Activities, Fragments and Intents

Transcription

1 Mobile App Development

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4 Manifest file Outline AndroidManifest.xml XML file Contains name of the application and a default package, Sets up the various permissions required by this application, Defines the application-wide parameters, Defines the startup Activity for the application.

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6 res/values/strings.xml You can use file string.xml to keep global constants such as name of the app, communicates, headers etc. 1 < s t r i n g name= a b o u t t i t l e >About Android </ s t r i n g > 2 < s t r i n g name= a b o u t t e x t >\ 3 Android a l l o w s you to use xml to d e s c r i b e GUI and to s t o r e v a l u e s. 4 You can a s l o use <i >HTML</i > t a g s i n t h e r e. 5 </ s t r i n g >

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8 res/values/colors.xml Outline You can define custom colors that can be used in definitions of layout and layout elements 1 <r e s o u r c e s > 2 <c o l o r name= background >#3500 f f f f </c o l o r > 3 </ r e s o u r c e s >

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10 How? Outline Declarative Statically (off-line) declare the interface using XML-based language. It is similar to building XHTML web page.

11 How? Outline Declarative Statically (off-line) declare the interface using XML-based language. It is similar to building XHTML web page. Procedural Simply means in code. You write Java code to create and manipulate all the user interface objects called Views.

12 How? Outline Declarative Statically (off-line) declare the interface using XML-based language. It is similar to building XHTML web page. Procedural Simply means in code. You write Java code to create and manipulate all the user interface objects called Views. Mixed Android allows you also to mix both methods. You can build a skeleton declaratively and fill in required elements during the execution. This approach allows for flexibility minimizing coding.

13 Advice from Google Outline Google s advice is to use declarative XML as much as possible. The XML code is often shorter and easier to understand than the corresponding Java code, and its less likely to change in future versions.

14 Why XML? Isn t it ineffective? Although you see XML when writing your program, the Eclipse plug-in invokes the Android resource compiler, aapt, to preprocess the XML into a compressed binary format. It is this format, not the original XML text, that is stored on the device.

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16 Basic elements Outline View An object that knows how to draw itself to the screen. ViewGroup Views that can contain or group other Views. Layout Gives Android hints about how youd like to see the Views arranged.

17 Layout View 1 View 2 ViewGroup View 3 View 4 Figure: A concept of layouts, groups and views

18 Layout Outline Layout is: a container for one or more child objects a behaviour to position them on the screen within the rectangle of the parent object

19 Layout Outline Commonly used layouts FrameLayout all children start at the top left of the screen LinearLayout children in a single column or row RelativeLayout children in relation to each other or to the parent TableLayout children in rows and columns, similar to an HTML table

20 Vertical vs. Horizontal You can declare layouts fitted for specific position of the device Horizontal res/layout/main.xml Can contain e.g. ListLayout Vertical res/layout-land/main.xml Can contain TableLayout nested in ListLayout to make better use of the space

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23 Design Principles Design Principles Enchant Me Simplify My Life Make Me Amazing Source: get-started/principles.html

24 Action Bars and other... Design Principles Action Bar 1 Home button that takes your user to Home Screen/Activity 2 View control (e.g. in Calendar it may be option to show Year/Month/Week/Day) 3 Action buttons such as Search, Zoom etc 4 Overflow actions...

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26 Design Principles

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28 Activity Outline What is it? An activity is a user interface screen. Applications can define one or more activities to handle different phases of the program. Declaration In AndroidManifest.xml Definition In Java as an extension of Activity class

29 Declaration Outline 1 <a p p l i c a t i o n... > < a c t i v i t y a n d r o i d : name=. S u n C a l c u l a t o r A c t i v i t y 4 a n d r o i d : l a b e s t r i n g / app name > 5 <i n t e n t f i l t e r > 6 <a c t i o n a n d r o i d : name= a n d r o i d. i n t e n t. a c t i o n. MAIN /> 7 <c a t e g o r y a n d r o i d : name= a n d r o i d. i n t e n t. c a t e g o r y. LAUNCHER /> 8 </ i n t e n t f i l t e r > 9 </ a c t i v i t y > </ a p p l i c a t i o n >

30 Definition Outline 1 p u b l i c c l a s s S u n C a l c u l a t o r A c t i v i t y e x t e n d s A c t i v i t y { 2 3 / C a l l e d when t h e a c t i v i t y i s f i r s t c r e a t e d. / O v e r r i d e 5 p u b l i c v o i d o n C r e a t e ( Bundle s a v e d I n s t a n c e S t a t e ) { 6 s u p e r. o n C r e a t e ( s a v e d I n s t a n c e S t a t e ) ; 7 8 // Here you i n i t i a l i z e, b u i l d t h e UI e l e m e n t s e t c 9 10 } // then you can add v a r i o u s c a l l b a c k f u n c t i o n s to h a n d l e e v e n t s 13 }

31 Activity main app component

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33 Intent Outline What is it? An intent is a mechanism for describing a specific action, such as pick a photo, phone home, or show map How is it done? An instance of Intent class is created and parameters such as action, category and data are set.

