Lesson-6-Activity-lifecycle-and-state.pdf

Android Developer Fundamentals V2 Activities and Intents Lesson 6 This work is licensed under a Creative...

Android Developer Fundamentals V2 Activities and Intents Lesson 6 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android AndroidDeveloper DeveloperFundamentals FundamentalsV2 V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 1 License. Creative Commons Attribution 4.0 International License 2.2 Activity lifecycle and state This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 2 License. Creative Commons Attribution 4.0 International License Contents Activity lifecycle Activity lifecycle callbacks Activity instance state Saving and restoring Activity state This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity Lifecycle & Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License Android Developer Fundamentals V2 Managing State 3 License. Creative Commons Attribution 4.0 International License  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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 5 License. Creative Commons Attribution 4.0 International License What is the Activity Lifecycle? This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 6 License. Creative Commons Attribution 4.0 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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 7 License. Creative Commons Attribution 4.0 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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 9 License. Creative Commons Attribution 4.0 International License Activity states and callbacks graph This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 10 License. Creative Commons Attribution 4.0 International License Implementing and overriding callbacks Only onCreate() is required Override the other callbacks to change default behavior This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 11 License. Creative Commons Attribution 4.0 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 by onStart() This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 12 License. Creative Commons Attribution 4.0 International License onCreate(Bundle savedInstanceState) @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // The activity is being created. } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 13 License. Creative Commons Attribution 4.0 International License onStart() –> Started Called when the Activity is becoming visible to user Can be called more than once during lifecycle Followed by onResume() if the activity comes to the foreground, or onStop() if it becomes hidden This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 14 License. Creative Commons Attribution 4.0 International License onStart() @Override protected void onStart() { super.onStart(); // The activity is about to become visible. } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 15 License. Creative Commons Attribution 4.0 International License onRestart() –> Started Called after Activity has been stopped, immediately before it is started again Transient state Always followed by onStart() This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 16 License. Creative Commons Attribution 4.0 International License onRestart() @Override protected void onRestart() { super.onRestart(); // The activity is between stopped and started. } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 17 License. Creative Commons Attribution 4.0 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() This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 18 License. Creative Commons Attribution 4.0 International License onResume() @Override protected void onResume() { super.onResume(); // The activity has become visible // it is now "resumed" } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 19 License. Creative Commons Attribution 4.0 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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 20 License. Creative Commons Attribution 4.0 International License onPause() @Override protected void onPause() { super.onPause(); // Another activity is taking focus // this activity is about to be "paused" } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 21 License. Creative Commons Attribution 4.0 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 by either onRestart() if Activity is coming back to interact with user, or onDestroy() if Activity is going away This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 22 License. Creative Commons Attribution 4.0 International License onStop() @Override protected void onStop() { super.onStop(); // The activity is no longer visible // it is now "stopped" } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 23 License. Creative Commons Attribution 4.0 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 System may destroy Activity without calling this, so use onPause() or onStop() to save data or state This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 24 License. Creative Commons Attribution 4.0 International License onDestroy() @Override protected void onDestroy() { super.onDestroy(); // The activity is about to be destroyed. } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 25 License. Creative Commons Attribution 4.0 International License  Activity instance state Android Developer Fundamentals V2 26 When does config change? Configuration changes invalidate the current layout or other resources in your activity when the user: Rotates the device Chooses different system language, so locale changes Enters multi-window mode (from Android 7) This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 27 License. Creative Commons Attribution 4.0 International License What happens on config change? On configuration change, Android: 1. Shuts down Activity 2. Starts Activity over again by calling: by calling: onPause() onCreate() onStop() onStart() onDestroy() onResume() This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 28 License. Creative Commons Attribution 4.0 International License Activity instance state State information is created while the Activity is running, such as a counter, user text, animation progression State is lost when device is rotated, language changes, back-button is pressed, or the system clears memory This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 29 License. Creative Commons Attribution 4.0 International License  Saving and restoring Activity state Android Developer Fundamentals V2 30 What the system saves System saves only: ○ 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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 31 License. Creative Commons Attribution 4.0 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 This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 32 License. Creative Commons Attribution 4.0 International License onSaveInstanceState(Bundle outState) @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); // Add information for saving HelloToast counter // to the to the outState bundle outState.putString("count", String.valueOf(mShowCount.getText())); } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 33 License. Creative Commons Attribution 4.0 International License 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) This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 34 License. Creative Commons Attribution 4.0 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); } } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 35 License. Creative Commons Attribution 4.0 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); } } This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 36 License. Creative Commons Attribution 4.0 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. This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity lifecycle Android Developer Fundamentals V2 Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License and state 37 License. Creative Commons Attribution 4.0 International License Learn more Activities (API Guide) Activity (API Reference) Managing the Activity Lifecycle Pausing and Resuming an Activity Stopping and Restarting an Activity Recreating an Activity Handling Runtime Changes Bundle This work is licensed under a Creative Creative Commons Attribution 4.0 International License Activity Lifecycle Commons Attribution 4.0 International Creative Commons Attribution 4.0 International License Android Developer Fundamentals V2 and State 38 License. Creative Commons Attribution 4.0 International License END Android Developer Fundamentals V2 40