Activities in the Wild: Exploring the Activity Lifecycle (Connect.Tech, October 2016)

[This version of the talk includes more details about handling multi-window scenarios. You can view a video of the presentation here: https://www.youtube.com/watch?v=Q5FWJGHuDwA]

To Android users, your Activity object is your app. Take a journey with me to experience what happens to your Activity’s state and view at runtime in relation to what the user (and the operating system itself) is doing. We will discuss considerations you should make based on this knowledge when designing and building your app. You will walk away from this talk with a strong understanding of the most fundamental piece of Android applications.

Transcript

1. Activities in the Wild Exploring the Activity Lifecycle Kristin Marsicano @kristinmars Big Nerd Ranch
2. Demo: Multi-Tasking
3. Goal for Today Empower you to reason about the Activity lifecycle so you can provide a smooth user experience
6. What is the Activity Lifecycle? Why
7. Activity public class TickerActivity extends AppCompatActivity { private int mCount = 0;
 ...
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_ticker);
 setupUI();
 updateUI();
 }
 
 ... }
 TickerActivity.java: <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout ...>
 
 <TextView ... />
 
 <TextView ... />
 
 <Button … />
 
 </LinearLayout>
 activity_ticker.xml:
8. Activity Manager
9. Activity Manager User clicks Ticker icon on Launch Screen
10. Activity Manager User clicks Ticker icon on Launch Screen
11. Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity
12. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity
13. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity
14. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity Spin up app process
15. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity Spin up app process Create TickerActivity instance
16. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity Spin up app process Create TickerActivity instance Move TickerActivity to Foreground
17. Activity Manager Activity Manager User clicks Ticker icon on Launch Screen Intent: TickerActivity Spin up app process Create TickerActivity instance Move TickerActivity to Foreground
18. Android OS App Processes Launcher Contacts
19. Android OS TerrificTicker App Processes Launcher Contacts
20. Android OS TerrificTicker App Processes Launcher Contacts
21. Android OS TerrificTicker One Foreground Activity Launcher Contacts Foreground Activity: What user sees
22. Activity Lifecycle
23. Activity Lifecycle Non- existent Stopped Paused Resumed Set of states Activity can be in
24. Activity States
25. Activity States State
26. Activity States State In memory?
27. Activity States State In memory? Visible to user?
28. Activity States State In memory? Visible to user? In foreground?
29. Activity States State In memory? Visible to user? In foreground?
30. Activity States State In memory? Visible to user? In foreground? Non-Existent No No No
31. Activity States State In memory? Visible to user? In foreground? Non-Existent No No No Stopped Yes No No
32. Activity States State In memory? Visible to user? In foreground? Non-Existent No No No Stopped Yes No No Paused Yes Yes/Partially No
33. Activity States State In memory? Visible to user? In foreground? Non-Existent No No No Stopped Yes No No Paused Yes Yes/Partially No Resumed (aka Active, Running) Yes Yes Yes
34. Activity in the Wild
35. Activity in the Wild
36. Activity Lifecycle
37. Activity Lifecycle Non- existent Stopped Paused Resumed Set of states Activity can be in
38. Activity Lifecycle Non- existent Stopped Paused Resumed Set of states Activity can be in Rules about when/how state changes
39. Activity Lifecycle Non- existent Stopped Paused Resumed Set of states Activity can be in Rules about when/how state changes onDestroy() onCreate() onPause() onResume() onStart() onStop() Set of callback methods
40. User Launches Activity Lifecycle by Example 1 of 5: “Build-up”
41. Example: Launch TickerActivity
42. Example: Launch TickerActivity Press Icon
