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AperiodicalaboutbestpracticesandadvancedtechniquesforiOSandOSXdevelopment.

Android101foriOSDevelopers

Issue#11Android,April2014

ByStephenBarnes

Asthemobilesoftwareindustryevolves,itisbecomingincreasinglyimpracticaltotargetonlyiOSforamobileproduct.Androidmarketshareisapproaching80percentforsmartphones,1andthenumberofpotentialusersthatitcanbringtoaproductcanhardlybeignored.

Inthisarticle,IwillintroducethecoreconceptsofAndroiddevelopmentwithinthecontextofiOSdevelopment.AndroidandiOSworkonsimilarproblemsets,buttheyapproachmanyoftheseproblemsindifferentways.Throughoutthearticle,Iwillbeusingacompanionproject(availableonGitHub)toillustratehowtoaccomplishthesametaskswhendevelopingforbothplatforms.

InadditiontoaworkingknowledgeofiOSdevelopment,IassumethatyouhaveaworkingknowledgeofJavaandareabletoinstallandusetheAndroidDevelopmentTools.Furthermore,ifyouarenewtoAndroiddevelopment,readingthroughthetutorialbyGoogleaboutbuildingyourfirstappcouldbeveryhelpful.

ABriefWordonUIDesign

ThisarticlewillnotdelvedeeplyintotheuserexperienceanddesignpatterndifferencesbetweeniOSandAndroid.However,itwouldbebeneficialtounderstandsomeofthekeyUIparadigmsinuseonAndroidtoday:theactionbar,theoverflowmenu,thebackbutton,theshareaction,andmore.IfyouareseriouslyconsideringAndroiddevelopment,IhighlyrecommendinglookingintotheNexus5fromtheGooglePlayStore.Makeityourfulltimedeviceforaweekandforceyourselftotrytheoperatingsystemtoitsfullestextent.Adeveloperwhodoesntknowthekeyusepatternsofhisorheroperatingsystemisaliabilitytotheproduct.

LanguageApplicationStructure

Java

TherearemanydifferencesbetweenObjectiveCandJava,andwhileitmaybetemptingtobringsomeofObjectiveCsstylingintoJava,itcanleadtoacodebasethatheavilyclasheswiththeprimaryframeworkthatdrivesit.Inbrief,hereareafewgotchastowatchfor:

LeaveclassprefixesathomeonObjectiveC.Javahasactualnamespacingandpackagemanagement,sothereisnoneedforclassprefixeshere.Instancevariablesareprefixedwithm,not_.

TakeadvantageofJavaDoctowritemethodandclassdescriptionsforasmuchofyourcodeaspossible.Itwillmakeyourlifeandthelivesofothersbetter.Nullcheck!ObjectiveCgracefullyhandlesmessagesendingtonilobjects,butJavadoesnot.Saygoodbyetoproperties.Ifyouwantsettersandgetters,youhavetoremembertoactuallycreateagetVariableName()methodandcallitexplicitly.Referencingthis.objectwillnotcallyourcustomgetter.Youmustusethis.getObject.Similarly,prefixmethodnameswithgetandsettoindicategettersandsetters.Javamethodsaretypicallywrittenasactionsorqueries,suchasgetCell(),insteadofcellForRowAtIndexPath:.

ProjectStructure

Androidapplicationsareprimarilybrokenintotwosections,thefirstofwhichistheJavasourcecode.ThesourcecodeisstructuredviatheJavapackagehierarchy,anditcanbestructuredasyouplease.However,acommonpracticeistousetoplevelcategoriesforactivities,fragments,views,adapters,anddata(modelsandmanagers).

Thesecondmajorsectionistheresfolder,shortforresourcefolder.Theresfolderisacollectionofimages,XMLlayoutfiles,andXMLvaluefilesthatmakeupthebulkofthenoncodeassets.OniOS,imagesareeither@2xornot,butonAndroidthereareanumberofscreendensityfolderstoconsider.2Androidusesfolderstoarrangeimages,strings,andothervaluesforscreendensity.TheresfolderalsocontainsXMLlayoutfilesthatcanbethoughtofasxibfiles.Lastly,thereareotherXMLfilesthatstoreresourcesforstring,integer,andstyleresources.

OnelastcorrelationinprojectstructureistheAndroidManifest.xmlfile.ThisfileistheequivalentoftheProjectInfo.plistfileoniOS,anditstoresinformationforactivities,applicationnames,andsetIntents3(systemlevelevents)thattheapplicationcanhandle.FormoreinformationaboutIntents,keeponreading,orheadovertotheIntentsarticle.

