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Ch3 creating application and activities

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  • 1. Ch3. CreatingApplication & Activities Browny 06, May, 2011
  • 2. Application Building Blocks(1/5)• Activities ‣ Ac#vi#es  use  Views  to  form  graphical  user   interfaces  that  display  informa#on  and  response  to   user  ac#ons ‣ 例:一個  Email  程式,可能包含三個  ac#vi#es  (1) 郵件列表的ac#vity  (2)顯示郵件內容的ac#vity  (3) 寫新郵件或回覆郵件的ac#vity• Services ‣ Run  in  the  background,  upda#ng  your  data  sources   and  visible  Ac#vi#es  and  triggering  No#fica#ons
  • 3. Application Building Blocks(2/5)• Intents (An inter-application message- passing framework) ‣ Intent  綁定一次操作,它負責攜帶這次操作所 需要的資料以及操作的類型等• Content Providers (Sharable data stores) ‣ 在  Android  中,每個應用程式都是用自己的   user  ID  及在自己的  process  中執行。這樣做的 好處是,可以保護系統及應用程式,避免被 其他不正常的應用程式所影響。
  • 4. Application Building Blocks(3/5)• Content Providers (Sharable data stores) ‣ 例如:Contacts  應用程式內存了使用者聯絡 人資料。當你在  Email  這個應用程式,要填寫 收信人時,希望去讀取  Contacts  內的聯絡人 資料 ‣ 為瞭解決應用程式間,彼此要分享資料的需 求,Android  提供了  ContentProvider  這個機制
  • 5. Application Building Blocks(4/5)• Broadcast Receivers (Listen for broadcast intents that match specific filter criteria) ‣ 當開發人員希望應用程式來對外部的事件做 一些處理時,可以使用Broadcast  Intent   Receiver。例如:當電話響時,或是網路資料 可以使用時,或是時間到了午夜時
  • 6. Application Building Blocks(5/5)• Widgets ‣ Visual  applica#on  components  that  can  be   added  to  the  home  scree• Notifications ‣ No#fica#ons  let  you  signal  users  without   stealing  focus  or  interrup#ng  their  current   Ac#vi#es
  • 7. Application Manifest• 在 Android 執行一個應用之前,必須先知道該 應用有哪些元件 (Activity, Service, 等等),這些 元件的描述被放在 AndroidManifest.xml 檔案中• AndroidManifest.xml 會連同執行碼與相關資源 等一同打包到 .apk 專案檔中http://developer.android.com/guide/topics/manifest/manifest-intro.html• 除了宣告元件之外,使用 intent filter 和 permissions 決定元件彼此互動的方式、定義給 外部用的函式庫名稱,並且設定權限機制等等
  • 8. Application Life Cycle• Application 本身對自己的 life cycles 沒有 太多控制權,application components 聽 取 application states 的改變來做反應,尤 其隨時要對無預警的終止做準備• Each Android application runs in its own process, each of which is running a separate instance of Dalvik• 記憶體和行程完全由 run-time 管理
  • 9. Application Priority and Process States(1/2)• An application’s priority is equal to its highest-priority component• If 2 applications have the same priority, the process that has been at a lower priority longest will be killed first• Process priority is also affected by interprocess dependencies ‣ If  an  applica#on  has  a  dependency  on  a  Service  or  Content   Provider  supplied  by  a  second  applica#on,  the  secondary   applica#on  will  have  at  least  as  high  a  priority  as  the  applica#on  it   supports• All Android applications will remain running and in memory until the system needs resources for other applications
  • 10. Application Priority and Process States(2/2) Externalizing Resources ! 59 • Active ProcessT he following list details each of the application states Critical Priorityshown in Figure 3-3, explaining in  an  “ac#ve”  state ‣ components comprising it: is determinedby the application Ac#vi#es   how the state 1. Active Process " Active‣ Broadcast  Receivers   processes processes A ctive (foreground) High Priority have application components interacting   execu#ng  onRe  c  e  i  v  e with 2. Visible Process the user. T hese are the processes A ndroid is try- ing to keepevent  handlers responsive by reclaiming resources. T here are generally very few of these processes, 3. Started Service Process ‣ Services   only as a last resort. and they will be killed execu#ng  onStart,   A ctive processes include:or  onDestroy   onCreate,   Low Priority A ctivities in andlers state; that is, event  h an ‘‘active’’ 4. Background Process " those in the foreground responding to ‣ user events. YServices  that  have   Running   ou will explore A ctiv- 5. Empty Process itybeen  in agged  detailun  in  the   states fl greater to  r later in this foreground chapter. FIGURE 3-3 . " Broadcast Receivers executing onRe c e i v e event handlers. " Services executing onS t a r t , onC r e a t e , or onDe s t r o y event handlers.
