Chapter 6 - android activity.pptx

Android Developer Fundamentals V2 Activities Lesson 5 Activity This work is licensed under a Android AndroidDeveloper Developer lifecycle and...

Android Developer Fundamentals V2 Activities Lesson 5 Activity This work is licensed under a Android AndroidDeveloper Developer lifecycle and Creative Commons Attribution 4.0 1 Fundamentals FundamentalsV2 V2 International License Soft reminder: Assessment Assessment 1 (10%) : Quiz1 (Done) Assessment 2 (30%) : Lab Assignments (Done) Assessment 3 (30%) : Project (Project Application 20%, Report 10%) - 26/06/2024 (Week 13) Assessment 4 (30%) : Final Assessment (Theory + Programming) - 03/07/2024 (Week 14) Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 2 Fundamentals V2 International License Contents Activity lifecycle Activity lifecycle callbacks Activity instance state Saving and restoring Activity state This work is licensed under a Activity Android Developer Creative Commons Attribution 4.0 3 Lifecycle & International License Fundamentals V2  Activity lifecycle Android Developer Fundamentals V2 4 What is the Activity Lifecycle? The set of states an Activity can be in during its lifetime, from when it is created until it is destroyed More formally: A directed graph of all the states an Activity can be in, and the callbacks associated with transitioning from each state to the next one Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 5 Fundamentals V2 International License What is the Activity Lifecycle? Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 6 Fundamentals V2 International License Activity states and app visibility Created (not visible yet) Started (visible) Resume (visible) Paused(partially invisible) Stopped (hidden) Destroyed (gone from memory) State changes are triggered by user action, configuration changes such as device rotation, or system action Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 7 Fundamentals V2 International License  Activity lifecycle callbacks Android Developer Fundamentals V2 8  Callbacks and when they are called onCreate(Bundle savedInstanceState)—static initialization onStart()—when Activity (screen) is becoming visible onRestart()—called if Activity was stopped (calls onStart()) onResume()—start to interact with user onPause()—about to resume PREVIOUS Activity onStop()—no longer visible, but still exists and all state info preserved onDestroy()—final call before Android system destroys Activity Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 9 Fundamentals V2 International License Activity states and callbacks graph Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 10 Fundamentals V2 International License View more: https://www.youtube.com/watch?v=SJw3Nu_h8kk Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 11 Fundamentals V2 International License onCreate() –> Created Called when the Activity is first created, for example when user taps launcher icon Does all static setup: create views, bind data to lists,... Only called once during an activity's lifetime Takes a Bundle with Activity's previously frozen state, if there was one Created state is always followed Android Developer by onStart() This work is licensed under a Activity Creative Commons Attribution 4.0 lifecycle and International License 12 Fundamentals V2 onCreate(Bundle savedInstanceState) @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // The activity is being created. } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 13 Fundamentals V2 International License onStart() –> Started Called when the Activity is becoming visible to user Can be called more than once during lifecycle Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 14 Fundamentals V2 International License onStart() @Override protected void onStart() { super.onStart(); // The activity is about to become visible. } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 15 Fundamentals V2 International License onRestart() –> Started Called after Activity has been stopped, immediately before it is started again Transient state Always followed by onStart() Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 16 Fundamentals V2 International License onRestart() @Override protected void onRestart() { super.onRestart(); // The activity is between stopped and started. } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 17 Fundamentals V2 International License onResume() –> Resumed/Running Called when Activity will start interacting with user Activity has moved to top of the Activity stack Starts accepting user input Running state Always followed by onPause() Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 18 Fundamentals V2 International License onResume() @Override protected void onResume() { super.onResume(); // The activity has become visible // it is now "resumed" } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 19 Fundamentals V2 International License onPause() –> Paused Called when system is about to resume a previous Activity The Activity is partly visible but user is leaving the Activity Typically used to commit unsaved changes to persistent data, stop animations and anything that consumes resources Implementations must be fast because the next Activity is not resumed until this method returns Followed by either onResume() if the Activity returns back to the front, or onStop() if it becomes invisible to the user Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 20 Fundamentals V2 International License onPause() @Override protected void onPause() { super.onPause(); // Another activity is taking focus // this activity is about to be "paused" } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 21 Fundamentals V2 International License onStop() –> Stopped Called when the Activity is no longer visible to the user New Activity is being started, an existing one is brought in front of this one, or this one is being destroyed Operations that were too heavy-weight for onPause() Followed byAndroid either onRestart() Developer Activity if Activity is This work is licensed under a Creative Commons Attribution 4.0 lifecycle and 22 Fundamentals V2 International License onStop() @Override protected void onStop() { super.onStop(); // The activity is no longer visible // it is now "stopped" } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 23 Fundamentals V2 International License onDestroy() –> Destroyed Final call before Activity is destroyed User navigates back to previous Activity, or configuration changes Activity is finishing or system is destroying it to save space Call isFinishing() method to check Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 24 Fundamentals V2 International License onDestroy() @Override protected void onDestroy() { super.onDestroy(); // The activity is about to be destroyed. } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 25 Fundamentals V2 International License  Activity instance state Android Developer Fundamentals V2 26 Activity instance state State information is created while the Activity is running, such as a counter, user text, animation progression A user expects an activity's UI state to remain the same throughout a configuration change, such as rotation or switching into multi-window mode. However, by default the system destroys the activity when such a configuration change occurs, wiping away any UI state stored in the activity instance. Further reading: https://developer.android.com/topic/libraries/architecture/saving-states Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 29 Fundamentals V2 International License Saving and restoring Activity state Android Developer Fundamentals V2 30 What the system saves System only save: ○ State of views with unique ID (android:id) such as text entered into EditText ○ Intent that started activity and data in its extras You are responsible for saving other activity and user progress data Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 31 Fundamentals V2 International License Saving instance state Implement onSaveInstanceState() in your Activity Called by Android runtime when there is a possibility the Activity may be destroyed Saves data only for this instance of the Activity during current session Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 32 Fundamentals V2 International License onSaveInstanceState(Bundle outState) @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); // Add information for saving HelloToast counter // to the outState bundle outState.putString("count", Activity This work is licensed under a String.valueOf(mShowCount.getText())); Android Developer Fundamentals V2 lifecycle and Creative Commons Attribution 4.0 International License 33 Restoring instance state Two ways to retrieve the saved Bundle in onCreate(Bundle mySavedState) Preferred, to ensure that your user interface, including any saved state, is back up and running as quickly as possible Implement callback (called after onStart()) onRestoreInstanceState(Bundle mySavedState) Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 34 Fundamentals V2 International License  Restoring in onCreate() @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mShowCount = findViewById(R.id.show_count); if (savedInstanceState != null) { String count = savedInstanceState.getString("count"); if (mShowCount != null) mShowCount.setText(count); } } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 35 Fundamentals V2 International License  onRestoreInstanceState(Bundle state) @Override public void onRestoreInstanceState (Bundle mySavedState) { super.onRestoreInstanceState(mySavedState); if (mySavedState != null) { String count = mySavedState.getString("count"); if (count != null) mShowCount.setText(count); } } Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 36 Fundamentals V2 International License Instance state and app restart When you stop and restart a new app session, the Activity instance states are lost and your activities will revert to their default appearance If you need to save user data between app sessions, use shared preferences or a database. Activity This work is licensed under a Android Developer lifecycle and Creative Commons Attribution 4.0 37 Fundamentals V2 International License  Consider user END experience in mobile Thank you app development Android Developer Fundamentals V2 38