Inter-App Communication

Appscommunicateonlyindirectlywithotherappsonadevice.YoucanuseAirDroptosharefilesanddatawithotherapps.YoucanalsodefineacustomURLschemesothatappscansendinformationtoyourappusingURLs.

Note:Youcanalsosendfilesbetweenappsusinga

UIDocumentInteractionController

object
oradocumentpicker.Forinformationaboutaddingsupportforadocumentinteractioncontroller,seeDocument
InteractionProgrammingTopicsforiOS.Forinformationaboutusingadocumentpickertoopenfiles,seeDocument
PickerProgrammingGuide.

SupportingAirDrop

AirDropletsyousharephotos,documents,URLs,andothertypesofdatawithnearbydevices.AirDroptakesadvantageofpeer-to-peernetworkingtofindnearbydevicesandconnecttothem.

SendingFilesandDatatoAnotherApp

TosendfilesanddatausingAirDrop,usea

UIActivityViewController

object
todisplayanactivitysheetfromyouruserinterfaceusing.Whencreatingthisviewcontroller,youspecifythedataobjectsthatyouwanttoshare.Theviewcontrollerdisplaysonlythoseactivitiesthatsupportthespecifieddata.ForAirDrop,youcanspecify
images,strings,URLs,andseveralothertypesofdata.Youcanalsopasscustomobjectsthatadoptthe

UIActivityItemSource

protocol.
Todisplayanactivityviewcontroller,youcanusecodesimilartothatshowninListing6-1.Theactivity
viewcontrollerautomaticallyusesthetypeofthespecifiedobjecttodeterminewhatactivitiestodisplayintheactivitysheet.YoudonothavetospecifytheAirDropactivityexplicitly.However,youcanpreventthesheetfromdisplayingspecifictypes
usingtheviewcontroller’s

excludedActivityTypes

property.
WhendisplayinganactivityviewcontrolleroniPad,youmustuseapopover.

Listing6-1DisplayinganactivitysheetoniPhone

-(void)displayActivityControllerWithDataObject:(id)obj{

UIActivityViewController*vc=[[UIActivityViewControlleralloc]

initWithActivityItems:@[obj]applicationActivities:nil];

[selfpresentViewController:vcanimated:YEScompletion:nil];

}

Formoreinformationaboutusingtheactivityviewcontroller,seeUIActivityViewController
ClassReference.Foracompletelistofactivitiesandthedatatypestheysupport,seeUIActivity
ClassReference.

ReceivingFilesandDataSenttoYourApp

ToreceivefilessenttoyourappusingAirDrop,dothefollowing:

InXcode,declaresupportforthedocumenttypesyourappiscapableofopening.

Inyourappdelegate,implementthe

application:openURL:sourceApplication:annotation:

method.
Usethatmethodtoreceivethedatathatwassentbytheotherapp.

Bepreparedtolookforfilesinyourapp’s

Documents/Inbox

directoryand
movethemoutofthatdirectoryasneeded.

TheInfotabofyourXcodeprojectcontainsaDocumentTypessectionforspecifyingthedocumenttypesyourappsupports.Ataminimum,youmustspecifyanameforyourdocumenttypeandoneormoreUTIsthat
representthedatatype.Forexample,todeclaresupportforPNGfiles,youwouldinclude

public.png

astheUTIstring.iOSusesthespecified
UTIstodetermineifyourappiseligibletoopenagivendocument.
Aftertransferringaneligibledocumenttoyourapp’scontainer,iOSlaunchesyourapp(ifneeded)andcallsthe

application:openURL:sourceApplication:annotation:

method
ofitsappdelegate.Ifyourappisintheforeground,youshouldusethismethodtoopenthefileanddisplayittotheuser.Ifyourappisinthebackground,youmightdecideonlytonotethatthefileistheresothatyoucanopenitlater.Becausefiles
transferredviaAirDropareencryptedusingdataprotection,youcannotopenfilesunlessthedeviceiscurrentlyunlocked.
FilestransferredtoyourappusingAirDropareplacedinyourapp’s

Documents/Inbox

directory.
Yourapphaspermissiontoreadanddeletefilesinthisdirectorybutitdoesnothavepermissiontowritetofiles.Ifyouplantomodifythefile,youmustmoveitoutofthe

Inbox

directory
beforedoingso.Itisrecommendedthatyoudeletefilesfromthe

Inbox

directorywhenyounolongerneedthem.
Formoreinformationaboutsupportingdocumenttypesinyourapp,seeDocument-Based
AppProgrammingGuideforiOS.

UsingURLSchemestoCommunicatewithApps

AURLschemeletsyoucommunicatewithotherappsthroughaprotocolthatyoudefine.Tocommunicatewithanappthatimplementssuchascheme,youmustcreateanappropriatelyformattedURLandaskthesystem
toopenit.Toimplementsupportforacustomscheme,youmustdeclaresupportfortheschemeandhandleincomingURLsthatusethescheme.

