Lecture 6: Android XML, Inversion of Control, Timers (Handlers), Activity

Transcription

1 1 / 31 Lecture 6: Android XML, Inversion of Control, Timers (Handlers), Activity Engineering Design with Embedded Systems Patrick Lam University of Waterloo January 18, 2013

2 2 / 31 Housekeeping: Tutorials We ll make them more interactive. Goal: Have 2 TAs per tutorial to help with programming problems.

3 3 / 31 Assignment 2 I forgot to talk about Runnable last time. Sorry! If you use sleep(), you ll freeze the UI. I think we ll dock points for that. Please use the material I ll show you today.

4 4 / 31 XML is a structured document format. Has no intrinsic meaning.

5 5 / 31 Tree view of XML manifest uses-sdk application activity intent-filter <?xml version="1.0" encoding="utf-8"?> <manifest package="ca.patricklam.foo" android:versioncode="1"> <uses-sdk android:minsdkversion="10" android:targetsdkversion="16" /> <application <activity> <intent-filter> </intent-filter> </activity> </application> </manifest> Tags must be well-nested.

6 6 / 31 XML example <?xml version="1.0" encoding="utf-8"?> <manifest package="ca.patricklam.foo" android:versioncode="1"> <uses-sdk android:minsdkversion="10" android:targetsdkversion="16" /> root node attribute, name package, value ca.patricklam.foo. must quote all values, e.g. 1 self-closing tag <application application tag is nested within manifest tag <activity> more nesting <intent-filter> </intent-filter> </activity> </application> </manifest>

7 7 / 31 Inversion of Control: Without It Old ECE150 paradigm: 1. program start Operating System Your Program

8 8 / 31 Inversion of Control: Without It Old ECE150 paradigm: 1. program start Operating System Your Program 2. calls Library

9 9 / 31 Inversion of Control: Without It Old ECE150 paradigm: 1. program start Operating System Your Program 2. calls 3. returns Library

10 10 / 31 Inversion of Control: Without It Old ECE150 paradigm: 1. program start Operating System Your Program 4. program exit 2. calls 3. returns Library

11 11 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: Android 1. call create oncreate()

12 12 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: 1. call create oncreate() Android 2. register click listener

13 13 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: 1. call create oncreate() Android 3. return 2. register click listener

14 14 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: Android 1. call create oncreate() 4. return create 3. return 2. register click listener

15 15 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: Android 1. call create oncreate() 4. return create 3. return 2. register 5. click! click listener

16 16 / 31 Inversion of Control: With It New event-driven ECE155 paradigm: Android 1. call create oncreate() 4. return create 3. return 2. register 6. click return 5. click! click listener

17 17 / 31 Behind the Scenes for Inversion of Control Android is running an event loop for each thread: while (!done) { r <- fetch Runnable from Queue dispatch r } This is a polling loop: in particular, a tight polling loop, but which goes to sleep waiting for the next event (in fetch).

18 18 / 31 Timers in Android Goal: Make Android send you an event later. How? 1 Create a Handler object, say h. 2 Set up a Runnable object using an inner class. 3 Call h.postdelayed().

19 19 / 31 Timers in Android Goal: Make Android send you an event later. How? 1 Create a Handler object, say h. 2 Set up a Runnable object using an inner class. 3 Call h.postdelayed().

20 20 / 31 Handler objects Allow you to enqueue events on a message queue. These events will be executed later. Example: Handler h = new Handler();

21 21 / 31 Runnable objects A Runnable object encapsulates a task. Use inner class to specify a Runnable. You can put this code in oncreate() or initializealarm(): Runnable r = new Runnable() { public void run() { // execute the task } }

22 22 / 31 Enqueuing the Runnable object Finally, you need to make sure that the Runnable actually runs. This is easy: h.postdelayed(r, delayinms); (with the h and r objects from before).

23 23 / 31 About Android s Activity class An activity is a single, focused thing that the user can do. Usually a full-screen window. Examples: set up a timer; read off sensor values; make a phone call.

24 24 / 31 Broader Context: Tasks Applications may contain multiple activities. Android organizes activities into tasks. A task consists of a last-in, first-out stack of activities, possibly from different applications.

25 25 / 31 Task Navigation: Back button The Back button zaps the topmost activity on the stack. (from retrieved January 18, 2013)

26 Task Navigation: Switching Tasks Changing between tasks puts a different activity and its stack in the foreground, and puts the old activity in the background. (from http: //developer.android.com/images/fundamentals/diagram_multitasking.png, retrieved January 18, 2013) 26 / 31

27 27 / 31 Most Useful Activity Method: oncreate() Executed when the activity starts. Typical actions: set up the user interface, e.g.: create widgets; set up event listeners; PS. You must call super.oncreate().

28 28 / 31 Setting up the User Interface: Retrieving Widgets You ll use the findviewbyid() method. Need to cast the return value, e.g. tv = (TextView) findviewbyid(r.id.t); Must save the XML file to get the right ids.

29 Setting up the User Interface: Adding New Widgets Two steps. 1 Create the widget: tv = new TextView(getApplicationContext()); 2 Add it to the Activity: addview(tv); 29 / 31

30 30 / 31 Activity Lifecycle (from retrieved January 18, 2013)

31 Eclipse demo Plan: 1 Create a new Android project. 2 Add an EditText to the main Activity. 3 Use addtextchangedlistener to watch for changes in the text. 4 Use Quick Fix to get method stubs in the TextWatcher inner class. 5 Add code to the aftertextchanged method. 31 / 31