Java & Android. Java Fundamentals. Madis Pink 2016 Tartu

Transcription

1 Java & Android Java Fundamentals Madis Pink 2016 Tartu 1

2 Agenda» Brief background intro to Android» Android app basics:» Activities & Intents» Resources» GUI» Tools 2

3 Android» A Linux-based Operating System» Announced by Google & the Open Handset Alliance Nov 2007» First device with Android 1.0 shipped in

4 Android» The primary language for writing apps is actually Java» The standard library is mainly Java 6 with a lot of Android-specific classes on top» There are 25 API versions, most apps target Android 4.4 (API 19) or higher today 4

5 VMs on Android» Dalvik - all Android versions up to 4.4, just-intime compilation added in Android version 2.2» ART - New runtime with ahead-of-time compilation, shipped with Android 5.0 and later» Both operate on DEX (Dalvik EXecutable) bytecode 5

6 Dex Bytecode» Design goals» Compilation target for.java sources» Code size» Interpreting performance» Bytecode instructions operate on registers» Many classes in a single.dex file 6

7 Dex Toolchain(s)» Dexer (dx) - transforms Java 7 bytecode (.class) to dex» Jack & Jill - Experimental direct Java compilation to dex, supports Java 8 7

8 Dex & Dalvik Example class Hello { public static void main(string[] args) { System.out.println("Hello world!"); } } 8

9 Dex & Dalvik Example $ javac Hello.java -target 1.7 -source 1.7 $ java Hello Hello world! 9

10 Dex & Dalvik Example $ javac Hello.java -target 1.7 -source 1.7 $ java Hello Hello world! $ dx --dex --output=out.dex Hello.class 10

11 Dex & Dalvik Example $ javac Hello.java -target 1.7 -source 1.7 $ java Hello Hello world! $ dx --dex --output=out.dex Hello.class $ adb push out.dex /data/local/tmp/out.dex 11

12 Dex & Dalvik Example $ javac Hello.java -target 1.7 -source 1.7 $ java Hello Hello world! $ dx --dex --output=out.dex Hello.class $ adb push out.dex /data/local/tmp/out.dex $ adb shell dalvikvm -cp /data/local/tmp/out.dex Hello Hello world! 12

13 Anatomy of an App Each app is an.apk file - a zip in disguise - with the following contents:» AndroidManifest.xml - the manifest, describes the app» classes.dex - the dex bytecode» resources.arsc - compiled Android resources» res/* - compiled layouts, PNG bitmaps, etc» assets/* - blob assets: databases, audio files, etc 13

14 Anatomy of an App» No main(string[])» Components as entry points:» Activities» Services» Broadcast receivers» Content Providers» These are defined in the AndroidManifest.xml 14

15 Android Projects» Built with Gradle!» src/main/java - Java sources» src/main/res - Android resources» src/main/androidmanifest.xml - the manifest» build.gradle - Gradle build file, describes how to build the app 15

16 Intermission all samples at 16

17 Activities 17

18 Activity» class * extends android.app.activity» Started with an Intent - a user action» Represents a screen in an application» Owns a View hierarchy (GUI objects)» Handles user input events» Instantiated by the framework» Lifecycle controlled by the framework 18

19 Activities Example - App» InboxActivity - lists all s in Inbox» View Activity - view a single » ComposeActivity - compose/send a new » LoginActivity - log the user in 19

20 Activity Lifecycle» Driven by the framework through calls to specific Activity methods» oncreate/ondestroy - activity created» onstart/onstop - activity visible» onresume/onpause - activity is "on top"» When overriding any of these, make sure to call to super! 20

21 Starting an Activity - Intents» All Activities are started by defining an Intent - an object that represents user's intentions» Sort of like a request that apps can respond to» Requires a Context instance to send the Intent to the OS» All components, including activities extend Context» Two kinds of intents - explicit and implicit 21

22 Explicit Intents public void clickhelp() { // launch HelpActivity of this app Intent i = new Intent(context, HelpActivity.class); context.startactivity(i); }» Used to launch a specific activity on the device, usually within the same app 22

23 Implicit Intents public void sendfeedback() { Uri uri = Uri.parse("mailto:jf@zeroturnaround.com"); Intent i = new Intent(Intent.ACTION_SENDTO, uri); startactivity(i); }» Used for general actions like Send , Open a webpage, Take a picture etc 23

24 Implicit Intents 24

25 Implicit Intents public void openwebpage() { Uri uri = Uri.parse(" Intent i = new Intent(Intent.ACTION_VIEW, uri); startactivity(i); } 25

