Now that we've discussed some of the challenges with mobile development and

how Xamarin can help, let's look at how it works.

Each platform has its own feature set, application framework, and

execution differences.

Xamarin has Base Class Libraries, or

BCLs which provide many features usually found in the .NET framework.

They're implemented on the native platform and exposed through the BCL.

For example, in the BCL there's support for Streams, IO,

XML, Databases, and Networking.

These provided base class libraries have the same signature as the dot net BCL.

So we can write the same code for each platform.

There are libraries provided by Xamarin that are included in each platform project

that provide implementation for platform SDKs.

All these features are plugged into Visual Studio and

include IntelliSense, tools and compilation features.

Xamarin provides bindings to the native libraries and SDKs for each platform.

Bindings are strongly typed and are designed to follow C# standards.

This gives developers a single consistent programming syntax

regardless of the target platform.

For example, Java does not have a concept of properties.

So you use Get and Set methods to update a class variable.

But, Xamarin wraps them in a property to match C# standards.

Other than that,

converting Java code to C# is relatively simple cuz they share a lot of syntax.

For Objective-C developers, there are many differences between Objective-C and C#.

So if you're converting from Objective-C,

there's some articles in the teacher's notes to help with the transition.

Xamarin also allows us to create an interop between

any of our favorite Objective-C or Java libraries.

Using a declared syntax we can bind any pre-existing library, and

make it look like a C# class and use it in our app.

Compilation is where all the magic happens, so

we'll spend a few minutes talking about how it works.

As I said earlier, Android and iOS have fundamental execution differences.

Android uses a just in time execution model or

JIT which means that it compiles to an intermediate language

that is interpreted and executed when the app launches.

iOS on the other hand uses an ahead-of-time execution model or

AOT which means everything is compiled directly to native assembly code and

nothing is interpreted.

All of this compilation happens through special platform specific MS built targets

that put all the pieces together and produce the executable artifacts.

It's important to know when compiling for iOS you need a Mac.

Because Apple's licensing does not permit compiling on any other platform.

Android requires your target SDKs and

tools to be on your machine, which can be downloaded when needed.