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CMSC 628: Introduction to Mobile Computing

CMSC 628: Introduction to Mobile Computing. Nilanjan Banerjee. University of Maryland Baltimore County nilanb@umbc.edu http://csee.umbc.edu/~nilanb/teaching/628/. Introduction to Mobile Computing. Today’s lecture. Finish discussion on the app we were building

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CMSC 628: Introduction to Mobile Computing

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  1. CMSC 628: Introduction to Mobile Computing Nilanjan Banerjee University of Maryland Baltimore County nilanb@umbc.edu http://csee.umbc.edu/~nilanb/teaching/628/ Introduction to Mobile Computing

  2. Today’s lecture • Finish discussion on the app we were building • Ways to write OnClickListener() • How to interact with other activities • Use implicit and explicit Intents. • Android Lifecycle • Activity starts up • Activity suspends and resumes • Activity is stopped and restarted.

  3. Starting an activity • Activity starts • onCreate(), onStart(),onResume() are called in succession onStart() Activity is partially visible Ack: Android Development website

  4. Pausing and Resuming an Activity • How is pausing defined? • If an activity is partially visible in the background • Dialog boxes open up • Method called is onPause() What should you do before an activity pauses save state of the application? release resources

  5. Stopping and Starting an Activity • How is stopping an activity defined? • If the activity is not visible • Press back or home button • Start a new activity or receive a phone call What should you do before an activity stops save state of the application? release resources System destroys the activity

  6. Recreating an Activity • If the system destroys an activity due to system constraints • Saves certain state of your activity that is restored back the next time the activity starts • If you want to save your own state before the activity is destroyed: • Override the onSaveInstanceState(Bundle) • Access your state during onCreate() or onRestoreInstanceState()

  7. How is this implemented using Intents Specify an intent Action: broadly defined the Intent [SEND --- send something VIEW --- view something CALL --- call somebody] Data: e.g., URI, email [email message etc] Application Invokes an activity Table System [Activity, action]

  8. In some cases you also need results back from an activity subActivity Application Get result back Do stuff

  9. Small project for today. requestCode with startActivity Camera Application Application Callback [onActivityResult(int, int, Intent)] int ---- requestCode int --- result Intent --- Intent that stores any data Takes a picture

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