Android Services

In this talk we show the different types of Services that exist in Android and how we can use them in our applications to perform operations in the background. GDG DevFest Sur 2013. #DevFestSur

The sample codes used in this talk can be found at GitHub: https://github.com/josejuansanchez/GDG-DevFestSur-2013

Transcript

1. Android  Services  
   José  Juan  Sánchez  Hernández  
   @josejuansanchez  
   

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2. Ac7vi7es  
   Ac7vi7es  
   Ac7vi7es  
   Ac7vi7es  
   Ac7vi7es  
   Services  
   Ac7vi7es  
   Ac7vi7es  
   Receivers  
   Ac7vi7es  
   Ac7vi7es  
   Providers  
   Dalvik  VM  
   Libs  
   DB  
   Files  
   res  
   Android  Applica7on  Anatomy  
   Process  
   Applica7on  /  APK  Package  
   Applica7on  =  Set  of  Android  Components  
    
   •  It  contains  any  number  of  Ac#vi#es,  
   Services,  Receivers  and  Providers.  
    
   •  It  has  its  own  file  system,  database,  
   place  to  store  na7ve  libraries.  
    
   •  No  other  app  can  access  any  of  its  
   data  without  prior  permission.  
   2/36  
   

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3. Process  
   Applica7on  /  APK  Package  
   Run7me  Overview  
   Image:  Marko  Gargenta  
   Android  Internals  Overview  
   3/36  
   

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4. Process  
   Applica7on  /  APK  Package  
   Zygote  
   4/36  
   

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5. Process  
   Applica7on  /  APK  Package  
   Process  Basics  
   •  Android  Process  ==  Linux  Process.  
   •  By  default,  1  Process  per  APK.  
   •  By  default,  1  Thread  per  Process.  
    
   Threads  on  Android  
   •  By  default,  each  process  has  1  thread.  
   •  Mosts  components  share  the  single  thread.  
   Threads  and  Loopers  
   •  Each  thread  has  a  Looper  to  handle  a  message  queue.  
   •  Events  from  all  components  are  interleaved  into  Looper.    
              E.g.  View  UI  events,  IntentReceivers  firing,  etc.  
   •  Loopers  cannot  accommodate  mul7-­‐threaded  access.    
            They  are  designed  to  play  nicely  with  MessageHandlers.  
   Processes  and  Threads  
   5/36  
   

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6. Ac7vity  
   Service  
   Main  Thread  
    
    
    
    
    
    
    
   Looper  
   Message  
   Queue  
   System  
   Events  
   UI  
   Events  
   Process  
   Applica7on  /  APK  Package  
   Processes  and  Threads  
   6/36  
   

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7. Services  
   7/36  
   What  is  a  Service?  
   •  Is  a  component  that  can  perform  long-­‐running  opera7ons  in  the  background.  
   •  They  can  be  started  and  stopped.  
   •  Services  doesn't  have  UI  and  does  not  provide  direct  access  to  the  UI.  
    
   What  a  Service  is  NOT?  
   •  A  Service  is  not  a  separate  process.  
   •  A  Service  is  not  a  thread.  
   Examples  
   •  Playing  music  even  if  the  player  ac7vity  gets  garbage-­‐collected.  
   •  Polling  the  Internet  for  RSS/Atom  feed  updates.  
   •  Performing  periodic  work  without  user  interven7on  (scheduled  tasks).  
   •  An  applica7on  that  con7nually  logs  the  geographical  coordinates  of  the  device.  
    
   

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8. Process  
   Applica7on  /  APK  Package  
   Started  
   A  service  is  “started”  when  an  
   applica7on  component  starts  it  by  
   calling  startService().  Oien  
   performs  a  single  opera7on  &  might  
   not  return  a  result  to  the  caller  
   directly.  
    