Activities

ActivitiesarethebasicvisualunitofanAndroidapp,justasUIViewControllersarethebasicvisualcomponentoniOS.InsteadofaUINavigationController,theAndroidOSkeepsanactivitystackthatitmanages.Whenanappislaunched,theOSpushestheappsmainactivityontothestack.Notethatyoucanlaunchotherapps'activitiesandhavethemplacedontothestack.Bydefault,thebackbuttononAndroidpopsfromtheOSactivitystack,sowhenauserpressesback,heorshecangothroughmultipleappsthathavebeenlaunched.

ActivitiescanalsoinitializeotheractivitieswithIntentsthatcontainextradata.StartingActivitieswithIntentsissomewhatsimilartocreatinganewUIViewControllerwithacustominitmethod.BecausethemostcommonwaytolaunchnewactivitiesistocreateanIntentwithdata,agreatwaytoexposecustominitializersonAndroidistocreatestaticIntentgettermethods.Activitiescanalsoreturnresultswhenfinished(goodbyemodaldelegates!)byplacingextradataonanIntentwhentheactivityisfinished.

OnelargedifferencebetweenAndroidappsandiOSappsisthatanyactivitycanbeanentrancepointintoyourapplicationifitregisterscorrectlyintheAndroidManifestfile.SettinganIntentfilterintheAndroidManifest.xmlfileforamediaintentonanactivityeffectivelystatestotheOSthatthisactivityisabletobelaunchedasanentrypointwithmediadatainsideoftheIntent.Agoodexamplemightbeaphotoeditingactivitythatopensaphoto,modifiesit,andreturnsthemodifiedimagewhentheactivityfinishes.

Asasidenote,modelobjectsmustimplementtheParcelableinterfaceifyouwanttosendthembetweenactivitiesandfragments.ImplementingtheParcelableinterfaceissimilartoconformingtotheprotocoloniOS.AlsonotethatParcelableobjectsareabletobestoredinanactivitysorfragmentssavedInstanceState,inordertomoreeasilyrestoretheirstatesaftertheyhavebeendestroyed.

Letsnextlookatoneactivitylaunchinganotheractivity,andalsorespondingtowhenthesecondactivityfinishes.

LaunchingAnotherActivityforaResult

//ArequestcodeisauniquevalueforreturningactivitiesprivatestaticfinalintREQUEST_CODE_NEXT_ACTIVITY=1234;

protectedvoidstartNextActivity(){//Intentsneedacontext,sogivethiscurrentactivityasthecontextIntentnextActivityIntent=newIntent(this,NextActivity.class);startActivityForResult(nextActivityResult,REQUEST_CODE_NEXT_ACTIVITY);}

@OverrideprotectedvoidonActivityResult(intrequestCode,intresultCode,Intentdata){switch(requestCode){caseREQUEST_CODE_NEXT_ACTIVITY:if(resultCode==RESULT_OK){//ThismeansourActivityreturnedsuccessfully.Fornow,Toastthistext.

//Thisjustcreatesasimplepopupmessageonthescreen.Toast.makeText(this,"ResultOK!",Toast.LENGTH_SHORT).show();



Toast.makeText(this,"ResultOK!",Toast.LENGTH_SHORT).show();}return;}super.onActivityResult(requestCode,resultCode,data);}

ReturningaResultonActivityFinish()

publicstaticfinalStringactivityResultString="activityResultString";

/**Oncompletion,placetheobjectIDintheintentandfinishwithOK.*@paramreturnObjectthatwasprocessed*/privatevoidonActivityResult(ObjectreturnObject){Intentdata=newIntent();if(returnObject!=null){data.putExtra(activityResultString,returnObject.uniqueId);}

setResult(RESULT_OK,data);finish();}

Fragments

TheFragmentconceptisuniquetoAndroidandcamearoundsomewhatrecentlyinAndroid3.0.Fragmentsareminicontrollersthatcanbeinstantiatedtofillactivities.Theystorestateinformationandmaycontainviewlogic,buttheremaybemultiplefragmentsonthescreenatthesametimeputtingtheactivityinafragmentcontrollerrole.Alsonotethatfragmentsdonothavetheirowncontextsandtheyrelyheavilyonactivitiesfortheirconnectiontotheapplicationsstate.