34 Calling specific activity 1 2 I n t e n t m y I n t e n t = new I n t e n t ( t h i s, C a l l e d A c t i v i t y. c l a s s ) ; 3 s t a r t A c t i v i t y ( m y I n t e n t ) ; 4 5 // o r s t a r t A c t i v i t y F o r R e s u l t ( m y I n t e n t rescode ) ; 6 // i f you want to g e t a r e s u l t

35 Component based architecture Ask others to do it for you Android allows you to call activities and services from other apps! You can send a request e.g. to open a photo or show a map and (if there is an app accepting such call) it will be served. If multiple apps can handle it then user can choose who (which app) will be used.

36 Calling activity based on action/category 1 2 I n t e n t m y I n t e n t = new I n t e n t ( 3 a n d r o i d. c o n t e n t. I n t e n t. ACTION VIEW, 4 // White house l o c a t i o n 5 U r i. p a r s e ( geo : , ) 6 ) ; 7 8 s t a r t A c t i v i t y ( m y I n t e n t ) ; 9 10 // o r s t a r t A c t i v i t y F o r R e s u l t ( m y I n t e n t rescode ) ; 11 // i f you want to g e t a r e s u l t

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38 Fragment Encapsulated, reusable component with own lifecycle and UI that can be used to build activity. It is tightly bound to the Activity into which it is placed. They can be reused in various activities.

39 Fragments in Android Fragments were introduced as a part of Android 3.0 Honeycomb (API level 11). Recquired Your activity has to extend FragmentActivity public class MyActivity extends FragmentActivity

40 Create a Fragment Class Extend Fragment class Create layout file with view hierarchy (optionally) If your fragment requires UI override oncreateview handler to inflate and return the view hierarchy (from layout file or automatically).

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42 Created Fragment.onAttach Fragment.onDeatach Fragment.onCreate Fragment.onDestroy Fragment.onCreateView Fragment.onDestroyView Fragment.onActivityCreated.

43 .. Visible Fragment.onStart Fragment.onStop Active Fragment.onResume Fragment.onPause

44 Fragment-specific Lifecycle Events Attach/Deattach Start and End of the life-cycle Create/Destroy Start and End of the created lifetime Create/Destroy UI oncreateview should be used to initialize fragment s UI

45 Fragment States Outline State A state of the fragment is closely related to the corresponding Activity state and it s transitions are related to Activity s transitions.

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47 Fragment Manager Outline FragmentManager is used to manage fragments that the Activity contains. It provides the methods to perform fragment transaction to add, remove and replace fragments.

48 Layout file Simplest way to add a fragment to an activity is to add <fragment> tag to the layout. 1 <f ragment 2 a n d r o i d : name= com. paad. w e a t h e r s t a t i o n. D e t a i l s F r a g m e n t 3 a n d r o i d : i d / fragment1 4 a n d r o i d : l a y o u t w i d t h= m a t c h p a r e n t 5 a n d r o i d : l a y o u t h e i g h t= m a t c h p a r e n t 6 a n d r o i d : l a y o u t w e i g h t= 3 7 />

49 Fragment transaction Fragment Transactions can be used to add, remove, and replace fragments within the activity at runtime. 1 F r a g m e n t T r a n s a c t i o n t = fragmentmanager. b e g i n T r a n s a c t i o n ( ) ; 2 // to add 3 t. add (R. i d. u i c o n t a i n e r, new MyFragment ( ) ) ; 4 5 // to remove 6 Fragment f = fragmentmanager. f i n d F r a g m e n t B y I d (R. i d. myfragment ) ; 7 t. remove ( f ) ; 8 9 // to r e p l a c e 10 t. r e p l a c e (R. i d. myfragment, new MyFragment ( ) ) ; t. commit ( ) ;

50 Back Stack If you use fragments to display different screens within the same activity, user will expect that back button will revers the Fragment Transaction effects. You can fulfill this expectation by adding the transaction to the back stack fragmenttransaction.addtobackstack(tag).

51 Built-in Fragment Classes DialogFragment floating dialog ListFragment wrapper class featuring ListView WebViewFragment wrapper class featuring WebView

52 Summary Outline Fragment should encapsulate a functionality and be fairy independent Fragment can have own UI (but it s possible to create one without it) Fragments can be dynamically added, removed and replaced Fragments can communicate through Activity

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