26 Implicit Intents 26

27 Defining an Activity package org.zeroturnaround.jf.android; import android.app.activity; public class HelloActivity extends Activity { } 27

28 Defining an Activity package org.zeroturnaround.jf.android; import android.app.activity; import android.os.bundle; import android.widget.toast; public class HelloActivity extends Activity { protected void oncreate(bundle savedinstancestate) { // always need to call super super.oncreate(savedinstancestate); // display our message String msg = "Hello World!"; Toast.makeText(this, msg, Toast.LENGTH_SHORT).show(); } } 28

29 AndroidManifest.xml <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.helloactivity"> <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> </intent-filter> </activity> </application> </manifest> 29

30 AndroidManifest.xml The <manifest /> tag tells us that this is an app with the application ID org.zeroturnaround.jf.android <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application> <!-- components go here --> </application> </manifest> 30

31 AndroidManifest.xml The <activity /> tag declares an Activity component with the classname org.zeroturnaround.jf.android.helloactivity <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.helloactivity"> <!-- optional intent filter goes here --> </activity> </application> </manifest> 31

32 AndroidManifest.xml The <intent-filter /> tag declares which implicit Intents our Activity handles, in this case it is the MAIN action under the LAUNCHER category This makes our app visible in the Launcher app <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> </intent-filter> 32

33 AndroidManifest.xml <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.helloactivity"> <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> </intent-filter> </activity> </application> </manifest> 33

34 34

35 More Information Activities: components/activities.html Intents: components/intents-filters.html Manifest: manifest/manifest-intro.html 35

36 Resources 36

37 37

38 Resources» Placed in src/main/res folder» Precompiled by aapt during the Gradle build» Value resources - strings, floats, integers, booleans,...» Complex resources - arrays, plurals,...» File resources - bitmaps, XMLs, drawables, layouts,... 38

39 Value Resources <?xml version="1.0" encoding="utf-8"?> <resources> <string name="app_name">hello</string> <string name="hello_world">hello World!</string> </resources>» Placed in src/main/res/values/<filename>.xml, where <FILENAME> can be anything, like strings.xml 39

40 Drawables» Placed in src/main/res/drawable» Can be XML (describing shapes, colours, gradients) or bitmaps» Automatically scaled by the OS 40

41 Layouts» Placed in src/main/res/layout» XML files for describing UI» More on these later :) 41

42 Accessing Resources from XML» Resources can be referenced in XML resources (including the manifest) <identifier>» A 42

43 Accessing Resources from Code» All resources get a runtime integer ID, placed in a class called R» Need to dereference through a Resources instance, obtained through a Context» Example dereferences:» getresources().getstring(r.string.app_name)» getresources().getdrawable(r.drawable.ic_launcher) 43

44 Resource Qualifiers» Resource folders can have extra qualifiers with -suffixes» values-et containing Estonian strings» Framework decides at runtime which resource to use» Also used to have custom layouts for tablets, different drawables for device densities, etc 44

45 Resource Qualifiers Resource qualifier examples:» res/layout-land for landscape layouts» res/drawable-xhdpi, res/drawable-hdpi, res/ drawable-mdpi for icons at various resolutions» res/values-et, res/values-ru for localization 45

46 Resources <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application> <!-- components go here --> </application> </manifest> 46

47 Resources <manifest xmlns:android=" package="org.zeroturnaround.jf.android" > <application android:label="hello World"> <!-- components go here --> </application> </manifest> 47

48 Resources <?xml version="1.0" encoding="utf-8"?> <resources> <string name="app_name">hello</string> <string name="hello_world">hello World!</string> </resources> 48

49 Resources <application android:label="hello World"> 49

50 Resources <application 50

51 Resources <application 51

52 Resources // display our message String msg = "Hello World!"; Toast.makeText(this, msg, Toast.LENGTH_SHORT).show(); 52

53 Resources // display our message String msg = getresources().getstring(r.string.hello_world); Toast.makeText(this, msg, Toast.LENGTH_SHORT).show(); 53

54 Resources 54

55 More Information Resources overview - guide/topics/resources/overview.html 55

56 GUI 56

57 GUI - Units» No absolute coordinates!» Units:» dip (dp) - density-independent pixels» sp - scaled pixels, scale with the text size» px - actual physical pixels» Even with dp the sizes of screens vary wildly 57