Tabletsareagreatfragmentusecaseexample:youcanplacealistfragmentontheleftandadetailfragmentontheright.4FragmentsallowyoutobreakupyourUIandcontrollerlogicintosmaller,reusablechunks.Butbeware!Thefragmentlifecycle,detailedbelow,ismorenuanced.

FragmentsarethenewwayofstructuringappsonAndroid,justlikeUICollectionViewisthenewwayofstructuringlistdatainsteadofUITableviewforiOS.5Whileitisinitiallyeasiertoavoidusingfragmentsandinsteadusenothingbutactivities,youcouldregretthisdecisionlateron.Thatsaid,resisttheurgetogiveuponactivitiesentirelybyswappingfragmentsonasingleactivitythiscanleaveyouinabindwhenwantingtotakeadvantageofintentsandusingmultiplefragmentsonthesameactivity.

LetslookatasampleUITableViewControllerandasampleListFragmentthatshowalistofpredictiontimesforasubwaytrip,courtesyoftheMBTA.

TableViewControllerImplementation



@interfaceMBTASubwayTripTableTableViewController()

@property(assign,nonatomic)MBTATrip*trip;

@end

@implementationMBTASubwayTripTableTableViewController

(instancetype)initWithTrip:(MBTATrip*)trip{self=[superinitWithStyle:UITableViewStylePlain];if(self){_trip=trip;[selfsetTitle:trip.destination];}returnself;}

(void)viewDidLoad{[superviewDidLoad];

[self.tableViewregisterClass:[MBTAPredictionCellclass]forCellReuseIdentifier:[MBTAPredictionCellreuseId]];[self.tableViewregisterNib:[UINibnibWithNibName:NSStringFromClass([MBTATripHeaderViewclass])bundle:nil]forHeaderFooterViewReuseIdentifier:[MBTATripHeaderViewreuseId]];}

#pragmamarkUITableViewDataSource

(NSInteger)numberOfSectionsInTableView:(UITableView*)tableView{return1;}

(NSInteger)tableView:(UITableView*)tableViewnumberOfRowsInSection:(NSInteger)section{return[self.trip.predictionscount];}

#pragmamarkUITableViewDelegate

(CGFloat)tableView:(UITableView*)tableViewheightForHeaderInSection:(NSInteger)section{return[MBTATripHeaderViewheightWithTrip:self.trip];}

(UIView*)tableView:(UITableView*)tableViewviewForHeaderInSection:(NSInteger)section{MBTATripHeaderView*headerView=[self.tableViewdequeueReusableHeaderFooterViewWithIdentifier:[MBTATripHeaderViewreuseId]];[headerViewsetFromTrip:self.trip];



[headerViewsetFromTrip:self.trip];returnheaderView;}

(UITableViewCell*)tableView:(UITableView*)tableViewcellForRowAtIndexPath:(NSIndexPath*)indexPath{UITableViewCell*cell=[tableViewdequeueReusableCellWithIdentifier:[MBTAPredictionCellreuseId]forIndexPath:indexPath];

MBTAPrediction*prediction=[self.trip.predictionsobjectAtIndex:indexPath.row];[(MBTAPredictionCell*)cellsetFromPrediction:prediction];

returncell;}

(BOOL)tableView:(UITableView*)tableViewcanEditRowAtIndexPath:(NSIndexPath*)indexPath{returnNO;}

(void)tableView:(UITableView*)tableViewdidSelectRowAtIndexPath:(NSIndexPath*)indexPath{[tableViewdeselectRowAtIndexPath:indexPathanimated:YES];}

@end

ListFragmentImplementation

publicclassTripDetailFragmentextendsListFragment{

/***TheconfigurationflagsfortheTripDetailFragment.*/publicstaticfinalclassTripDetailFragmentState{publicstaticfinalStringKEY_FRAGMENT_TRIP_DETAIL="KEY_FRAGMENT_TRIP_DETAIL";}

protectedTripmTrip;

/***Usethisfactorymethodtocreateanewinstanceof

*thisfragmentusingtheprovidedparameters.**@paramtripthetriptoshowdetails*@returnAnewinstanceoffragmentTripDetailFragment.*/publicstaticTripDetailFragmentnewInstance(Triptrip){TripDetailFragmentfragment=newTripDetailFragment();



