Android Deep Dive
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This document provides an overview and summary of the Android deep dive presentation given by Marko Gargenta at Sprint Dev Con 2010. It discusses the Android stack including the Linux kernel, native libraries like WebKit and SQLite, the Dalvik VM, and the application framework. It also covers building a basic "Hello World" Android app, common app components like activities, services, content providers and broadcasts receivers. The document summarizes the Android user interface approach using XML layouts and views, and operating system features such as security, files system, and cloud integration.
Android Deep Dive
- 1. Marko Gargenta Android Deep Dive Sprint Dev Con 2010
- 2. About Marko Gargenta Developed Android Bootcamp for Marakana. Taught over 1,000 developers on Android. Clients include Qualcomm, Sony-Ericsson, Motorola, Texas Instruments, Cisco, Sharp, DoD. Author of upcoming Learning Android by O’Reilly. Spoke at OSCON, ACM, IEEE, SDC. Organizes SFAndroid.org
- 3. Agenda • The Stack • Hello World! • Main Building Blocks • Android User Interface • OperaFng System Features • Debugging and Tools • Summary
- 5. The Stack
- 6. Linux Kernel Android runs on Linux. Linux provides: Hardware abstraction layer Memory management Process management Networking Users never see Linux sub system The adb shell command opens Linux shell Linux Kernel Libraries Application Framework Applications Home Contacts Phone Browser Other Activity Manager Window Manager Content Providers View System Package Manager Telephony Manager Resource Manager Location Manager Notiication Manager Surface Manager OpenGL SGL Media Framework FreeType SSL SQLite WebKit libc Android Runtime Core Libs Delvik VM Display Driver Keypad Driver Camera Driver WiFi Driver Flash Driver Audio Driver Binder Driver Power Mgmt
- 7. NaFve Libraries Pieces borrowed from other open source projects: Bionic, a super fast and small license-friendly libc library optimized for Android WebKit library for fast HTML rendering OpenGL for graphics Media codecs offer support for major audio/video codecs SQLite database Much more… Linux Kernel Libraries Application Framework Applications Home Contacts Phone Browser Other Activity Manager Window Manager Content Providers View System Package Manager Telephony Manager Resource Manager Location Manager Notiication Manager Surface Manager OpenGL SGL Media Framework FreeType SSL SQLite WebKit libc Android Runtime Core Libs Delvik VM Display Driver Keypad Driver Camera Driver WiFi Driver Flash Driver Audio Driver Binder Driver Power Mgmt
- 8. Dalvik Dalvik VM is Android implementation of Java VM Dalvik is optimized for mobile devices: • Battery consumption • CPU capabilities Key Dalvik differences: • Register-based versus stack-based VM • Dalvik runs .dex files • More efficient and compact implementation • Different set of Java libraries than JDK
- 9. ApplicaFon Framework The rich set of system services wrapped in an intuitive Java API. This ecosystem that developers can easily tap into is what makes writing apps for Android easy. Location, web, telephony, WiFi, Bluetooth, notifications, media, camera, just to name a few. Linux Kernel Libraries Application Framework Applications Home Contacts Phone Browser Other Activity Manager Window Manager Content Providers View System Package Manager Telephony Manager Resource Manager Location Manager Notiication Manager Surface Manager OpenGL SGL Media Framework FreeType SSL SQLite WebKit libc Android Runtime Core Libs Delvik VM Display Driver Keypad Driver Camera Driver WiFi Driver Flash Driver Audio Driver Binder Driver Power Mgmt
- 10. ApplicaFons Dalvik Executable + Resources = APK Must be signed (but debug key is okay for development) Many markets with different policies
- 11. Android and Java Android Java = Java SE – AWT/Swing + Android API
- 12. Android SDK -‐ What’s In The Box SDK Tools Docs Platforms Data Skins Images Samples Add-ons Google
- 13. HELLO WORLD!
- 14. 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 AcFvity Java class
- 15. Anatomy of An App Java Code + XML and Other Resources + Manifest File = Android App
- 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); } }
- 19. Running on Emulator Emulator, not a simulator
- 21. AcFviFes Android Application Main Activity Another Activity Another Activity An Activity represents a screen or a window. Sort of.
- 22. AcFvity Lifecycle Starting Running PausedStopped Destroyed (1) onSaveInstanceState() (2) onPause() (3) onResume() (2) onStart() (1) onRestart() onResume() (1) onSaveInstanceState() (2) onStop() <process killed> onDestroy() or <process killed> (1) onCreate() (2) onStart() (3) onRestoreInstanceState() (4) onResume() Activities have a well- defined lifecycle. The Android OS manages your activity by changing its state. You fill in the blanks.
