Do you have a great knowledge about C#? Maybe you’ve already built a great mobile app on Windows Phone or Windows 8 or even Windows 10? Would you like to be able to use your knowledge to build an Android app without having to resort to other languages or IDEs? This is possible using Xamarin! In this session, Gill Cleeren will take you through the creation of your first Android application: Joe’s Coffee Store. Along the way, you will learn the basic concepts of Android such as Activities and see how we can use these from Xamarin.Android. We’ll need to connect with services to get access to data and we’ll learn how to navigate in the app. You’ll see we can do this all of this directly from Visual Studio. We will finish the session by looking at how we can deploy the application to the Google Play Store so it’s ready for our users! You’ll walk away wanting to port your code to Android!

1. Building your first Android app
using Xamarin
Gill Cleeren
@gillcleeren

2. Hi, I’m Gill!
Gill Cleeren
MVP and Regional Director
.NET Practice Manager @ Ordina
Trainer & speaker
@gillcleeren
gill@snowball.be

3. I’m a Pluralsight author!
• Courses on Xamarin, WPF, social and HTML5
• http://gicl.me/mypscourses

4. Agenda
• Overview of Xamarin and Xamarin.Android
• Xamarin.Android fundamentals
• Creating a detail screen
• Lists and navigation
• Navigating from master to detail
• Optimizing the application
• Preparing for store deployment

5. Targets of this talk
• Understanding the fundamentals of Android app development with
Xamarin
• See how a fully working app can be built

6. The demo scenario
• Android Coffee Store Manager
• List of coffees
• Navigation to details page

7. DEMO
Looking at the finished application

8. Overview of Xamarin and
Xamarin.Android

9. Hello Xamarin
• Xamarin enables developers to reach all major mobile platforms!
• Native User Interface
• Native Performance
• Shared Code Across Platforms
• C# & .NET Framework
• Toolset on top of Visual Studio
• Enables VS to create native iOS and Android apps
• Commercial product

10. Write Everything in C#
iOS, Android, Windows, Windows Phone, Mac
Billions of Devices covered!

11. The Xamarin platform
Xamarin
Xamarin.Android Xamarin.iOS Xamarin Forms

12. Xamarin.Android exposes many extra device
types

13. Xamarin.Android
Anything you can do in Java/Android can be done in C# and
Visual Studio (or Xamarin Studio) with Xamarin!

14. How Xamarin works on Android
• Mono VM + Java VM execute side-by-side (supports both Dalvik and
ART)
• Mono VM JITs IL into native code and executes most of your code
• Can utilize native libraries directly as well as .NET BCL

15. A word on code-sharing
• Xamarin brings development time through the use of code-sharing
• Possible (currently!) using
• Shared projects:
• allows organizing the shared code
• #if directives for platform specific code
• PCL
• “include” the platforms we want to support
• Abstract to interfaces where platforms have specific implementations

16. Target architecture for a Xamarin app

17. Preparing for
Android development

18. What you need for Xamarin.Android
development
• Xamarin license (Xamarin.Android)
• PC or Mac
• Visual Studio or Xamarin Studio
• Android SDK and Emulators (installed via Xamarin setup)
• Emulator
• Device (not really required but...)

19. Installing Xamarin.Android

20. A word on emulators
• Setup will install some basic emulators for you
• They’re great… for drinking a lot of coffee

21. Alternatives for the default emulators
• Possible options
• Genymotion
-Requires VirtualBox under the hood
• HAXM drivers
• Android Player from Xamarin
• Microsoft Android emulator
• Hyper-V
• Preferred option on Windows

22. DEMO
A quick look at the development setup

23. Xamarin.Android
fundamentals

24. File  New Project

25. File  New Project

26. Fundamental #1: Activities
• Apps are collections of activities
• A view == an activity (for now )
• Apps don’t have an “entry point”
• No single code line which is called by the OS
• Apps start when Android creates one of the classes of the app
• App then gets loaded into memory

27. Fundamental #1: Activities
• When opening an application, the OS creates the first Activity
• Activity is a specific class
• Defines UI and behaviour for a single task
• Corresponds to a single app screen
• App gets loaded in memory
OS
User launches app
Activity
Android loads app
In memory

28. Fundamental #1: Activities
• One activity needs to be the “entry point” for the app:
MainLauncher=True

29. Activity lifecycle

30. Activity lifecycle
• We can of course override these methods
• OnCreate:
• Create views, initialize variables, and do other prep work before the user sees the
Activity
• This method is called only once when the Activity is loaded into memory
• OnResume
• Perform any tasks that need to happen every time the Activity returns to the device
screen
• OnPause
• Perform any tasks that need to happen every time the Activity leaves the device screen

31. Activity lifecycle in effect

32. Fundamental #2: Views
• The layout of the app is contained in *.axml files
• AXML: Android designer file / Android XML
• First view of the app is named Main.axml
• Can be any name really
• AXML files live in the Resources/layout folder

33. The designer for Xamarin.Android views

34. The designer for Xamarin.Android views

35. View code

36. Connecting and accessing controls from code
• Linking a view with an activity is done using SetContentView

37. Connecting and accessing controls from code
• We can name controls using the ID property
• The Android designer maps the control to the Resource class and assigns it a
resource ID
• The code representation of a control is
linked to the visual representation
of the control in the
designer via the Id
property

38. Connecting and accessing controls from code
• Once we have created the controls, we can access them from code
• Field name is used for lookup

39. Fundamental #3: Application manifest
• An Android app contains a manifest file
• Contains a list of all resources, properties… that make up the application
• Also contains name, list of permissions… that the application has received
Images
Icons
*.axml
Others
Android Manifest file