  • 11. Externalize Resources(1/2)• Good practice to keep non-code resources like images and string constants external to your code• 9 primary resource types have different folders: simple values, Drawables, layouts, animations, styles, menus, searchables, XML, and raw resources
  • 12. Externalize Resources(2/2)• These resources will be compiled as efficiently as possible and included in your application package• This process also generates an R class file that contains references to each of the resources you include in your project
  • 13. Using Resources(1/2)• You access resources in code using the static R class• The R class contains static subclasses for each of the resource types for which you’ve defined at least one resource• Each of the subclasses within R exposes its associated resources as variables (直接指向 resource table), with the variable names matching the resource identifiers ‣ R.string.app_name,  R.drawable.icon
  • 14. Using Resources(2/2)• 當需要資源本身的實體,必須使用 getResources() 把 resource table 抽取出來 成為一個 Resource 類的實體• Resource 類當中包含了針對每種可獲取 資源型別的 getters 方法 (將欲獲取的 resource ID 當做參數傳入 getter 方法)
  • 15. cess yourbe static. UseResources instance.s method on your application context, as s application’s the g e t Re s ou r c e Re s ou r caccess yourr application’sou r c e s ( ) ; to e s myRe s ou c e s = g e t Re s Resources instance.Re s ou r c e s class includes getters for each ofcthe available s ou r c e s types and generally wo Re s ou r c e s myRe s ou r e s = g e t Re resource ( ) ;ng in the resource I D you’d like an instance of. T he following code snippet shows an exa the helperhe Re s ou to e s class selection of resource values. of the available resource t T methods r c return a includes getters for each passing in the resource I D you’d like an instance of. T he following code Re s ou r c e s myRe s ou r c e s = g e t Re s ou r c e s ( ) ; using the helper methods to return a selection of resource values. Ch a r Se qu e n c e s t y l e dT e x t = myRe s ou r c e s . g e t T e x t ( R . s t r i ng . s t op_me s s a g e ) ; D r awa b l e i c onRe smyRec e s r myRegseou r awa b l=e (g e d Re s oul rec e pp_ i;c on ) ; = ou r s ou c e s . t D r c e s R . t r awa b . a s ( ) i n t op a qu eB l uCh = rmyRe s e n c c e ss. tgy lt e dTo rx(tR .= omyReopou r c _b l. u ee) t;T e x t ( R . s t r i ng e a Se qu ou r e e Co l e c l o r . s a qu e e s g D r awa b l e i c on = myRe s ou r c e s . g e t D r awa b l e ( R . d r awa b l e . a pp f l o a t bo r d e r W i d t h = myRe s ou r c e s . g e t D i me n s i on ( R . d i me n . s t a nd a r d_bo r d e r ) ; i n t op a qu eB l u e = myRe s ou r c e s . g e t Co l o r ( R . c o l o r . op a qu e _b An i ma t i on t r a nOu t ; t r a nOu t = An i ma t i onU t i l s . l o a dAn i ma t i on ( t h i s , R . a n i m . s p i n_ s h r i n k _ f a d e ) ; f l o a t bo r d e r W i d t h = myRe s ou r c e s . g e t D i me n s i on ( R . d i me n . s S t r i ng [ ] s t r i ngA r r a y ; s t r i ngA r r a y =An i mastouon e s .r g e t S t tr ;i ngA r r a y ( R . a r r a y . s t r i ng_ a r r a y ) ; myRe i r c t a nOu t r a nOu t = An i ma t i onU t i l s . l o a dAn i ma t i on ( t h i s , R . a n i m . s p i n t [ ] i n t A r r a y = myRe s ou r c e s . g e t I n t A r r a y ( R . a r r a y . i n t e g e r _ a r r a y ) ; S t r i ng [ ] s t r i ngA r r a y ;e-by-frame animatedt resourcesaare =inflatedsinto c e si ma e it onRe isngAc ersa. yY ou a r r areturnr thn s r i ngA r r y myRe ou r An t .g St r ou r r (R . can y . s t i g e t D r awa b l e and casting the return value, as shown here:
  • 16. Referencing Resources within Resources(1/2)• You can also use resource references as attribute values in other XML resources• To reference one resource from another use @ notation ‣ attribute= "@[packagename:] resourcetype/ resourceidentifier"
  • 17. Referencing Resources within Resources(2/2)
  • 18. Using System Resources• Use the native Android resource classes available from android.R, rather than the application-specific R class ‣ CharSequence  hPpError  =  getString(android.R.string.hPpErrorBadUrl);• To access system resources in XML specify android as the package name
  • 19. 70 Referring to StylesAND Athe Current ! CHAPTER 3 CREATING APPLIC ATIO NS in CTIVITIES Theme • Referring to Styles in the Current Theme to ensure Using themes is an excellent way consistency for your application’s UI Using themes is an excellent way to ensure consistency for your applicatio define each style, A ndroid provides a shortcut to let you use styles from the • use ?android: rather than @ as a prefix to T o do this you use ? a nd r o i d : rather than @ as a prefix to the resource you the resource you want to use example shows a snippet of the preceding code but uses the current theme external resource. <Ed i t T e x t a nd r o i d : i d= " @+ i d / my Ed i t T e x t " a nd r o i d : l a y ou t _w i d t h= " f i l l _p a r e n t " a nd r o i d : l a y ou t _h e i gh t = " w r a p_ c on t e n t " a nd r o i d : t e x t = " @s t r i ng / s t op_me s s a g e " and r o i d : t e x t Co l o r = " ?and r o i d : t e x t Co l o r " /> T his technique lets you create styles that will change if the current theme ch