TripDetailFragmentfragment=newTripDetailFragment();Bundleargs=newBundle();args.putParcelable(TripDetailFragmentState.KEY_FRAGMENT_TRIP_DETAIL,trip);fragment.setArguments(args);returnfragment;}

publicTripDetailFragment(){}

@OverridepublicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,BundlesavedInstanceState){Prediction[]predictions=mTrip.predictions.toArray(newPrediction[mTrip.predictions.size()]);PredictionArrayAdapterpredictionArrayAdapter=newPredictionArrayAdapter(getActivity(),predictions);setListAdapter(predictionArrayAdapter);returnsuper.onCreateView(inflater,container,savedInstanceState);}

@OverridepublicvoidonViewCreated(Viewview,BundlesavedInstanceState){super.onViewCreated(view,savedInstanceState);TripDetailsViewheaderView=newTripDetailsView(getActivity());headerView.updateFromTripObject(mTrip);getListView().addHeaderView(headerView);}}

Inthenextsection,letsdeciphersomeoftheuniqueAndroidcomponents.

CommonAndroidComponents

ListViewsandAdapters

ListViewsaretheclosestapproximationtoUITableViewonAndroid,andtheyareoneofthemostcommoncomponentsthatyouwilluse.JustlikeUITableViewhasahelperviewcontroller,UITableViewController,ListViewalsohasahelperactivity,ListActivity,andahelperfragment,ListFragment.SimilartoUITableViewController,thesehelperstakecareofthelayout(similartothexib)foryouandprovideconveniencemethodsformanagingadapters,whichwelldiscussbelow.OurexampleaboveusesaListFragmenttodisplaydatafromalistofPredictionmodelobjects,similartohowthetableviewsdatasourceusesanarrayofPredictionmodelobjectstopopulatetheUITableView.

Speakingofdatasources,onAndroidwedonthavedatasourcesanddelegatesforListView.Instead,wehaveadapters.Adapterscomeinmanyforms,buttheirprimarygoalissimilartoadatasourceandtableviewdelegateallinone.AdapterstakedataandadaptittopopulateaListViewbyinstantiatingviewstheListViewwilldisplay.Letshavealookatthearrayadapterusedabove:

publicclassPredictionArrayAdapterextendsArrayAdapter{

intLAYOUT_RESOURCE_ID=R.layout.view_three_item_list_view;

publicPredictionArrayAdapter(Contextcontext){super(context,R.layout.view_three_item_list_view);}

publicPredictionArrayAdapter(Contextcontext,Prediction[]objects){super(context,R.layout.view_three_item_list_view,objects);}

@OverridepublicViewgetView(intposition,ViewconvertView,ViewGroupparent){Predictionprediction=this.getItem(position);ViewinflatedView=convertView;if(convertView==null){LayoutInflaterinflater=(LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);inflatedView=inflater.inflate(LAYOUT_RESOURCE_ID,parent,false);}

TextViewstopNameTextView=(TextView)inflatedView.findViewById(R.id.view_three_item_list_view_left_text_view);TextViewmiddleTextView=(TextView)inflatedView.findViewById(R.id.view_three_item_list_view_middle_text_view);TextViewstopSecondsTextView=(TextView)inflatedView.findViewById(R.id.view_three_item_list_view_right_text_view);

stopNameTextView.setText(prediction.stopName);middleTextView.setText("");stopSecondsTextView.setText(prediction.stopSeconds.toString());

returninflatedView;}}

YoullnotethattheadapterhasanimportantmethodnamedgetView,whichisverysimilartocellForRowAtIndexPath:.Anothersimilarityyoullnoticeisapatternforreusingviews,similartoiOS.ReusingviewsarejustasimportantasoniOS,andthissubstantiallyhelpsperformance!Thisadapterisrathersimple,becauseitusesabuiltinsuperclass,ArrayAdapter,foradaptersworkingwitharraydata,butitillustrateshowtopopulateaListViewfromadataset.

AsyncTasks

InplaceofGrandCentralDispatchoniOS,onAndroidwehaveaccesstoAsyncTasks.AsyncTasksisadifferenttakeonexposingasynchronoustoolsinamorefriendlyway.AsyncTasksisabitoutofscopeforthisarticle,butIhighlyrecommendlookingoversomeofthedocumentation.

