Objects First with Java Class Business © David J. Barnes and Michael Kölling

Activity An Activity is the main object in an Android app. Lifecycle:

Better Ways to Organize the Code There are several times when the code is organized around an integer return value. onCreateDialog() onOptionsItemSelected() onActivityResult() This results in a string of “if…then…else” code that just stinks.

Better Ways to Organize the Code Use a table of classes. Do a table lookup of the code and Java reflection to call the right class.

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Starting New Activities A common action for an activity is to start another activity. When another activity is started, the current activity is stopped and the new activity is created/started/resumed.

Starting New Activities: Intents Intents are communications about classes or executables or data Example: communicate which activity to start by creating an intent that indicates the class to use

Starting New Activities Two ways to start an activity To start an independent activity that will run, use startActivity() To start an activity that will return information to the current activity, use startActivityForResult() Both calls use intents to indicate which activity should start up

startActivity() Uri smsUri = Uri.parse("tel:"+grades.getStudent(itemPosition). getMobilePhoneNumber()); Intent sendIntent = new Intent(Intent.ACTION_VIEW, smsUri); sendIntent.putExtra("address", grades.getStudent(itemPosition).getMobilePhoneNumber()); sendIntent.putExtra("sms_body", "type message here"); sendIntent.setType("vnd.android-dir/mms-sms"); startActivity(sendIntent);

startActivityForResult() Using this call, one gives the intent AND a returning value that identifies the activity. When the Activity is completed, the method onActivityResult() is called.

startActivityForResult() Intent gameIntent = new Intent(this, GameDisplay.class); startActivityForResult( gameIntent, R.id.class_display_games);

startActivityForResult() protected void onActivityResult( int requestCode, int resultCode, Intent intent) { super.onActivityResult( requestCode, resultCode, intent); if (resultCode != RESULT_OK) return; if (intent != null) { if (requestCode == R.id.class_display_games) { … }

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Returning From an Activity To halt an Activity, call finish() To return to the Activity that created the current Activity, call setResult(): setResult(RESULT_OK, result); This means automatic return with the ID that it was created with.

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Information in Intents You can insert information into an intent to communicate with the activity that is being started. The typical way is to Create a Bundle Put things into the Bundle Add the Bundle to the Intent through putExtras()

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Retrieving Information Use the getIntent() call to retrieve the Intent Use the get…() call to get the extra you are looking for

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Exercise: XML File

Interface Component Overview