43. Example: Launch TickerActivity
44. Laser Focus: Ticker Activity Android OS
45. Start in Non-Existent State Non- existent Android OS
46. User Launches App Non- existent Android OS User presses icon
47. onCreate() Non- existent Android OS TerrificTicker Process Instance Created Ticker Activity mCount = 0 Stopped Instance Created onCreate()
48. Android OS onStart() Paused onStart() Non- existent Stopped Instance Created onCreate() TerrificTicker Process Ticker Activity mCount = 0
49. onResume() Resumed onResume() Paused onStart() Non- existent Stopped Instance Created onCreate() Android OS TerrificTicker Process Ticker Activity mCount = 0
50. Pressing Back Lifecycle by Example 2 of 5: “Tear down”
51. User Increments Count Resumed onResume() Paused onStart() Non- existent Stopped Instance Created onCreate() Android OS TerrificTicker Process Ticker Activity mCount = 0 Press button
52. User Increments Count Resumed onResume() Paused onStart() Non- existent Stopped Instance Created onCreate() Android OS TerrificTicker Process Ticker Activity mCount = 0 Press button Ticker Activity mCount = 1
53. User Increments Count Resumed onResume() Paused onStart() Non- existent Stopped Instance Created onCreate() Android OS TerrificTicker Process Ticker Activity mCount = 0 Press button 1 Ticker Activity mCount = 1
54. User Presses Back Non- existent Stopped Instance Created onCreate() Paused Resumed onResume() onStart() Press Back Android OS TerrificTicker Process Ticker Activity mCount = 1 1
55. onPause() Non- existent Stopped Instance Created onCreate() Paused Resumed User presses back onPause() onResume() onStart() Android OS TerrificTicker Process Ticker Activity mCount = 1 1
56. onStop() onStop() Non- existent Stopped Instance Created onCreate() Paused Resumed User presses back onPause() onResume() onStart() Android OS TerrificTicker Process Ticker Activity mCount = 1
57. onDestroy() onDestroy() Instance Destroyed Non- existent Stopped Instance Created onCreate() Paused Resumed User presses back onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 1
58. onDestroy() onDestroy() Instance Destroyed Non- existent Stopped Instance Created onCreate() Paused Resumed User presses back onPause() onResume() onStart() onStop() Android OS TerrificTicker Process
59. User Launches App Again Android OS User presses icon TerrificTicker Process Non- existent
60. User Launches App Again Android OS User presses icon TerrificTicker Process Non- existent What will the user see? 0 (0) 1 (1)
61. Answer: (0) Android OS TerrificTicker Process Ticker Activity mCount = 0 0 Non- existent Stopped onCreate() Paused Resumed onResume() onStart()
62. Pressing Home Lifecycle Example 3 of 5: “Switching Tasks”
63. Increment Count Twice
64. 1 Increment Count Twice
65. 1 Increment Count Twice 2
66. 1 Increment Count Twice 2 Press home
67. Home Screen
68. TickActivity is Running onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 2 0 2
69. User Presses Home onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 2 0 2 User presses Home
70. onPause() onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() 2 Android OS TerrificTicker Process Ticker Activity mCount = 2
71. onStop() onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 2
72. User Launches App Again Android OS User presses icon TerrificTicker Process Ticker Activity mCount = 2 Stopped
73. User Launches App Again Android OS User presses icon TerrificTicker Process Ticker Activity mCount = 2 Stopped What will the user see? 0 (0) 2 (2)
74. Answer: (2) onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 2 2
75. Launching Another Activity Lifecycle Example 4 of 5: “Fully occlude TickerActivity”
76. Launch TickerActivity Press Icon
77. 0 Increment Count Press three times
78. 0 1 Increment Count Press three times
79. 0 1 Increment Count 2 Press three times
80. 0 1 Increment Count 2 Press three times 3
81. Launch SaveActivity Press Save Count
82. SaveActivity is Running
83. From the Start: TickerActivity is Running onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