ActivityLifecycle

OneoftheprimarythingstowatchoutforcomingfromiOSdevelopmentistheAndroidlifecycle.LetsstartbylookingattheActivityLifecycleDocumentation:



Inessence,theactivitylifecycleisverysimilartotheUIViewControllerlifecycle.TheprimarydifferenceisthattheAndroidOScanberuthlesswithdestroyingactivities,anditisveryimportanttomakesurethatthedataandthestateoftheactivityaresaved,sothattheycanberestoredfromthesavedstateiftheyexistintheonCreate().ThebestwaytodothisisbyusingbundleddataandrestoringfromthesavedInstanceStateand/orIntents.Forexample,hereisthepartoftheTripListActivityfromoursampleprojectthatiskeepingtrackofthecurrentlyshownsubwayline:

publicstaticIntentgetTripListActivityIntent(Contextcontext,TripList.LineTypelineType){Intentintent=newIntent(context,TripListActivity.class);intent.putExtra(TripListActivityState.KEY_ACTIVITY_TRIP_LIST_LINE_TYPE,lineType.getLineName());returnintent;}

publicstaticfinalclassTripListActivityState{publicstaticfinalStringKEY_ACTIVITY_TRIP_LIST_LINE_TYPE="KEY_ACTIVITY_TRIP_LIST_LINE_TYPE";}

TripList.LineTypemLineType;

@OverrideprotectedvoidonCreate(BundlesavedInstanceState){super.onCreate(savedInstanceState);mLineType=TripList.LineType.getLineType(getIntent().getStringExtra(TripListActivityState.KEY_ACTIVITY_TRIP_LIST_LINE_TYPE));}

Anoteonrotation:thelifecyclecompletelyresetstheviewonrotation.Thatis,youractivitywillbedestroyedandrecreatedwhenarotationoccurs.Ifdataisproperlysavedinthesavedinstancestateandtheactivityrestoresthestatecorrectlyafteritscreation,thentherotationwillworkseamlessly.Manyappdevelopershaveissueswithappstabilitywhentheapprotates,becauseanactivitydoesnothandlestatechangesproperly.Beware!Donotlockyourappsrotationtosolvetheseissues,asthisonlyhidesthelifecyclebugsthatwillstilloccuratanotherpointintimewhentheactivityisdestroyedbytheOS.

FragmentLifecycle

TheFragmentLifecycleissimilartotheactivitylifecycle,withafewadditions.



Oneoftheproblemsthatcancatchdevelopersoffguardisregardingissuescommunicatingbetweenfragmentsandactivities.NotethattheonAttach()happensbeforeonActivityCreated().Thismeansthattheactivityisnotguaranteedtoexistbeforethefragmentiscreated.TheonActivityCreated()methodshouldbeusedwhenyousetinterfaces(delegates)totheparentactivity,ifneeded.

Fragmentsarealsocreatedanddestroyedaggressivelybytheneedsoftheoperatingsystem,andtokeeptheirstate,requirethesameamountofdiligenceasactivities.Hereisanexamplefromoursampleproject,wherethetriplistfragmentkeepstrackoftheTripListdata,aswellasthesubwaylinetype:

/***TheconfigurationflagsfortheTripListFragment.*/publicstaticfinalclassTripListFragmentState{publicstaticfinalStringKEY_FRAGMENT_TRIP_LIST_LINE_TYPE="KEY_FRAGMENT_TRIP_LIST_LINE_TYPE";publicstaticfinalStringKEY_FRAGMENT_TRIP_LIST_DATA="KEY_FRAGMENT_TRIP_LIST_DATA";}

/***Usethisfactorymethodtocreateanewinstanceof*thisfragmentusingtheprovidedparameters.**@paramlineTypethesubwaylinetoshowtripsfor.*@returnAnewinstanceoffragmentTripListFragment.*/publicstaticTripListFragmentnewInstance(TripList.LineTypelineType){TripListFragmentfragment=newTripListFragment();Bundleargs=newBundle();args.putString(TripListFragmentState.KEY_FRAGMENT_TRIP_LIST_LINE_TYPE,lineType.getLineName());fragment.setArguments(args);returnfragment;}

protectedTripListmTripList;protectedvoidsetTripList(TripListtripList){Bundlearguments=this.getArguments();arguments.putParcelable(TripListFragmentState.KEY_FRAGMENT_TRIP_LIST_DATA,tripList);mTripList=tripList;if(mTripArrayAdapter!=null){mTripArrayAdapter.clear();mTripArrayAdapter.addAll(mTripList.trips);}}

@OverridepublicvoidonCreate(BundlesavedInstanceState){super.onCreate(savedInstanceState);if(getArguments()!=null){mLineType=TripList.LineType.getLineType(getArguments().getString(TripListFragmentState.KEY_FRAGMENT_TRIP_LIST_LINE_TYPE));mTripList=getArguments().getParcelable(TripListFragmentState.KEY_FRAGMENT_TRIP_LIST_DATA);}}

NoticethatthefragmentalwaysrestoresitsstatefromthebundledargumentsinonCreate,andthatthecustomsetterfortheTripListmodelobjectaddstheobjecttothebundledargumentsaswell.Thisensuresthatifthefragmentisdestroyedandrecreated,suchaswhenthedeviceisrotated,thefragmentalwayshasthelatestdatatorestorefrom.