   Bound  
   A  service  is  “bound”  when  an  
   applica7on  component  binds  to  it  by  
   calling  bindService().  Provides  a  
   client-­‐  server  interface  that  allows  for  
   a  conversa7on  with  the  Service.  
   Types  of  Services  
   Android  Developers.  API  Guides  
   hkps://developer.android.com/guide/components/services.html  
   8/36  
   

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9. Applica7on  /  APK  Package  
   Started  Services  
   There  are  two  classes  you  can  extend  to  create  a  started  service:  
   Service  and  IntentService  
    
   9/36  
   

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10. Ac7vity  
    Service  
    Main  Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    System  
    Events  
    UI  
    Events  
    Process  
    Applica7on  /  APK  Package  
    Example:  LocalService  /  1  Process  
    10/36  
    Bad  Prac7ce!  May  block  the  Main  Thread  L  
    

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11. Example:  LocalService  /  1  Process  
    11/36  
    

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12. Example:  LocalService  /  1  Process  
    12/36  
    

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13. The  service  should  remain  stopped  un7l    
    explicitly  started  by  applica7on  code  
    13/36  
    

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14. Example:  LocalService  /  1  Process  
    14/36  
    START_NOT_STICKY
    If  the  system  kills  the  service,  do  not  recreate  the  service,  unless  there  are  pending  intents  
    to  deliver.  This  is  the  safest  op7on  to  avoid  running  your  service  when  not  necessary  and  
    when  your  applica7on  can  simply  restart  any  unfinished  jobs.  
     
    START_STICKY
    If  the  system  kills  the  service,  recreate  the  service  and  call  onStartCommand(),  but  do  
    not  redeliver  the  last  intent.  Instead,  the  system  calls  onStartCommand()  with  a  null  
    intent,  unless  there  were  pending  intents  to  start  the  service,  in  which  case,  those  intents  
    are  delivered.  This  is  suitable  for  media  players  (or  similar  services)  that  are  not  execu7ng  
    commands,  but  running  indefinitely  and  wai7ng  for  a  job.  
     
    START_REDELIVER_INTENT
    If  the  system  kills  the  service,  recreate  the  service  and  call  onStartCommand()  with  the  
    last  intent  that  was  delivered  to  the  service.  Any  pending  intents  are  delivered  in  turn.  This  
    is  suitable  for  services  that  are  ac7vely  performing  a  job  that  should  be  immediately  
    resumed,  such  as  downloading  a  file.  
    

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15. Don’t  forget  it!!  
    15/36  
    

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16. Good  Prac7ce!  J  
    16/36  
    Leaving  a  service  running  when  it’s  not  needed  is    
    one  of  the  worst  memory-­‐management  mistakes    
    an  Android  app  can  make.    
     
    So  don’t  be  greedy  by  keeping  a  service  for  your  app  running.  
     
    Not  only  will  it  increase  the  risk  of  your  app  performing  poorly  due  to  RAM  
    constraints,  but  users  will  discover  such  misbehaving  apps  and  uninstall  them.    
     
    Managing  Your  App's  Memory  
    hkp://developer.android.com/training/ar7cles/memory.html  
    Use  services  sparingly  
    

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17. Example:  LocalService  /  1  Process  
    17/36  
    

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18. 18/36  
    

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19. Ac7vity  
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Syst.  
    Events  
    UI  
    Events  
    Service  
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Syst.  
    Events  
    Process   Process  
    Applica7on  /  APK  Package  
    Example:  RemoteService  /  2  Processes  
    19/36  
    “Remote”  in  this  example  means  that  the  Service  is  hosted  in  another  process.  
    

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20. Example:  RemoteService  /  2  Processes  
    20/36  
    

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21. Example:  RemoteService  /  2  Processes  
    21/36  
    

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22. Applica7on  /  APK  Package  
    22/36  
    Use  mul7ple  processes  
    An  advanced  technique  that  may  help  you  manage  your  app's  memory  is  
    dividing  components  of  your  app  into  mul7ple  processes.    
     
    An  example  of  when  mul7ple  processes  may  be  appropriate  is  when  building  
    a  music  player  that  plays  music  from  a  service  for  long  period  of  7me.  
    Managing  Your  App's  Memory  
    hkp://developer.android.com/training/ar7cles/memory.html  
    Good  Prac7ce!  J  
    

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23. Ac7vity  
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Syst.  
    Events  
    UI  
    Events  
    Service  
    Handler  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Process  
    Applica7on  /  APK  Package  
    Example:  Service  +  HandlerThread  /  1  Process  
    23/36  
    HandlerThread  inherits  from  Thread  and  encapsulates  a  Looper-­‐object.  
    Is  a  Thread  with  a  message  queue  and  processing  loop.  
    

