Cross Platform Mobile Development in C#

Ross Dargan

@rossdargan

What I’m going to cover

Target 95% of the UK mobile market in C#

With maximum code re-use

What I’m going to cover

What I won’t cover

The other cross platform options (http://propertycross.com/)

A full walkthrough of the tooling

Blackberry

Android56%

Windows12%

iOS27%

Blackberry4%

Other1%

UK Smartphone Landscape

Source: http://bit.ly/19d2thf

Native DevelopmentiOS

Objective C

Xcode

Windows Phone

C#/Visual Basic/F#

Visual Studio

Android

Java

Eclipse

IntelliJ

Xamarin

• C# and .NET for Android, iOS and Mac• Full native APIs

The bad…

• Price $2000 per dev per year• Still need a mac• Write once, run (and test!) everywhere• Tooling is still a bit immature (but the

support is great!)• Need to write each UI separately

UI Considerations

DEMOHello World

So… Sharing

SHARING CODEFile Linking

File Linking

DEMOFile Linking

File Linking

Pros

• Quick

Cons

• Messy code• Progressively more

difficult to maintain as you add implementations

• Very hard to test• File linking is a PITA to

remember as you add files

SHARING CODEPortable Class Libraries

Adding a PCL

Great… but

Still need platform specific code somehow…

SHARING CODEAbstract Classes

Multiple Concrete Classes

DEMOAbstract Classes

Abstract Classes

Pros

• Quick• Easier to maintain• Follows Open/Closed

principal

Cons

• Difficult to test• Pretty inflexible

SHARING CODEDependency Injection

Dependency Injection

• Helps separate code (Single responsibility)• Allows you to unit test’s discrete parts of

the implementation – no God classes• You can inject in platform specific

implementations• Inversion of Control allows you to swap

implementations easily

DEMOPCL & DI demo

Dependency Injection

Pros

• Very loosely coupled code (reuse)

• Unit tests are easy• Single Responsibility• Open/Closed

Cons

• • •

What are the downsides to using Dependency Injection?

It can be dangerous for your career because it may increase your overall knowledge of good API design. Once you learn how proper loosely coupled code can look like, it may turn out that you will have to decline lots of job offers because you would otherwise have to work with tightly coupled legacy apps. Happens to me a lot :)

Source: http://bit.ly/com6aD

Dependency Injection

Pros

• Very loosely coupled code (reuse)

• Unit tests are easy• Single Responsibility• Open/Closed

Cons

• More code• Bloated constructors

Can we squeeze any more reuse out?

MAXIMIZE UI CODE REUSEMVVM

MVVM

Platform Specific Code

Shared Code

Demo

Improving Code Reuse in 3 easy ways

• Heavy use of dependency injection– Allows different implementations for different

platforms

• Use PCLs (and file linking for the time being)

• Use View Models to reuse presentation code

3 layers of win

MVVMCross

Xamarin

Visual Studio

Links

• http://xamarin.com/• http://mvvmcross.wordpress.com/• http://propertycross.com/• https://github.com/rossdargan/Talks• Dependency Injection in .Net by Mark

Seemann (ISBN: 1-935182-50-1)• http://www.icndb.com/api/

Questions