Download 03-intro-android - UTEP Computer Science

Introduction to Android
Chapter 1
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Objectives
• Understand what Android is
• Learn the differences between Java and Android
Java
• Examine the Android project structure
• Build a basic application using Android Studio
• Learn about the Model-View-Controller design
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Why Mobile Computing?
• Trends in computing industry
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Mainframe/batch
Workstation/client-server
PC/Web/P2P
Mobile?
• New Knowledge Areas (KA) in CS Curricula 2013
• Joint work by ACM and IEEE-CS
• Platform-based Development (PBD), e.g., mobile, web, and
game
• Good addition to your resume?
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Why Android?
• Android: Java-based, market dominance (87% share in 2016 Q3)
• IOS: Objective-C (13%)
Global smartphone OS market share in 2016 Q3 (from www.idc.com)
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What Is Android?
• Mobile OS by Google
• Based on Linux kernel
• Touchscreen devices
• Direct manipulation UI
• Touch gestures (swiping,
tapping, pinching)
• Virtual keyboard
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Evolution of Android
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Evolution of Android (Cont.)
Which version to
support?
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Android Programming Basics
• Java for most framework
• Java SDK + Android SDK + IDE (Android Studio or Eclipse)
• XML for configuration and resources
• Cursorless control (gestures using fingers)
• Framework concepts
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Activities
Intents
Views and widgets
Asynchronous calls
Background services
…
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Java vs. Android Java
• A large number of Java
libraries in the Android
platform
• Android SDK: Dalvik
compiler, debugger,
software libraries,
emulator
Jack on
Android Studio 2.1+
Java 8
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Java API vs. Android API
• No Java virtual machine in the Android platform
• Specialized VM, Dalvik and ART (v 5.0)
• Java bytecode compiled again into a proprietary
bytecode, dex bytecode
• Dex bytecode <-> Java bytecode
• Dex bytecode: compact Dalvik executable format
designed for Android systems, constrained in terms of
memory and processor speed.
• Dalvik dx tool for translating java bytecode into dex
bytecode
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Android Studio
• Official IDE for building Android applications,
including: Java editor, layout editor, Android SDK,
emulator, gradle, etc.
• Focuses exclusively on Android development and
comes bundled with the Android Software
Development Kit, SDK
• Android SDK, a set of tools and API libraries for:
• Building complete applications,
• Testing them on virtual devices, and
• Performing debugging and optimization
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Anatomy of Android Project
• Organization of Android project
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Source code
Application’s resources
Manifest settings
Build files
• All of these files eventually packaged into an apk
(distribution) file
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Android Manifest File
• An AndroidManifest.xml, is required for every
Android application.
• This file uses XML code to define specific
application information.
• This information can include general applicationwide settings such as the application’s style and
launch icon.
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AndroidManifest.xml
<manifest xmlns:android="..."
package="edu.utep.cs.cs4330.helloworld"
android:versionCode="1"
android:versionName="1.0">
<application
androd:icon="@drawable/launch_icon"
android:label="@string/app_name">
<activity android:name=".MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.categry.LAUNCHER"/>
</intent-filter>
</activity>
</application>
<uses-sdk android:minSdkVersion="17"/>
</manifest>
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Java Source Code
• The Java source code of an application is placed in
the java directory of the project structure.
• A main file, often named MainActivity, is a Java file
that is auto-generated when the project is first
created.
• Can include JUnit test files, local tests and
instrumented tests.
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Drawable/mipmap Resources
• The drawable folder is located in the res directory
• res contains the application resources
• Drawable resources are image files, such as
application icons, buttons, and background textures
• Q: mipmap vs. drawable folders?
• mipmap for app/launch icons
• drawable for all others
• Q: how to refer to an XML resource such as a
drawable in Java source code?
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Generalized Screen Size
• xlarge screens are at least 960dp x 720dp
• large screens are at least 640dp x 480dp
• normal screens are at least 470dp x 320dp
• small screens are at least 426dp x 320dp
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Layout XML Files
• User interface screens are visually designed and
coded as XML layout files.
• The design and arrangement of the elements on
the screen are implemented using XML code in a
layout file.
• Q: Advantages and disadvantages?
• Q: How to associate an XML layout with an activity?
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Example: activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
…>
<TextView … />
<LinearLayout …
android:orientation="horizontal">
<Button …
android:id="@+id/startButton"
android:text="@string/start"
android:onClick="startClicked" />
<Button … />
</LinearLayout>
</RelativeLayout>
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In-class: Timer App
To have a taste of Android programming by:
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Defining a simple UI in XML file (activity_main.xml),
Externalizing constants in XML file (strings.xml),
Associating UI with activity (setContentView),
Retrieving views defined in XML (findViewById),
Defining control code for views (android:onClick),
Separating model code from view and control.
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Model-View-Controller
• Android applications tend to rely on the ModelView-Controller design architecture.
• This architecture assigns one of three roles that
objects can play in an application.
View
(UI element)
update UI
notify user action
Control
update data
Model
(data)
notify change
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Sharing Android Apps
• Android requires the application to be digitally
signed with a certificate.
• Android uses this certificate to identify the author.
• Android apps typically use self-signed certificates,
in which the app developer holds the certificate’s
private key.
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