Note:Appleprovidesbuilt-insupportforthe

http

,

mailto

,

tel

,
and

sms

URLschemesamongothers.Italsosupports

http

–based
URLstargetedattheMaps,YouTube,andiPodapps.Thehandlersfortheseschemesarefixedandcannotbechanged.IfyourURLtypeincludesaschemethatisidenticaltoonedefinedbyApple,theApple-providedappislaunchedinsteadofyourapp.Forinformation
abouttheschemessupportedbyapple,seeApple
URLSchemeReference.

SendingaURLtoAnotherApp

WhenyouwanttosenddatatoanappthatimplementsacustomURLscheme,createanappropriatelyformattedURLandcallthe

openURL:

method
oftheappobject.The

openURL:

methodlaunchestheappwiththeregisteredschemeandpassesyourURLtoit.Atthatpoint,controlpassesto
thenewapp.
Thefollowingcodefragmentillustrateshowoneappcanrequesttheservicesofanotherapp(“todolist”inthisexampleisahypotheticalcustomschemeregisteredbyanapp):

NSURL*myURL=[NSURLURLWithString:@"todolist://www.acme.com?Quarterly%20Report#200806231300"];

[[UIApplicationsharedApplication]openURL:myURL];

IfyourappdefinesacustomURLscheme,itshouldimplementahandlerforthatschemeasdescribedinImplementing
CustomURLSchemes.Formoreinformationaboutthesystem-supportedURLschemes,includinginformationabouthowtoformattheURLs,seeApple
URLSchemeReference.

ImplementingCustomURLSchemes

IfyourappcanreceivespeciallyformattedURLs,youshouldregisterthecorrespondingURLschemeswiththesystem.AppsoftenusecustomURLschemestovendservicestootherapps.Forexample,theMapsapp
supportsURLsfordisplayingspecificmaplocations.

RegisteringCustomURLSchemes

ToregisteraURLtypeforyourapp,includethe

CFBundleURLTypes

keyinyourapp’s

Info.plist

file.
The

CFBundleURLTypes

keycontainsanarrayofdictionaries,eachofwhichdefinesaURLschemetheappsupports.Table
6-1describesthekeysandvaluestoincludeineachdictionary.

Table6-1Keysandvaluesofthe

CFBundleURLTypes

property

Key	Value
CFBundleURLName	AstringcontainingtheabstractnameoftheURLscheme.Toensureuniqueness,itisrecommendedthatyouspecifyareverse-DNSstyleofidentifier,forexample, com.acme.myscheme . Thestringyouspecifyisalsousedasakeyinyourapp’s InfoPlist.strings file.Thevalueofthekeyisthehuman-readableschemename.
CFBundleURLSchemes	AnarrayofstringscontainingtheURLschemenames—forexample, http , mailto , tel , and sms .

Note:Ifmorethanonethird-partyappregisterstohandlethesameURLscheme,thereiscurrentlynoprocessfordeterminingwhichappwillbegiventhatscheme.

HandlingURLRequests

AnappthathasitsowncustomURLschememustbeabletohandleURLspassedtoit.AllURLsarepassedtoyourapp
delegate,eitheratlaunchtimeorwhileyourappisrunningorinthebackground.TohandleincomingURLs,yourdelegateshouldimplementthefollowingmethods:

Usethe

application:willFinishLaunchingWithOptions:

and

application:didFinishLaunchingWithOptions:

methods
toretrieveinformationabouttheURLanddecidewhetheryouwanttoopenit.Ifeithermethodreturns

NO

,
yourapp’sURLhandlingcodeisnotcalled.

Usethe

application:openURL:sourceApplication:annotation:

method
toopenthefile.

IfyourappisnotrunningwhenaURLrequestarrives,itislaunchedandmovedtotheforegroundsothatitcanopentheURL.Theimplementationofyour

application:willFinishLaunchingWithOptions:

or

application:didFinishLaunchingWithOptions:

method
shouldretrievetheURLfromitsoptionsdictionaryanddeterminewhethertheappcanopenit.Ifitcan,return

YES

and
letyour

application:openURL:sourceApplication:annotation:

(or

application:handleOpenURL:

)
methodhandletheactualopeningoftheURL.(Ifyouimplementbothmethods,bothmustreturn

YES

before
theURLcanbeopened.)Figure6-1showsthemodifiedlaunchsequenceforanappthatisaskedtoopenaURL.
Figure6-1LaunchinganapptoopenaURL


IfyourappisrunningbutisinthebackgroundorsuspendedwhenaURLrequestarrives,itismovedtotheforegroundtoopentheURL.Shortlythereafter,thesystemcallsthedelegate’s

application:openURL:sourceApplication:annotation:

to
checktheURLandopenit.Figure6-2showsthemodifiedprocessformovinganapptotheforegroundtoopenaURL.
Figure6-2Wakingabackgroundapptoopen
aURL


Note:AppsthatsupportcustomURLschemescanspecifydifferentlaunchimagestobedisplayedwhenlaunchingtheapptohandleaURL.Formoreinformationabouthowtospecify
theselaunchimages,seeDisplaying
aCustomLaunchImageWhenaURLisOpened.

