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Cross-Platform Mobile Development In C#By Dan Hermes
Boston Mobile C# Developers' Group
Going NativeiOSAndroidWindows
The BasicsUIEvent life CyclesMulti-ThreadingWeb ServicesPatterns
UI – AndroidXamarin Studio
◦Xamarin Starter or Indie LicenseVisual Studio
◦2010+◦Professional+ (for plug-ins)◦Xamarin Business or Enterprise
License.axml
DEMO
UI - iOSXcodeYou need a Mac
◦Mac Mini◦macincloud.com
DEMO
Xcode
Android: Activities
An Activity is like a…◦Windows Process◦ASP.NET Page Life Cycle◦MVC Page Life Cycle
Back vs. Home
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Back• User is done with the Activity. Destroy it.
Home (or App Switcher)• Suspend the Activity. Place in the
background.
Activity States
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Activity Methods
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OnCreate – WHEN?Creating viewsInitializing variablesBinding static data to lists
Bundle – for Activity StateKey/value dictionaryBundle not null in OnCreate?
Restarting.
Activity Methods OnStart - before an activity becomes visible
◦ refresh current values of views
OnResume - start interacting with the user◦ Ramping up frame rates◦ Starting animations◦ Listening for GPS updates◦ Display any relevant alerts or dialogs◦ Wire up external event handlers◦ Undo operations in OnPause
OnPause◦ Commit changes to persistent data◦ Destroy or clean up other objects consuming resources◦ Ramp down frame rates and pausing animations◦ Unregister external event handlers or notification handlers◦ Clear dialogs and alerts
Activity Methods
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Activity MethodsOnStop - activity is no longer visible to
the user◦A new activity is being started and is
covering up this activity.◦An existing activity is being brought to
the foreground.◦The activity is being destroyed.
OnDestroy - final method◦ Kill threads
OnRestart – prior to a restart◦ Then OnStart – most reinit logic goes there
Managing StateBundle
◦Primitive data typesCustom Class
◦Complex data (ex. Bitmap)Roll Your Own
◦Circumvent the configuration change lifecycle
iOS App Life Cycle
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iOS Lifecycle Methods
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iOS Lifecycle Methods OnActivated
◦ upon launch or when app returns to foreground OnResignActivation
◦ upon an interruption such as a text or phone call DidEnterBackground
◦ user accepts the phone call ◦ save user data and tasks◦ remove sensitive information from the screen
WillEnterForeground
◦ App returns to foreground from background or suspension
◦ Restore state saved during DidEnterBackground◦ Then call OnActivated
WillTerminate
◦ App shuts down and process is destroyed◦ If multitasking is not available on the device or the OS
version◦ Memory is low◦ User manually terminates a backgrounded application.
iOS vs. AndroidApp Life Cycle
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iOS:Events, Protocols, and DelegatesEvents
◦Xamarin.iOS exposes .NET events on UIKit controls
Protocols ◦ Like a C# interface with optional methods◦ Xamarin.iOS implements using abstract
classesDelegates
◦ strongly and weakly typed◦ not be confused with C# delegates
Performance
Mobile users expect itDelays are annoying and alienate
usersAndroid Activities and iOS
Delegates?◦run in the foreground UI Thread
Long-running code should go into a…
Background Thread
Good Candidates for a Background ThreadOperations that
◦Make requests off of the device Retrieve data (web service, RSS feed) Connect to network Downloads
◦Run more than 50 milliseconds◦May block the user interface thread
Watchdog thread to kill the app
Async/Awaitasync
◦method declaration ◦lambda◦anonymous method
await◦code stops and waits◦spawns background thread◦UI thread is not blocked◦resumes at the same point in the
code
Async/Await
Async/AwaitGetStringAsync PutAsync PostAsync DeleteAsync
Async SupportXamarin.iOS
◦174 methodsXamarin.Android
◦337 methodsXamarin.MobileXamarin Component Store
Web ServicesRESTWCFSOAP
REST HttpWebRequest / WebClient RestSharp Hammock NSURLConnection ServiceStack
Web PatternsAsync/AwaitMVCMVVMCross
MVCModel
◦Can use themViews
◦Must use themControllers
◦Android Activities◦iOS AppDelegates
Cross-Platform Mobile Development In C#Dan HermesMobile Consultant
Lexicon Systems
Website: www.lexiconsystemsinc.comEmail: [email protected]: 781-526-0738Twitter: @lexiconsystemsBlog: www.itshopkeeping.com
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