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24. Don’t  forget  it!!  
    24/36  
    Example:  Service  +  HandlerThread  /  1  Process  
    

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25. 25/36  
    Example:  Service  +  HandlerThread  /  1  Process  
    

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26. Example:  Service  +  HandlerThread  /  1  Process  
    26/36  
    

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27. 27/36  
    

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28. Ac7vity  
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Syst.  
    Events  
    UI  
    Events  
    IntentService  
    Worker  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    Process  
    Applica7on  /  APK  Package  
    Example:  IntentService  /  1  Process  
    36/36  
    This  is  the  best  op#on  if  you  don't  require  that  your  service  
    handle  mul7ple  requests  simultaneously  
    

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29. Example.  IntentService  /  1  Process  
    29/36  
    You  never  have  to  call  stopSelf().    
    Stops  itself  when  it  runs  out  of  work.  
    

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30. Example.  IntentService  /  1  Process  
    30/36  
    

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31. 1)  When  to  use?  
    •  The  Service  can  be  used  in  tasks  with  no  UI,  but  shouldn't  be  too  long.  If  you  need  to  
    perform  long  tasks,  you  must  use  threads  within  Service  or  use  another  process.  
    •  The  IntentService  can  be  used  in  long  tasks  usually  with  no  communica7on  to  Main  
    Thread.  This  is  the  best  op7on  if  you  don't  require  that  your  service  handle  mul7ple  
    requests  simultaneously.  
    2)  Triggered  From  
    •  The  Service  may  be  triggered  from  any  thread.  
    •  The  IntentService  must  be  triggered  from  Main  Thread.  
     
    3)  Runs  On  
    •  The  Service  runs  in  background  but  it  runs  on  the  Main  Thread  of  the  applica7on.  
    •  The  IntentService  runs  on  a  separate  Worker  Thread.  
     
    4)  Limita#ons  /  Drawbacks  
    •  The  Service  may  block  the  Main  Thread  of  the  applica7on.  
    •  The  IntentService  cannot  run  tasks  in  parallel.  
     
    Service  vs  IntentService  
    31/36  
    

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32. There  are  several  ways  to  get  results  from  a  Service  back  to  an  invoking  Ac7vity:  
    •  Broadcast  Intents  
               This  requires  having  the  Ac7vity  register  a  BroadcastReceiver.  
    •  Messenger  object  
               This  object  can  send  messages  to  an  Ac7vity’s  Handler.  
    •  Pending  Intent  
               Using  a  Pending  Intent  to  trigger  a  call  to  Ac7vity’s  onActivityResult()!
     
     
    Another  approach  is  to  let  the  user  know  directly  about  the  work  that  was  
    completed.  To  do  that,  a  Service  can  raise  a  No#fica#on.  
    Communica7ng  from  Services  
    32/36  
    

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33. Process  
    Applica7on  /  APK  Package  
    33/36  
    Bound  Services  
    

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34. Ac7vity  
     
     
     
     
     
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    RemoteService  
    Process   Process  
    Applica7on  A  /  APK  Package  
    Example:  Remote  Bound  Services  
    34/36  
    RemoteBinder  
     
     
     
    getRandomNumber()  
    Applica7on  B  /  APK  Package  
    mBound  
    1.  Call  method  
    2.  Return  results  
    to  caller  
    Binder  IPC  
    Mechanism  
    We  need  interprocess  communica7on  (IPC)  
    

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35. Ac7vity  
     
     
     
     
     
    Main  
    Thread  
     
     
     
     
     
     
     
    Looper  
    Message  
    Queue  
    RemoteService  
    Process  
    Applica7on  A  /  APK  Package  
    Example:  Locally  Bound  Services  
    35/36  
    RemoteBinder  
     
     
     
    getRandomNumber()  
    mBound  
    1.  Call  method  
    2.  Return  results  
    to  caller  
     Because  the  service  runs  in  the  same  process  as  its  clients,    
    we  don't  need  to  deal  with  IPC  
    

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36. José  Juan  Sánchez  Hernández  
    @josejuansanchez  
    

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