  • 20. Creating Resources for Different Languages and Hardware(1/2)• Dynamic resource-selection mechanism• Using a parallel directory structure within the res folder. A hyphen (-) is used to separate qualifiers that specify the conditions you’re providing alternatives for
  • 21. Creating Resources for Different Languages and Hardware(2/2)• list of qualifiers ‣ Mobile  Country  Code/Mobile  Network  Code ‣ Language  and  Region ‣ Screen  Size ‣ Screen  Width/Length ‣ Screen  Orienta#on they must be used in the order ‣ Screen  Pixel  Density ‣ Touch  Screen  Type ‣ Keyboard  Availability ‣ Keyboard  Input  Type ‣ UI  Naviga#on  Type
  • 22. Runtime Configuration Changes(1/3)• Android handles runtime changes to the language, location, and hardware by terminating and restarting each application and reloading the resource values• This default behavior isn’t always convenient or desirable• To have an Activity listen for runtime configuration changes, add an android:conf igChanges attribute to its manifest node
  • 23. Runtime Configuration Changes(2/3)• Adding an android:configChanges attribute suppresses the restart for the specified configuration changes, instead triggering the onConfigurationChanged method in the Activity• Configuration changes you can specify ‣ Orienta#on,  keyboardHidden,  fontScale,  locale,   keyboard,  touchscreen,  naviga#on ‣ You  can  select  mul#ple  events  you  wish  to  handle   yourself  by  separa#ng  the  values  with  a  pipe  (|).
  • 24. Runtime Configuration Changes(3/3) Handling configuration changes in code
  • 25. Android Application Class(1/2)• Extending Application class enables you to ‣ Maintain  applica#on  states ‣ Transfer  objects  between  applica#on   components ‣ Manage  and  maintain  resources  used  by  several   applica#on  components
  • 26. Android Application Class(2/2)• When your Application implementation is registered in the manifest, it will be instantiated when your application process is created
  • 27. Skeleton Application Class
  • 28. Application Life Cycle Events• onCreate ‣ Override  this  method  to  ini#alize  your  applica#on  singleton   and  create  and  ini#alize  any  applica#on  state  variables  or   shared  resources• onTerminate ‣ There  is  no  guarantee  of  this  method  handler’s  being  called• onLowMemory• onConfigurationChanged ‣ Unlike  with  Ac#vi#es,  your  applica#on  object  is  not  killed   and  restarted  for  configura#on  changes
  • 29. Android Activities(1/3)• Each Activity represents a screen that an application can present to its users
  • 30. Android Activities(2/3)• An empty Activity isn’t particularly useful, so the first thing you’ll want to do is create the user interface with Views and layouts• To assign a user interface to an Activity, call setContent View from the onCreate method of your Activity
  • 31. Android Activities(3/3)• In order to use an Activity in your application you need to register it in the manifest• For an Activity to be available from the main application launcher it must include an Intent Filter listening for the MAIN action and the LAUNCHER category
  • 32. The Activity Life Cycle• Run time handles the termination and management of an Activity’s process• Activity States <=互相影響=> Application Priority
  • 33. Activity Stacks(1/2)
  • 34. Activity Stacks(2/2)• The Activity state is determined by its position on the Activity stack• An application’s priority is influenced by its highest- priority Activity• When the Android memory manager is deciding which application to terminate to free resources, it uses this stack to determine the priority of applications based on their Activities.
  • 35. Activity States• Active• Paused ‣ Be  visible  but  will  not  have  focus.  This  state  is  reached  if  a   transparent  or  non-­‐full-­‐screen  Ac#vity  is  ac#ve  in  front  of  it• Stopped ‣ When  an  Ac#vity  isn’t  visible,  it  ‘‘stops.’’  It  is  now  a   candidate  for  termina#on  when  the  system  requires   memory  elsewhere• Inactive ‣ Ader  an  Ac#vity  has  been  killed,  and  before  it’s  been   launched,  it’s  inac#ve
  • 36. Monitoring State Changes• Android provides a series of event handlers that are fired when an Activity transitions through its full, visible, and active lifetimes
  • 37. Thank you :)

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