HelloAndroid" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="5" /> </manifest>
- 17. The Layout Resource <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> </LinearLayout>
- 18. The Java File package com.marakana; import android.app.Activity; import android.os.Bundle; public class HelloAndroid extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } }
- 21. AcXviXes Activity is to an Android Application application what a Main Activity Another Another Activity Activity web page is to a website. Sort of.
- 22. AcXvity Lifecycle Starting Activities have a well- (1) onCreate() (2) onStart() (3) onRestoreInstanceState() defined lifecycle. The (4) onResume() Android OS manages your activity by Running changing its state. (3) onResume() (2) onStart() (1) onSaveInstanceState() (2) onPause() You fill in the blanks. (1) onRestart() onResume() (1) onSaveInstanceState() Stopped (2) onStop() Paused onDestroy() or <process killed> <process killed> Destroyed
- 23. Intents Intents are to Android Application Android apps Another Main Activity Intent what hyperlinks Activity are to websites. They can be Intent implicit and Android Application explicit. Sort of like absolute and Main Activity Intent Another Activity relative links.
- 24. Services A service is something that can be started and stopped. It doesn’t have UI. It is typically managed by an activity. Music player, for example
- 25. Service Lifecycle Service also has a Starting lifecycle, but it’s (1) onCreate() much simpler than (2) onStart() activity’s. An activity onStart() typically starts and stops a service to do Stopped Running some work for it in the background. onStop() Such as play music, check for new onDestroy() or tweets, etc. <process killed> Destroyed
- 26. Content Providers Content Providers share Content content with applications Provider across application Content URI boundaries. insert() Examples of built-in update() Content Providers are: delete() Contacts, MediaStore, query() Settings and more.
- 27. Broadcast Receivers An Intent-based publish-subscribe mechanism. Great for listening system events such as SMS messages.
- 29. Two UI Approaches Procedural Declara?ve You write Java code You write XML code Similar to Swing or AWT Similar to HTML of a web page You can mix and match both styles. Declarative is preferred: easier and more tools
- 30. XML-‐Based User Interface Use WYSIWYG tools to build powerful XML-based UI. Easily customize it from Java. Separate concerns.
- 31. Dips and Sps px (pixel) Dots on the screen in (inches) Size as measured by a ruler mm (millimeters) Size as measured by a ruler pt (points) 1/72 of an inch dp (density-‐independent pixel) Abstract unit. On screen with 160dpi, 1dp=1px dip synonym for dp and oeen used by Google sp Similar to dp but also scaled by users font size preference
- 32. Views and Layouts ViewGroup ViewGroup View View View View ViewGroups contain other Views but are also Views themselves.
- 33. Common UI Components Android UI includes many common modern UI widgets, such as Buttons, Tabs, Progress Bars, Date and Time Pickers, etc.
- 34. SelecXon Components Some UI widgets may be linked to zillions of pieces of data. Examples are ListView and Spinners (pull-downs).
- 35. Adapters Adapter Data Source To make sure they run smoothly, Android uses Adapters to connect them to their data sources. A typical data source is an Array or a Database.
- 36. Complex Components Certain high-level components are simply available just like Views. Adding a Map or a Video to your application is almost like adding a Button or a piece of text.
- 38. Graphics & AnimaXon Android has rich support for 2D graphics. You can draw & animate from XML. You can use OpenGL for 3D graphics.
- 39. MulXmedia AudioPlayer lets you simply specify the audio resource and play it. VideoView is a View that you can drop anywhere in your activity, point to a video file and play it. XML: <VideoView android:id="@+id/video" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_gravity="center” /> Java: player = (VideoView) findViewById(R.id.video); player.setVideoPath("/sdcard/samplevideo.3gp"); player.start();
- 40. Google Maps Google Maps is an add-on in Android. It is not part of open-source project. However, adding Maps is relatively easy using MapView. XML: <com.google.android.maps.MapView android:id="@+id/map" android:clickable="true" android:layout_width="fill_parent" android:layout_height="fill_parent" android:apiKey="0EfLSgdSCWIN…A" />
- 41. DEBUGGING ANDROID APPS
- 42. LogCat The universal, most versatile way to track what is going on in your app. Can be viewed via command line or Eclipse. Logs can be generated both from SDK Java code, or low-level C code via Bionic libc extension.
- 43. Debugger Your standard debugger is included in SDK, with all the usual bells & whistles.
- 44. TraceView TraceView helps you profile you application and find bottlenecks. It shows execution of various calls through the entire stack. You can zoom into specific calls.
- 45. Hierarchy Viewer Hierarchy Viewer helps you analyze your User Interface. Base UI tends to be the most “expensive” part of your application, this tool is very useful.
- 46. Summary Android is based on Java. You write Java code, but technically don’t run it. Java is augmented with XML, mostly for UI purposes. Android Java is mostly based on Java SE with replacement UI libraries. Marko Gargenta, Marakana.com marko@marakana.com +1-415-647-7000 Licensed under Creative Commons License (cc-by-nc-nd). Please Share!