- 23. Intents Android Application Another Activity Android Application Main Activity Intent Intent Main Activity Intent Another Activity Intents represent events or actions. They are to Android apps what hyperlinks are to websites. Sort of. Intents can be implicit or explicit.
- 24. Services Services are code that runs in the background. They can be started and stopped. Services doesn’t have UI.
- 25. Service Lifecycle Service also has a lifecycle, but it’s much simpler than activity’s. An activity typically starts and stops a service to do some work for it in the background, such as play music, check for new tweets, etc. Services can be bound or unbound.
- 26. Content Providers Content Provider Content URI insert() update() delete() query() Content Providers share content with applications across application boundaries. Examples of built-in Content Providers are: Contacts, MediaStore, Settings and more.
- 27. Broadcast Receivers An Intent-based publish-subscribe mechanism. Great for listening system events such as SMS messages.
- 28. Twitter.com MyTwitter Activity Updater Service Timeline Receiver Timeline DB Prefs XML Updates Status via web service Preference Activity Pull timeline updates via web service Insert updates in DB Notify of new status Timeline Activity Pull timeline from DB Update list Timeline Adapter Update ListView Read/write preferences Boot Receiver Start at boot Read Prefs Read Prefs Yamba – A Real World App
- 30. Two UI Approaches Procedural DeclaraCve You write Java code Similar to Swing or AWT You write XML code Similar to HTML of a web page You can mix and match both styles. Best practice: • Start with XML and declare most of UI • Switch to Java and implement the UI logic
- 31. XML-‐Based User Interface Use WYSIWYG tools to build powerful XML-based UI. Easily customize it from Java. Separate concerns.
- 32. Common View ProperFes Layout Width FILL_PARENT, WRAP_CONTENT or a specific size in units. Layout Height FILL_PARENT, WRAP_CONTENT or a specific size in units. Layout Weight How greedy or generous a widget is. Value is 0 to 1. Layout Gravity How to align widget within parent Gravity How to align content of widget within itself Id Unique id of this widget, usually @+id/someUniqueId! Text Text for the content of the component, usually @string/myText!
- 33. 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
- 34. Views and Layouts Layouts contain widgets and other layouts forming a “composite” pattern.
- 35. Linear Layout One of the most commonly used layouts. It lays its children next to each other, either horizontally or vertically.
- 36. RelaFve Layout Children of relative layout are placed in relationship to each other. This layout is efficient.
- 37. Table Layout Table layout puts its children into table rows and columns. It is similar to an HTML table.
- 38. Frame Layout Frame layout places its children on top of each other, like a deck of cards. It is useful for widgets such as tabs or as a placeholder for views added programmatically.
- 39. Common UI Components Android UI includes many common modern UI widgets, such as Buttons, Tabs, Progress Bars, Date and Time Pickers, etc.
- 40. SelecFon Components Some UI widgets may be linked to zillion pieces of data. Examples are ListView and Spinners (pull-downs).
- 41. Adapters 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. Data Source Adapter
- 42. 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.
- 44. Graphics & AnimaFon Android has rich support for 2D graphics. You can draw & animate from XML. You can use OpenGL for 3D graphics.
- 45. MulFmedia 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();
- 47. Security Android Application Prefs DB File System Linux Process Each Android application runs inside its own Linux process. Additionally, each application has its own sandbox file system with its own set of preferences and its own database. Other applications cannot access any of its data, unless it is explicitly shared.
- 48. File System The file system has three main mount points. One for system, one for the apps, and one for whatever. Each app has its own sandbox easily accessible to it. No one else can access its data. The sandbox is in /data/data/com.marakana/ SDCard is expected to always be there. It’s a good place for large files, such as movies and music. Everyone can access it.
- 49. Cloud to Device Push Big deal for many pull-based apps. Will make devices use less battery.
- 50. Preferences Your app can support complex preferences quite easily. You define your preferences in an XML file and the corresponding UI and data storage is done for free.
- 51. SQLite Database Android ships with SQLite3 SQLite is a • Zero configuration • Serverless • Single database file • Cross-Platform • Compact • Public Domain Database engine. May you do good and not evil May you find forgiveness for yourself and forgive others May you share freely, never taking more than you give.
- 52. DEBUGGING ANDROID APPS
- 53. 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.
- 54. Debugger Your standard debugger is included in SDK, with all the usual bells & whistles.
- 55. 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.
- 56. 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.
- 57. Summary Android is open and complete system for mobile development. It is based on Java and augmented with XML. Android is being adopted very quickly both by users, carriers, and manufacturers. It takes about 3-5 days of intensive training to learn Android application development for someone who has basic Java (or similar) experience. Licensed under Creative Commons License (cc-by-nc-nd) – non-commercial. Please Share! Marko Gargenta, Marakana.com marko@marakana.com +1-415-647-7000