Cross platform mobile development in c#

Cross-Platform Mobile Development In C#By Dan Hermes

dan@lexiconsystemsinc.comwww.lexiconsystemsinc.com

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

Image courtesy of Xamarin

Back• User is done with the Activity. Destroy it.

Home (or App Switcher)• Suspend the Activity. Place in the

background.

Activity States

Image courtesy of Xamarin

Activity Methods

Image courtesy of Xamarin

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

Image courtesy of Xamarin

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

Image courtesy of Xamarin

iOS Lifecycle Methods

Image courtesy of Xamarin

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

Image courtesy of Xamarin

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: dan@lexiconsystemsinc.comPhone: 781-526-0738Twitter: @lexiconsystemsBlog: www.itshopkeeping.com

Are You Mobilizing?