41. DEMO
Creating our first Android application together!

42. Navigation and lists

43. Fundamental #4: ListViews and adapters
• Used very commonly in Android
• Common way to present lists of rows
• Each row is represented using a standard style or customized
• Consists out of
• ListView: visual part
• Adapter: feeds data to ListView

44. Fundamental #4: ListViews and adapters

45. Important classes
• ListView
• ListActivity
• BaseAdapter
• ArrayAdapter & ArrayAdapter<T>

46. ListActivity and the built-in ArrayAdapter<T>
[Activity(Label = "Coffees", MainLauncher = true, Icon = "@drawable/icon")]
public class CoffeeScreenActivity: ListActivity
{
string[] coffees;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
coffees= new string[] { "Coffee 1","Coffee 2", "Coffee 3"};
ListAdapter = new ArrayAdapter<String>(
this,
Android.Resource.Layout.SimpleListItem1,
coffees);
}
}

47. Implementing your own adapter
• In most cases, the ArrayAdapter won’t be enough
• We’ll need to create our own adapter
• Inherits from BaseAdapter
• Things we need to implement
• Count:
• To tell the control how many rows are in the data
• GetView:
• To return a View for each row, populated with data. This method has a parameter for the
ListView to pass in an existing, unused row for re-use
• GetItemId:
• Return a row identifier (typically the row number, although it can be any long value that you
like)
• this[int] indexer:
• To return the data associated with a particular row number

48. Handling row clicks
• To handle row clicks, we need to implement OnListItemClick
protected override void OnListItemClick(ListView l, View v, int position, long id)
{
var t = items[position];
//do something
}

49. DEMO
Adding a ListView and an adapter

50. Customizing the ListView with other row views

51. Customizing the ListView with other row views

52. Customizing the ListView with other row views

53. DEMO
Using the built-in row views

54. Creating your own row views
• Custom row layouts are AXML files in Resources/layout
• Are loaded by Id using a custom adapter
• View can contain any number of display classes with custom colors, fonts…

55. Creating your own
row view
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:padding="8dp"
android:orientation="horizontal">
<ImageView
android:id="@+id/CoffeeImageView"
android:layout_width="50dp"
android:layout_height="50dp"
android:padding="5dp" />
<LinearLayout
android:id="@+id/TextFields"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dip">
<TextView
android:id="@+id/CoffeeNameText"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/PriceText"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>

56. Using your custom row view
public override View GetView(int position, View convertView, ViewGroup parent)
{
//custom view
var item = items[position];
if (convertView == null)
{
convertView = context.LayoutInflater.Inflate (Resource.Layout.CoffeeRowView, null);
}
convertView.FindViewById<ImageView>
(Resource.Id.CoffeeImageView).SetImageResource(
imageRepository.ImageNameToResourceInt(item.ImageId.ToString()));
convertView.FindViewById<TextView>
(Resource.Id.CoffeeNameText).Text = item.CoffeeName;
convertView.FindViewById<TextView>
(Resource.Id.PriceText).Text = item.Price.ToString();
return convertView;
}

57. DEMO
Adding our own custom row view

58. Fundamental #5: Intents
• An Intent is an abstract concept for some sort of operation that
should be performed in Android
• Navigating to another activity
• Often, launching an external application (= built-in) with the intent of doing
something
• Make a phone call
• Launch a URI
• Map an address
• An intent often consist out of
• What the intent is
• The data needed for the intent
• Phone number to call

59. Intent of making a phone call
• ActionCall asks Android for an Activity to make a phone call

60. Intent of navigating to another screen
• StartActivity can be used to start another activity
• PutExtra() is used to pass data from one activity to the other
var intent = new Intent ();
intent.SetClass (this, typeof(CoffeeDetailActivity));
intent.PutExtra ("selectedCoffeeId", t.CoffeeId);
StartActivity (intent);

61. Receiving information from the intent
protected override void OnCreate (Bundle bundle)
{
base.OnCreate (bundle);
SetContentView (Resource.Layout.Main);
var selectedCoffeeId = Intent.Extras.GetInt ("selectedCoffeeId", 0);
Coffee coffee = DataService.GetCoffeeById (selectedCoffeeId);
}

62. DEMO
Navigating from the List
to the Detail page

63. Optimizing
the application

64. Managing strings in strings.xml
• We can have Android store string values for us
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">Hello World, Click Me!</string>
<string name="app_name">AndroidCoffeeStore</string>
<string name="coffeeNameLabel">Coffee name</string>
</resources>
<TextView
android:text="@string/coffeeNameLabel"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/CoffeeNameLabel" />

65. Making the app multi-language

66. Application drawables
• We can add drawables: application icons
• Adding all resolutions makes sure the icons look good on all screens
• Filenames are the same
• Folder name identifies the resolution

67. Application drawables
• We can select an image in the project properties
• This now becomes the icon for the application within Android

68. DEMO
Adding resources
and drawables to the application

69. Deploying
to the store

70. Publishing your work
• Marketplace is most common option
• Often, more than one is used (Google Play, Amazon, GetJar…)
• Email or website is often for a more closed distribution
• Also require less work to prepare the application for distribution
• Google Play is best known store
• Allows users to discover, download, rate, and pay for applications by clicking a
single icon either on their device or on their computer
• Google Play also provides tools to assist in the analysis of sales and market
trends and to control which devices and users may download an application

71. Summary
• Xamarin.Android leverages your C# knowledge to build apps for
Android
• Concepts of Android mean a learning curve

72. Thanks!

73. Q&A

74. VISUG Partners

75. Building your first Android app
using Xamarin
Gill Cleeren
@gillcleeren