1
00:00:00,830 --> 00:00:04,800
Now that we've discussed some of
the challenges with mobile development and

2
00:00:04,800 --> 00:00:08,070
how Xamarin can help,
let's look at how it works.

3
00:00:09,250 --> 00:00:13,390
Each platform has its own feature set,
application framework, and

4
00:00:13,390 --> 00:00:14,630
execution differences.

5
00:00:16,290 --> 00:00:18,440
Xamarin has Base Class Libraries, or

6
00:00:18,440 --> 00:00:24,440
BCLs which provide many features
usually found in the .NET framework.

7
00:00:24,440 --> 00:00:28,210
They're implemented on the native
platform and exposed through the BCL.

8
00:00:29,270 --> 00:00:32,945
For example, in the BCL there's
support for Streams, IO,

9
00:00:32,945 --> 00:00:38,450
XML, Databases, and Networking.

10
00:00:38,450 --> 00:00:44,420
These provided base class libraries have
the same signature as the dot net BCL.

11
00:00:44,420 --> 00:00:47,860
So we can write the same code for
each platform.

12
00:00:47,860 --> 00:00:52,712
There are libraries provided by Xamarin
that are included in each platform project

13
00:00:52,712 --> 00:00:57,690
that provide implementation for
platform SDKs.

14
00:00:57,690 --> 00:01:00,660
All these features are plugged
into Visual Studio and

15
00:01:00,660 --> 00:01:05,010
include IntelliSense, tools and
compilation features.

16
00:01:06,100 --> 00:01:11,170
Xamarin provides bindings to the native
libraries and SDKs for each platform.

17
00:01:12,390 --> 00:01:16,770
Bindings are strongly typed and
are designed to follow C# standards.

18
00:01:18,540 --> 00:01:22,730
This gives developers a single
consistent programming syntax

19
00:01:22,730 --> 00:01:25,140
regardless of the target platform.

20
00:01:25,140 --> 00:01:29,910
For example, Java does not
have a concept of properties.

21
00:01:29,910 --> 00:01:34,150
So you use Get and
Set methods to update a class variable.

22
00:01:34,150 --> 00:01:38,700
But, Xamarin wraps them in
a property to match C# standards.

23
00:01:38,700 --> 00:01:39,670
Other than that,

24
00:01:39,670 --> 00:01:45,080
converting Java code to C# is relatively
simple cuz they share a lot of syntax.

25
00:01:46,260 --> 00:01:52,140
For Objective-C developers, there are many
differences between Objective-C and C#.

26
00:01:52,140 --> 00:01:54,540
So if you're converting from Objective-C,

27
00:01:54,540 --> 00:01:57,800
there's some articles in the teacher's
notes to help with the transition.

28
00:01:58,840 --> 00:02:02,690
Xamarin also allows us to
create an interop between

29
00:02:02,690 --> 00:02:05,540
any of our favorite Objective-C or
Java libraries.

30
00:02:06,570 --> 00:02:11,300
Using a declared syntax we can
bind any pre-existing library, and

31
00:02:11,300 --> 00:02:15,110
make it look like a C# class and
use it in our app.

32
00:02:16,360 --> 00:02:19,090
Compilation is where all
the magic happens, so

33
00:02:19,090 --> 00:02:21,330
we'll spend a few minutes
talking about how it works.

34
00:02:22,330 --> 00:02:26,570
As I said earlier, Android and iOS have
fundamental execution differences.

35
00:02:27,580 --> 00:02:30,705
Android uses a just in
time execution model or

36
00:02:30,705 --> 00:02:35,280
JIT which means that it compiles
to an intermediate language

37
00:02:35,280 --> 00:02:38,140
that is interpreted and
executed when the app launches.

38
00:02:40,120 --> 00:02:44,670
iOS on the other hand uses
an ahead-of-time execution model or

39
00:02:44,670 --> 00:02:49,340
AOT which means everything is compiled
directly to native assembly code and

40
00:02:49,340 --> 00:02:50,310
nothing is interpreted.

41
00:02:51,470 --> 00:02:57,080
All of this compilation happens through
special platform specific MS built targets

42
00:02:57,080 --> 00:03:01,020
that put all the pieces together and
produce the executable artifacts.

43
00:03:02,350 --> 00:03:06,340
It's important to know when compiling for
iOS you need a Mac.

44
00:03:06,340 --> 00:03:10,730
Because Apple's licensing does not
permit compiling on any other platform.

45
00:03:12,330 --> 00:03:15,030
Android requires your target SDKs and

46
00:03:15,030 --> 00:03:18,350
tools to be on your machine,
which can be downloaded when needed.