AllURLsarepassedtoyourappinan

NSURL

object.
ItisuptoyoutodefinetheformatoftheURL,butthe

NSURL

classconformstotheRFC1808specificationandthereforesupportsmostURLformatting
conventions.Specifically,theclassincludesmethodsthatreturnthevariouspartsofaURLasdefinedbyRFC1808,includingtheuser,password,query,fragment,andparameterstrings.The“protocol”foryourcustomschemecanusetheseURLpartsforconveying
variouskindsofinformation.
Intheimplementationof

application:openURL:sourceApplication:annotation:

shown
inListing6-2,thepassed-inURLobjectconveysapp-specificinformationinitsqueryandfragmentparts.Thedelegateextractsthisinformation—inthis
case,thenameofato-dotaskandthedatethetaskisdue—andwithitcreatesamodelobjectoftheapp.ThisexampleassumesthattheuserisusingaGregoriancalendar.Ifyourappsupportsnon-Gregoriancalendars,youneedtodesignyourURLschemeaccordingly
andbepreparedtohandlethoseothercalendartypesinyourcode.

Listing6-2HandlingaURLrequestbasedonacustomscheme

-(BOOL)application:(UIApplication*)applicationopenURL:(NSURL*)url

sourceApplication:(NSString*)sourceApplicationannotation:(id)annotation{

if([[urlscheme]isEqualToString:@"todolist"]){

ToDoItem*item=[[ToDoItemalloc]init];

NSString*taskName=[urlquery];

if(!taskName||![selfisValidTaskString:taskName]){//musthaveataskname

returnNO;

}

taskName=[taskNamestringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

item.toDoTask=taskName;

NSString*dateString=[urlfragment];

if(!dateString||[dateStringisEqualToString:@"today"]){

item.dateDue=[NSDatedate];

}else{

if(![selfisValidDateString:dateString]){

returnNO;

}

//format:yyyymmddhhmm(24-hourclock)

NSString*curStr=[dateStringsubstringWithRange:NSMakeRange(0,4)];

NSIntegeryeardigit=[curStrintegerValue];

curStr=[dateStringsubstringWithRange:NSMakeRange(4,2)];

NSIntegermonthdigit=[curStrintegerValue];

curStr=[dateStringsubstringWithRange:NSMakeRange(6,2)];

NSIntegerdaydigit=[curStrintegerValue];

curStr=[dateStringsubstringWithRange:NSMakeRange(8,2)];

NSIntegerhourdigit=[curStrintegerValue];

curStr=[dateStringsubstringWithRange:NSMakeRange(10,2)];

NSIntegerminutedigit=[curStrintegerValue];

NSDateComponents*dateComps=[[NSDateComponentsalloc]init];

[dateCompssetYear:yeardigit];

[dateCompssetMonth:monthdigit];

[dateCompssetDay:daydigit];

[dateCompssetHour:hourdigit];

[dateCompssetMinute:minutedigit];

NSCalendar*calendar=[s[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];

NSDate*itemDate=[calendardateFromComponents:dateComps];

if(!itemDate){

returnNO;

}

item.dateDue=itemDate;

}

[(NSMutableArray*)self.listaddObject:item];

returnYES;

}

returnNO;

}

BesuretovalidatetheinputyougetfromURLspassedtoyourapp;seeValidating
InputandInterprocessCommunicationinSecure
CodingGuidetofindouthowtoavoidproblemsrelatedtoURLhandling.TolearnaboutURLschemesdefinedbyApple,seeApple
URLSchemeReference.

DisplayingaCustomLaunchImageWhenaURLisOpened

AppsthatsupportcustomURLschemescanprovideacustomlaunchimageforeachscheme.WhenthesystemlaunchesyourapptohandleaURLandnorelevantsnapshotisavailable,itdisplaysthelaunchimageyou
specify.Tospecifyalaunchimage,provideaPNGimagewhosenameusesthefollowingnamingconventions:
<basename>

-

<url_scheme><other_modifiers>

.png

Inthisnamingconvention,basenamerepresentsthebaseimagenamespecifiedbythe

UILaunchImageFile

key
inyourapp’s

Info.plist

file.Ifyoudonotspecifyacustombasename,usethestring

Default

.
The<url_scheme>portionofthenameisyourURLschemename.Tospecifyagenericlaunchimageforthe

myapp

URLscheme,youwouldinclude
animagefilewiththename

Default-myapp@2x.png

intheapp’sbundle.(The@2xmodifiersignifiesthattheimageisintendedforRetinadisplays.
Ifyourappalsosupportsstandardresolutiondisplays,youwouldalsoprovidea

Default-myapp.png

image.)
Forinformationabouttheothermodifiersyoucanincludeinlaunchimagenames,seethedescriptionofthe

UILaunchImageFile

name
keyinInformation
PropertyListKeyReference.