This is the presentation I gave in Google TLV office on Nov 2011. It talks about how Android manages tasks and the tools we have to manipulate and control the default behavior

1. Mastering Android Tasks

2. Why I am on stage?
Ran is Android GDE.
Ran knows how to use Impress
Ran spent lot of time on Android tasks.
Ran can break-dance.

4. Activities
Single UI screen.
Stacked like a deck of cards.
Only one is visible.
Only one is active.
New Activities are places on
top.

5. Activities
Application may have more than one Activity

6. Task
Collection of activities.
Organized in stack (i.e. “back stack”)
Task have at least one activity.
New activities placed on top
LIFO Queue
Each task has a “name” called Affinity.
Activity C
Activity B
Activity A

7. Tasks
Each app has at least one task
May have more
Tasks can be moved to “background”
Keeping their back stack.
User navigate between tasks
Easy switching between apps.
Multitasking experience.

8. User's Action
Home
(Foreground Task)
(Backgorund Tasks)

9. User's Action
Home
Ingress
(Foreground Task)
(Backgorund Tasks)

10. User's Action
Home
Ingress
Home
(Foreground Task)
(Backgorund Tasks)

11. User's Action
Home
Ingress
Home
G+
(Foreground Task)
(Backgorund Tasks)

12. User's Action
Home
Ingress
Home
G+
Enters Post
(Foreground Task)
(Backgorund Tasks)

13. User's Action
Home
Ingress
Home
G+
Enters Post
Home
(Foreground Task)
(Backgorund Tasks)

14. User's Action
Home
Ingress
Home
G+
Enters Post
Home
Flipboard
(Foreground Task)
(Backgorund Tasks)

15. User's Action
Home
Ingress
Home
G+
Enters Post
Home
Flipboard
Home
(Foreground Task)
(Backgorund Tasks)

16. User's Action
Home
Ingress
Home
G+
Enters Post
Home
Flipboard
Home
Recent Apps
(Foreground Task)
(Backgorund Tasks)

17. User's Action
Home
Ingress
Home
G+
Enters Post
Home
Flipboard
Home
Recent Apps
G+
(Foreground Task)
(Backgorund Tasks)

18. Why Manipulate?

19. Why Manipulate default behavior?
Multiple entry points to the app
Launcher
Notification
Share Intent
“Singleton” Activity
Activity that wants to share data between instances.
(example: browser)

20. Changing default behavior
<activity> tag attributes in AndroidManifest.xml
Launchmode
TaskAffinity
...
Adding flags to Intent used to launch the activity
FLAG_ACTIVITY_NEW_TASK
FLAG_ACTIVITY_CLEAR_TOP
FLAG_ACTIVITY_SINGLE_TOP
Warning – only sounds easy.

21. Android:taskAffinity
Used to determine the task that should hold the
activity
Task that has the same affinity value
By Default: all activities share the same affinity
(package name)
Task's affinity is the affinity of the activity that created
it (also called root activity)

22. Example
Manifest:
Activity A is launched

23. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

24. Example
Manifest:
Activity A is launched
Activity A's code:
Intent I = new Intent (this,ActvitiyB.class)
startActvitiy(i)
Activity A
Com.myApp

25. Example
Manifest:
Activity A is launched
Activity A's code:
Intent I = new Intent (this,ActvitiyB.class)
startActvitiy(i)
Activity B
Activity A
Com.myApp

26. What?

27. Why like this?
Activity B added to the same task although it had
different affinity
In order to create a new task – you need to add
FLAG_ACTIVITY_NEW_TASK to the launching
intent

28. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

29. Example
Manifest:
Activity A is launched
Activity A's code:
Intent I = new Intent (this,ActvitiyB.class)
I.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
startActvitiy(i)
Activity A
Com.myApp

30. Example
Manifest:
Activity A is launched
Activity A's code:
Intent I = new Intent (this,ActvitiyB.class)
I.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
startActvitiy(i)
Activity A
Com.myApp
Activity B
Com.something

31. Android:launchMode
Specifies how the Activity should be launched
Four different modes:
Standard (default)
Single Top
Single Task
Single Instance

32. Launch Mode: Standard
New instance is created in the calling activity's task
Activity can have multiple instances
Instances can reside in different tasks
One task can have multiple instances

33. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

34. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity A
Com.myApp

35. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B
Activity A
Com.myApp

36. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity B
Activity A
Com.myApp

37. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A
Activity B
Activity A
Com.myApp

38. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A launches Activity B (with flag NEW_TASK)
Activity A
Activity B
Activity A
Com.myApp

39. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A launches Activity B (with flag NEW_TASK)
Activity A
Activity B
Activity A
Com.myApp
Activity B
Com.something

40. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A launches Activity B (with flag NEW_TASK)
Activity B launches Activity A
Activity A
Activity B
Activity A
Com.myApp
Activity B
Com.something

41. Example
Manifest:
Activity A is launched
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A launches Activity B (with flag NEW_TASK)
Activity B launches Activity A
Activity A
Activity B
Activity A
Activity A
Activity B
Com.myApp
Com.something

42. Launch Mode: Single Top
If an instance of the activity is at the top of the stack –
new activity will not be create, instead –
onNewIntent() will be called.
Activity can have multiple instances
Instances can reside in different tasks
One task can have multiple instances

43. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

44. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
Activity A
Com.myApp

45. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
OnNewIntent(..)
Activity A
Com.myApp

46. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
Activity A launches Activity B (no flags)
OnNewIntent(..)
Activity A
Com.myApp

47. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
Activity A launches Activity B (no flags)
Activity B
Activity A
Com.myApp

48. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity B
Activity A
Com.myApp

49. Example
Manifest:
Activity A is launched
User pulls the notification bar and clicks on notification
that fires Activity intent to Activity A
Activity A launches Activity B (no flags)
Activity B launches Activity A
Activity A
Activity B
Activity A
Com.myApp

50. Launch Mode: Single Task
New task is created for the Activity and the Activity is
its root Activity
If an instance of the Activity already exists – system
will reroute the intent to onNewIntent() callback and
won't create new instance.
Activity can have only one instance
Activity is always the root of the task

51. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

52. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity A
Com.myApp

53. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity B
Activity A
Com.myApp

54. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity B launches Activity C with FLAG_NEW_TASK
Activity B
Activity A
Com.myApp

55. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity B launches Activity C with FLAG_NEW_TASK
Activity B
Activity A
Com.myApp
Activity C
Com.something

56. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity B launches Activity C with FLAG_NEW_TASK
Activity C launches Activity A
Activity B
Activity A
Com.myApp
Activity C
Com.something

57. Example
Manifest:
Activity A is launched
Acitivity A launches Activity B
Activity B launches Activity C with FLAG_NEW_TASK
Activity C launches Activity A
OnNewIntent(..)
Activity A
Com.myApp
Activity C
Com.something

58. Launch Mode: Single Instance
Same as Single Task except that it is the only activity
in its task
New activities will be launched in different tasks.
Activity can have only one instance
Activity is always the root of the task
Activity is the only member of its task

59. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

60. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity A
Com.myApp

61. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity A
Com.myApp
Activity B
Com.myApp

62. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C
Activity A
Com.myApp
Activity B
Com.myApp

63. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C
Activity C
Activity A
Com.myApp
Activity B
Com.myApp

64. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C
Activity C launches Activity A
Activity C
Activity A
Com.myApp
Activity B
Com.myApp

65. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C
Activity C launches Activity A
Activity C
OnNewIntent(..)
Activity A
Com.myApp
Activity B
Com.myApp

66. FLAG_ACTIVITY_NEW_TASK
Start the activity in a new task. If a task is already
running for the activity you are now starting, that task
is brought to the foreground with its last state restored
and the activity receives the new intent in
onNewIntent().

67. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

68. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity A
Com.myApp

69. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B
Activity A
Com.myApp

70. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp

71. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp
Activity C
Com.something

72. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
Activity B
Activity A
Com.myApp
Activity C
Com.something

73. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

74. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

75. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

76. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
onResume()
User switches to com.myApp
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

77. Easy – but may be tricky

78. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

79. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity A
Com.myApp

80. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B
Activity A
Com.myApp

81. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp

82. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp
Activity C
Com.something

83. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
Activity B
Activity A
Com.myApp
Activity C
Com.something

84. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

85. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

86. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B launches Activity D with
FLAG_NEW_TASK
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

87. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B launches Activity D with
FLAG_NEW_TASK
Activity D
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

88. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D
User switches to com.myApp
Activity B launches Activity D with
FLAG_NEW_TASK
Activity D
Activity B
Activity D
Activity A
Activity C
Com.myApp
Com.something

89. New instance of D created!

90. Why another Instance was created?
A matching task is a task that has the same launching
intent as the intent used to launch the activity.
Although Activity D has the same affinity as the task
that was created by Activity C, the launching intent is
different.
The result: instead of onResume() - > new Instance.

91. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

92. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity A
Com.myApp

93. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B
Activity A
Com.myApp

94. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp

95. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp
Activity C
Com.something

96. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D and calls finish()
Activity B
Activity A
Com.myApp
Activity C
Com.something

97. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D and calls finish()
Activity B
Activity A
Com.myApp
Activity C
D
Com.something

98. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D and calls finish()
User switches to com.myApp
Activity B
Activity A
Com.myApp
Activity C
D
Com.something

99. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D and calls finish()
User switches to com.myApp
Activity B launches Activity C with
FLAG_NEW_TASK
Activity B
Activity A
Com.myApp
Activity C
D
Com.something

100. Example
Manifest:
Activity A is launched
Activity A launches Activity B
Activity B launches Activity C with
FLAG_NEW_TASK
Activity C launches Activity D and calls finish()
User switches to com.myApp
Activity B launches Activity C with
FLAG_NEW_TASK
onResume()
Activity B
Activity A
Com.myApp
Activity C
D
Com.something

101. Asked for Activity C - > Got activiy D.

102. It is not over yet...

103. Example
Manifest:
Activity A is launched
Activity A
Com.myApp

104. Example
Manifest:
Activity A is launched
Activity A launches Activity B with
startActivityForResult()
Activity A
Com.myApp

105. Example
Manifest:
Activity A is launched
Activity A launches Activity B with
startActivityForResult()
OnActivityResult(...)
Activity A
Com.myApp

106. Example
Manifest:
Activity A is launched
Activity A launches Activity B with
startActivityForResult()
Activity A
Com.myApp
Activity B
Com.myApp

107. StartActivityForResult
If an activity calls startActivityForResult and new task
is created – onActivityResult is called immediately.
“its not bug – its a feature” approach.

108. Tips
Abd shell dumpsys activity
Don't wait for the end of the development to apply
flags, affinities and launch modes.
It is iterative on-going process.

109. Questions?
ran@mobiliup.com
+Ran Nachmany