84. Use Presses Save onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
85. SaveActivity Launches Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
86. TickerActivity: Stopped onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
87. User Presses Back onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
88. SaveActivity is Destroyed Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
89. SaveActivity is Destroyed Android OS TerrificTicker Process Ticker Activity mCount = 3
90. Ticker Activity Moves to Stopped from Running Android OS TerrificTicker Process Ticker Activity mCount = 3 onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop()
91. onStart() onStart() Android OS TerrificTicker Process Ticker Activity mCount = 3 onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStop()
92. onStart() onStart() Android OS TerrificTicker Process Ticker Activity mCount = 3 onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStop()
93. onStart() onResume() Android OS TerrificTicker Process Ticker Activity mCount = 3 onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStop()
94. Launching a Transparent Activity Lifecycle Example 5 of 5: “Partially occlude TickerActivity”
95. Launch SaveActivity Press Save Count
96. SaveActivity is Running
97. From the Start: TickerActivity is Running onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
98. Use Presses Save onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
99. SaveActivity Launches Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
100. TickerActivity: Paused onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity
101. User Presses Back Android OS TerrificTicker Process Ticker Activity mCount = 3 Save Activity onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop()
102. User Presses Back Android OS TerrificTicker Process Ticker Activity mCount = 3 onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop()
103. TickerActivity: Running onDestroy() Non- existent Stopped onCreate() Paused Resumed onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
104. Lifecycle Summary Exists? Visible? Foreground?
105. Activity Lifecycle onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
106. Entire Lifetime (Instance Lifetime) Instance Lifetime onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
107. Entire Lifetime Visible Lifetime Visible Lifetime onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
108. Entire Lifetime Foreground Lifetime Visible Lifetime onDestroy() Non- existent Stopped onCreate() Foreground Lifetime Paused Running onPause() onResume() onStart() onStop()
109. Going Home, Revisited A Cautionary Tale
110. Launch TickerActivity
111. Do Lots of Work 42
112. Press Home 42
113. Launch Pokemon Go
114. Play Pokemon GO
115. Press Home
116. Press Ticker Icon
117. Launch Ticker
118. Launch Ticker
119. User Presses Home onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() User presses home 3 Android OS TerrificTicker Process Ticker Activity mCount = 3
120. onPause() onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() 3 Android OS TerrificTicker Process Ticker Activity mCount = 3
121. onStop() onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3
122. User Plays Pokemon GO onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3 Pokemon GO Process VideoActivity
123. Uh oh… onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() Android OS TerrificTicker Process Ticker Activity mCount = 3 VideoPlayer Process VideoActivity
124. Ticker Process Gets Killed onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() X Android OS TerrificTicker Process Ticker Activity mCount = 3 VideoPlayer Process VideoActivity X
125. TickerActivity Jumps to Non- Existent onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() X Android OS VideoPlayer Process VideoActivity
126. Pre-Honeycomb onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop() X Android OS VideoPlayer Process VideoActivity X
127. Saving Transient State onSaveInstanceState to the rescue
128. onSaveInstanceState() public class TickerActivity extends AppCompatActivity {
 
