Android Application Development

Transcription

1 Android Application Development Octav Chipara

2 What is Android A free, open source mobile platform A Linux-based, multiprocess, multithreaded OS Android is not a device or a product It s not even limited to phones - you could build a DVR, a handheld GPS, an MP3 player, etc. 2

3 The Android stack 3

4 Android Application Framework 4

5 Android runtime Every Android app runs its own process, with its own instance of the Dalvik virtual machine Dalvik has been written so that it can run multiple VMs efficiently Dalvik VM executes files in Dalvik Executable (.dex) format more details in later lectures 5

6 Basic Android application components 6

7 Hello World

8 Application directory structure Directory src/ res/layout res/values res/drawable-?dpi/ AndroidManifest.xml gen/ Description source files contains the XML file the specifies constants, the etc. screen layout pictures used by the app the properties of the project automatically generated code 8

9 Generating GUIs Two ways to create GUIs in XML - a declarative approach in code - discouraged! A lot of the GUI-related files will be located in res/layout res/values res/androidmanifest.xml - key file in your development Referencing resources 9

10 Views and View Groups Views are the building blocks TextView, EditText, or ListView,... View Groups - define how the child views are laid out grid, lists 10

11 Properties of views and view components Three files you will be working on activity_main.xml, values.xml, and R.java you edit the xml files, R.java is automatically generated but used in your code <LinearLayout xmlns:android=" xmlns:tools=" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal" > <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight = "1" /> <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onclick="clickme" android:text="@string/button_label" /> </LinearLayout> res/layout /activity_main.xml 11

12 Properties of views and view components <resources> <string name="app_name">myfirstapp</string> <string name="hello_world">hello world! This is a new string! </string> <string name="menu_settings">settings</string> <string name="title_activity_main">mainactivity</string> <string name="button_label">send!</string> <string name="title_activity_display">displayactivity</string> </resources> res/values /strings.xml 12

13 Properties of views and view components public final class R { }... public static final class id { } public static final int LinearLayout1=0x7f070001; public static final int button1=0x7f070003; public static final int edittext1=0x7f070002; public static final int menu_settings=0x7f070004; public static final int textview=0x7f070000; public static final class layout { public static final int activity_display=0x7f030000; } public static final int activity_main=0x7f030001; public static final class menu { public static final int activity_display=0x7f060000; } public static final int activity_main=0x7f060001; public static final class string {... } res/gen/r.java 13

14 Properties of views and view components You can reference values between the files various files resources are defined in both the layout and values files resources are references to defined new resources 14

15 Layout Controls how Views are laid out FrameLayout : each child a layer LinearLayout : single row or column RelativeLayout : relative to other Views TableLayout : rows and columns AbsoluteLayout : <x,y> coordinates 15

16 Layouts are resizable 16

17 Layout parameters Specify many aspects of what s being rendered Examples: android:layout_height android:layout_width Tip: start with documentation for a specific View or Layout and then look at what s inherited from parent class 17

18 Activities Typically correspond to one screen in a UI if a UI is defined, then it has its own xml file under layouts however, they can be faceless be in a floating window return a value 18

19 Lifecycle of an Activity transient The KEY to a happy life with Android! 19

20 Static application states Resumed (aka running) activity is in foreground and user may interact with it Paused activity is partly obscured by another activity does not receive any user input Stopped (aka background) activity is not visible on the screen 20

21 What should go in each function call? protected void oncreate (Bundle savedinstancestate) here you can add different UI elements instantiate class-wide variables saveinstancestate - used to recreate an activity after it is destroyed 21

22 What should go in each function call? protected void onpause () on pause can be both an indication of user briefly switched to a different activity OR user switched apps you may want to suspend some actions of your activity e.g., playback audio or video release system resources e.g., camera or gps guidelines: you should avoid delay intensive operations (this should go onstop()) e.g., writing to files protected void onresume () (re) acquire the necessary to run the application e.g., cameras 22

23 What should go in each function call? protected void onstop () note that your activity is still in memory release as many resources as necessary save data to persistent storage protected void onstart() or protected void onrestart() verify that the right resources are available for your application e.g., GPS, network connections, WiFi 23

24 Intents Think of Intents as a verb and object; a description of what you want done examples: VIEW, CALL, PLAY, etc. System matches Intent with Activity that can best provide that service Activities and BroadcastReceivers describe what Intents they can service in their IntentFilters (via AndroidManifest.xml) 24

25 Broadcast receivers Components designed to respond to broadcast Intents think of them as a way to respond to external notifications or alarms Applications can invent and broadcast their own Intents as well 25

26 Services Faceless components that run in the background example: music player, network download, etc. Bind your code to a running service via a remote-able interface defined in an IDL Can run in your own process or separate process 26

27 Content Providers Enables sharing of data across applications examples: address book, photo gallery, etc. Provides uniform APIs for: querying (returns a Cursor) delete, update, and insert rows Content is represented by URI and MIME type 27

28 Android Debug Bridge Provides command line access to Android devicds adb shell -- starts the shell adb pull/push -- copy data from/to device adb uninstall - deletes an application 28