58 View Hierarchy» ViewGroup (container/node) and View (leaf node)» View groups lay out their children, which could be nested groups» Can be declared through code» Can be inflated from XML layouts» Use setcontentview(view root) or setcontentview(int layoutresid) to attach a hierarchy to an Activity 58

59 Views» TextView - displays text» ImageView - displays images» EditText - text input» Button - clickable TextView with various states 59

60 ViewGroups» FrameLayout - simple layouts for framing children» LinearLayout - lays views out in a single row/ column» RelativeLayout - lays views out in relation to each other with rules» ListView - scrolling a lot of similar views with caching 60

61 Views protected void oncreate(bundle savedinstancestate) { // always need to call super super.oncreate(savedinstancestate); // display our message String msg = getresources().getstring(r.string.hello_world); Toast.makeText(this, msg, Toast.LENGTH_SHORT).show(); } 61

62 Views Replace our toast with a TextView // display our message String msg = "Hello World!"; TextView root = new TextView(this); root.settext(msg); setcontentview(root); 62

63 Views src/main/res/layout/hello.xml: <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android=" android:layout_width="match_parent" android:layout_height="match_parent" /> 63

64 Views src/main/res/layout/hello.xml: <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android=" android:layout_width="match_parent" android:layout_height="match_parent" />... and in our HelloActivity.onCreate: setcontentview(r.layout.hello); 64

65 Views 65

66 Views Add some padding with android:padding <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android=" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp" /> 66

67 Views Make the font larger with android:textsize <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android=" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp" android:textsize="32sp" /> 67

68 Views 68

69 Handling Events» Views can be given generated IDs via This will generate a unique integer accessible via R.id.someIdentifier» Use findviewbyid(int id) to find the view in code» Note! Always returns View so might need to cast 69

70 Handling Events Adding a button to our view <Button android:id="@+id/my_button" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/click" /> 70

71 Handling Events Adding a button to our view <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android=" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp" android:orientation="vertical"> <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" android:textsize="32sp" /> <Button android:id="@+id/my_button" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/click" /> </LinearLayout> 71

72 Handling Events We can use setonclicklistener to attach a handler to the click event setcontentview(r.layout.hello); // attach an OnClickListener to the view with id `my_button` Button mybutton = (Button) findviewbyid(r.id.my_button); mybutton.setonclicklistener(new View.OnClickListener() public void onclick(view v) { Toast.makeText(v.getContext(), R.string.click, Toast.LENGTH_SHORT).show(); } }); 72

73 Handling Events 73

74 More information Layouts: declaring-layout.html Handling events: topics/ui/ui-events.html 74

75 Tools 75

76 Android Studio in 5 minutes» The official IDE for Android development» Based on IntelliJ IDEA Community Edition» Download: index.html» Before opening any project, open Configure -> SDK Manager to download necessary SDK components for the homework 76

77 Android Studio - Configuring SDK Under the SDK Platforms tab, click Show Package Details and make sure the following items are checked in the Android 7.0 (Nougat) category:» Android SDK Platform 24» Sources for Android 24» Google APIs Intel x86 Atom System Image 77

78 Android Studio - Configuring SDK Under the SDK Tools tab, click Show Package Details and make sure the following items are checked:» under Android SDK Build-Tools» Android SDK Platform-Tools » Android SDK Tools » Intel x86 Emulator Accelerator (HAXM installer) 78

79 Android Studio - Configuring SDK With that being done, press Apply, read through and Accept both Android SDK license and Intel licenses and press Next to install the components 79

80 Android Studio in 5 minutes» Import the homework/samples folder via Open an existing Android Studio project» Find the green ' ' next to a dropdown in the toolbar» Studio will ask you to create an emulator, any emulator with the version later than (API 15) will do» Note: we've already downloaded the image for Nougat 7.0» You should see the app on the emulator \o/ 80

81 Developing with a Device» Settings -> About phone» Scroll down & tap Build number 7 times» You are now a developer!» Settings -> Developer options» Make sure USB Debugging is enabled 81

82 Gradle» Project layout similar to Maven» Instead of XML the build is defined through a Groovy DSL» No installation needed, gradlew will download Gradle for you» gradlew build - builds the project 82

83 More Information Android Studio - index.html Android and Android Studio: Getting Started (~10min video)

84 Homework 14 84

85 Homework 14 All the details are at: Due :59:59 Estonian time Do not leave this for the last minute! Help/questions: 85

86 Links Samples - Activities - Intents - Manifest - Resources overview - Layouts - Handling events - Android Studio - Android and Android Studio: Getting Started (~10min video)