 private static final String KEY_TICKER_COUNT = "ticker_count";
 ...
 
 @Override
 protected void onSaveInstanceState(Bundle outState) {
 super.onSaveInstanceState(outState);
 outState.putInt(KEY_TICKER_COUNT, mCount);
 } ...
 }

129. public class TickerActivity extends AppCompatActivity {
 
 ... 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_ticker);
 setupUI();
 
 if (savedInstanceState != null) {
 mCount = savedInstanceState.getInt(KEY_TICKER_COUNT, 0);
 }
 
 updateUI();
 } ...
 }
 Using State Bundle
130. Activity Record Stored 3 Activity Record Store Instance A
131. Activity Record Stored 3 Activity Record Store onSaveInstanceState ticker_count: 3 Instance A
132. Activity Record Stored 3 Activity Record Store onSaveInstanceState ticker_count: 3 TerrificTicker Instance A Record ticker_count: 3 Instance A
133. Process Gets Killed Activity Record Store TerrificTicker Instance A Record ticker_count: 3
134. User Launches App Activity Record Store TerrificTicker Instance A Record ticker_count: 3
135. User Launches App Activity Record Store TerrificTicker Instance A Record ticker_count: 3 onCreate ticker_count: 3
136. User Launches App Activity Record Store TerrificTicker Instance A Record ticker_count: 3 3 Recreated Instance A onCreate ticker_count: 3
137. User Launches App Activity Record Store 3 Recreated Instance A onCreate ticker_count: 3
138. User Launches App Activity Record Store 3 Recreated Instance A
139. Full Circle
140. Full Circle
141. Structuring your Activity What to put in each callback?
142. Lifecycle Pairs • onCreate / onDestroy • onStart / onStop • onResume / onPause
143. onCreate • call setContentView() • “hook up” UI widgets • check for saved state bundle
144. onPause • save vital data (pre-Honeycomb) • typically stop animations or other things consuming CPU (pre-Nougat) • should be quick
145. onStop • save vital data (Honeycomb and beyond) • typically stop animations or other things consuming CPU (in a multi-window world) • should be quick
146. onDestroy • last place to free resources
147. But Also… • It depends!
148. Reasoning About the Lifecycle What to put in each callback?
149. Challenge: Multi-Window What state is each in?
150. Entire Lifetime Foreground Lifetime Visible Lifetime onDestroy() Non- existent Stopped onCreate() Foreground Lifetime Paused Running onPause() onResume() onStart() onStop()
151. Example: Displaying Location • Show user their location • Minimize battery usage • Maximize precision when user is actively looking at my map
152. Displaying Location: Which Callbacks? • Start sampling when visible • Increase accuracy when in foreground • Set lower sampling rate/accuracy • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
153. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground • Set lower sampling rate/accuracy • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
154. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground • Set lower sampling rate/accuracy • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
155. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground onResume • Set lower sampling rate/accuracy • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
156. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground onResume • Decrease accuracy when in background • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
157. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground onResume • Decrease accuracy when in background onPause • Stop sampling - onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
158. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground onResume • Decrease accuracy when in background onPause • Stop sampling onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
159. Displaying Location: Which Callbacks? • Start sampling when visible onStart • Increase accuracy when in foreground onResume • Decrease accuracy when in background onPause • Stop sampling onStop onDestroy() Non- existent Stopped onCreate() Paused Running onPause() onResume() onStart() onStop()
160. Video Playback • Play video whenever player is visible • Stop playing video when player is not visible
161. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible - onStart • Pause playback not visible - onStop • Release player when user dismisses player - onDestroy
162. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible • Pause playback not visible - onStop • Release player when user dismisses player - onDestroy
163. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible onStart • Pause playback not visible - onStop • Release player when user dismisses player - onDestroy
164. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible onStart • Pause playback not visible • Release player when user dismisses player - onDestroy
165. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible onStart • Pause playback not visible onStop • Release player when user dismisses player - onDestroy
166. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible onStart • Pause playback not visible onStop • Release resources when user dismisses player onDestroy
167. Video Playback: Which Callbacks? • Initialize player onCreate • Start playback when visible onStart • Pause playback not visible onStop • Release resources when user dismisses player onDestroy
168. Stop used to be lazy! Pre-Nougat: onStop() can occur a short time after activity disappears from view
169. Video Playback: Which Callbacks? • Start playback when visible • > 23: onStart • <= 23: onResume • Pause playback not visible • > 23: onStop • <= 23: onPause
170. @Override
 public void onStart() {
 super.onStart();
 if (Util.SDK_INT > 23) {
 // play
 }
 }
 
 @Override
 public void onResume() {
 super.onResume();
 if ((Util.SDK_INT <= 23 || player == null)) {
 // play
 }
 }
 
 @Override
 public void onPause() {
 super.onPause();
 if (Util.SDK_INT <= 23) {
 // pause
 }
 }
 
 @Override
 public void onStop() {
 super.onStop();
 if (Util.SDK_INT > 23) {
 // pause
 }
 }
171. Next Steps
172. @kristinmars github.com/kristinmars bignerdranch.com