Layouts

SimilartootherpartsofAndroiddevelopment,thereareprosandconstospecifyinglayoutsinAndroidversusiOS.LayoutsarestoredashumanreadableXMLfilesintheres/layoutsfolder.

SubwayListViewLayout



HereisthesameviewoniOSwithaUITableViewandaUIButtonpinnedtothebottomviaAutoLayoutinInterfaceBuilder:



YoullnoticethattheAndroidlayoutfileismucheasiertoreadandunderstandwhatisgoingon.TherearemanypartstolayingoutviewsinAndroid,butwellcoverjustafewoftheimportantones.

TheprimarystructurethatyouwilldealwithwillbesubclassesofViewGroupRelativeLayout,LinearLayout,andFrameLayoutarethemostcommon.TheseViewGroupscontainotherviewsandexposepropertiestoarrangethemonscreen.

AgoodexampleistheuseofaRelativeLayoutabove.Arelativelayoutallowsustouseandroid:layout_alignParentBottom="true"inourlayoutabovetopinthebuttontothebottom.

Lastly,tolinklayoutstofragmentsoractivities,simplyusethatlayoutsresourceIDduringtheonCreateView:

@OverridepublicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,BundlesavedInstanceState){returninflater.inflate(R.layout.fragment_subway_listview,container,false);}

LayoutTips

Alwaysworkindp(densityindependentpixels)insteadofpixelsdirectly.Dontbothernudgingitemsforlayoutsinthevisualeditoroftenthevisualeditorwillputindividualpointsofspacingonobjectsinsteadofadjustingtheheightandwidthasyoumightlike.YourbestbetistoadjusttheXMLdirectly.Ifyoueverseethefill_parentvalueforalayoutheightorwidth,thisvaluewasdeprecatedyearsagoinAPI8andreplacedwithmatch_parent.

Seethetheresponsiveandroidapplicationsarticleformoretipsonthis.

Data

TheDataStorageOptionsavailableonAndroidarealsoverysimilartowhatisavailableoniOS:

SharedPreferencesNSUserDefaultsInmemoryobjectsSavingtoandfetchingfromfilestructureviatheinternalorexternalfilestoragesavingtothedocumentsdirectorySQLiteCoreData



TheprimarydifferenceisthelackofCoreData.Instead,AndroidoffersstraightaccesstotheSQLitedatabaseandreturnscursorobjectsforresults.HeadovertothearticleinthisissueaboutusingSQLiteonAndroidformoredetails.

AndroidHomework

Whatwevediscussedsofarbarelyscratchesthesurface.ToreallytakeadvantageofsomeofthethingsthatmakeAndroidspecial,Irecommendcheckingoutsomeofthesefeatures:

ActionBar,OverflowMenu,andtheMenuButtonCrossAppDataSharingRespondtocommonOSactionsTakeadvantageofJavasfeatures:generics,virtualmethodsandclasses,etc.GoogleCompatibilityLibrariesTheAndroidEmulator:installthex86HAXMplugintomaketheemulatorbutterysmooth.

FinalWordsMuchofwhatwasdiscussedinthisarticleisimplementedintheMBTAsubwaytransitsampleprojectonGitHub.Theprojectwasbuiltasawaytoillustratesimilarconceptssuchasapplicationstructure,handlingdata,andbuildingUIonthesameapplicationforbothplatforms.

WhilesomeofthepureimplementationdetailsareverydifferentonAndroid,itisveryeasytobringproblemsolvingskillsandpatternslearnedoniOStobear.Whoknows?MaybeunderstandinghowAndroidworksjustalittlebitbettermightprepareyouforthenextversionofiOS.

1. Source

2. SeeGooglesdocumentationforsupportingmultiplescreensizeshere.

3. Intentsdocumentation

4. SeeGooglesdocumentationformultipanetabletviewformoreinformation.

5. Thanks,NSHipster.

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