What's Xamarin.Android? This deck will allow you to get started fast at building C# apps with it :)

1. Creare app native su
iOS, Android, Mac &
Windows in C#
Introduzione a Xamarin.Android

2. Gli speaker di oggi
Guido Magrin
Xamarin & Microsoft Student Partner
Xamarin Certified Developer
@GuidoMagrin

3. Dove trovo le slide?
http://www.slideshare.net/guidomagrin

4. Gli Xamarin Student Partner
https://www.facebook.com/XSAMilano

5. Oggi parleremo di…
Xamarin.Android

6. Chi ha già
sentito parlare di
Xamarin.Android?

7. Xamarin + Xamarin.Forms
Approccio offerto da Xamarin.Forms:
Codice UI condiviso, controlli nativi
Approccio tradizionale di Xamarin
Shared UI Code

8. .NET Android APIs | 100% coverage

9. Qualsiasi cosa si possa fare in
Java può essere fatta in C#
con Xamarin in Visual Studio

10. Xamarin Studio
PC o Mac
Plugin Visual Studio
VS 2010 e superiore
Ambienti di Sviluppo

11. Integrazione in Visual Studio
Una soluzione sola per:
• iOS
• Android
• Windows Phone
• Windows Store
Tutti i plugin e le funzioni
di Visual Studio:
• ReSharper
• Team Foundation Server

12. Integrazione in Visual Studio
Debugging su:
• Emulatori
• Dispositivi
Integrati nella toolbar:
• Stato
• Logs
• Lista di dispositivi

13. Xamarin Studio
• Ottimizzato per lo sviluppo
cross-platform
• Accedi alle API native con
l’autocompletamento
• Designer per Android e iOS
• Debugging avanzato su
emulatore o dispositivo

14. Designer per Xamarin Android
• Il migliore designer per Android
• Disponibile per
• Xamarin Studio
• Visual Studio
• Crea facilmente l’interfaccia
utente tramite drag & drop
• Affronta facilmente il problema
del rescaling e della
frammentazione di Android.
• Layout salvati in file XML
Android standard

15. Cosa impareremo oggi?
• The package
• Activities
• Liste

16. The package

17. The package
The build process bundles the app into a single file with .apk
extension.
It’s the package that needs to be uploaded in the Google Store to
publish the app.

18. Permissions
The manifest file controls which
features of the platform the app can
use.

19. Images and screen density
• Android runs on many devices with
different screens and resolutions
• You supply the images in different sizes
with the same name
• You distinguish them applying a naming
convention to the folder where the image
is stored

20. Images and screen density
• Every application should have an icon and a
label
• It’s set in the manifest file

21. Icons and label
• Also activities can have their own icon and
label
• They are displayed in the navigation bar
• They are defined in the Activity attribute
[Activity(Label = "AndroidFundamentals", MainLauncher = true,
Icon = "@drawable/icon")]
public class MainActivity : Activity
{
...
}

22. API levels
• Every Android version is identified by:
– Version number (4.4, 5.1, etc.)
– Nickname (Kit Kat, Lollipop, etc.)
– API Level (19, 22, etc.)
• Every device supports a specific API level
• It’s helpful to understand if an app can run on a specific
device

23. API levels
• In the properties of the project you can define:
– Target API: the API level used to build the package
– Minimum API: the minimum set of supported API level
– Target Android version: API level that the app expects to use
• If API Level < Minimum API the app won’t be installed

24. API Level Check
• If API Level < Target API some APIs mightn’t be available
• You can detect, in code, the current API Level:
if (Android.OS.Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.Lollipop)
{
//use APIs that are available in Lollipop
}
else
{
//fallback to old APIs
}

25. Resources
• Resources can be managed using naming conventions
applied to the folder
• Examples:
– resources/drawable-it: it contains the images used on an Italian
device
– layout-land: it contains the layouts to use in landscape mode
• The Build Action must be set to AndroidResource

26. Resources
• Layout: interfaces
• Drawable: images
• Values: generic strings (localization)
• Color: XML files that define colors

27. Package
DEMO

28. La prima app
Xamarin.Forms

29. Domanda 1
Un’applicazione Android funziona senza vincoli particolari su qualsiasi
telefono sul quale sia installato Android:
a) Vero
b) Falso

30. Domanda 1
Un’applicazione Android funziona senza vincoli particolari su qualsiasi
telefono sul quale sia installato Android:
a) Vero
b) Falso

31. Domanda 2
Come si chiama il file tramite il quale posso modificare le impostazioni
di un package Android?
a) Paper
b) Resources
c) Manifest
d) Document

32. Domanda 2
Come si chiama il file tramite il quale posso modificare le impostazioni
di un package Android?
a) Paper
b) Resources
c) Manifest
d) Document

33. Domanda 3
Quali sono i tipi di Resources disponibili in un’app Android?
a) Layout, Images, Values, Brushes
b) Layout, Drawables, Values, Color
c) Disposition, Drawables, Enumerables, Color
d) UIDefine, Images, Enumerables, Brushes

34. Domanda 3
Quali sono i tipi di Resources disponibili in un’app Android?
a) Layout, Images, Values, Brushes
b) Layout, Drawables, Values, Color
c) Disposition, Drawables, Enumerables, Color
d) UIDefine, Images, Enumerables, Brushes

35. Activities

36. Activities
• An activity is a page that shows some content to the user.
• An application is usually composed by multiple activities.

37. Activities
• In Xamarin, an Activity is composed by:
– A XML file, that describes the layout (optional, it can be done also by
code)
– A code behind class, that manages the interactions with the UI
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout ...>
<TextView ... />
<EditText ... />
<Button ... />
</LinearLayout>
public class MainActivity : Activity
{
...
}
UI defined with XML C# class that inherits
from Activity and it’s
decorated with the

38. The Main Activity
It’s the activity that is automatically launched when the user
starts an app
The MainLauncher property
of the Activity attribute is
used to define the main activity
[Activity(MainLauncher = true]
public class MainActivity : Activity
{
...
}

39. Access to controls
To gain access to a control in code you need to assign an ID
Assign an ID in the XML <TextView android:id="@+id/PhoneNumber" />
// aapt resource value: 0x7f050000
public const int PhoneNumber = 2131034112;
TextView phoneNumberView =
this.FindViewById<TextView>
(Resource.Id.PhoneNumber);
The build process
generates a resource
You use the id to
access to the control

40. Dialogs
The AlertDialog class is used to display modal messages
var dialog = new AlertDialog.Builder(this);
dialog.SetTitle("Title");
dialog.SetMessage("Message Goes Here");
dialog.SetNegativeButton("No", (sender, args) => { });
dialog.SetNeutralButton("Maybe", (sender, args) => { });
dialog.SetPositiveButton("Yes", (sender, args) => { });
dialog.Show();

41. Intents
• Activities are decoupled: they aren’t directly connected.
• You can use Intents to exchange messages with the
operating system or with another activity
• Very similar concept to messages in the MVVM pattern

42. Intents to launch another activity
• You use an intent to redirect the user to another page of
the application
• You pass, as parameter, the type of the destination
activity
var intent = new Intent(this, typeof(CallDetailActivity));
this.StartActivity(intent);
Type of the activity to create

43. Intents to pass data to another activity
• You can use Extras to pass data from one activity to
another
Value
var intent = new Intent(this, typeof(CallDetailActivity));
intent.PutStringArrayListExtra("phone_numbers", new[] { phoneNumberText.Text});
this.StartActivity(intent);
Key
Different Put methods to
support various data types

44. Intent to retrieve data from another activity
• You get the parameter in the OnCreate() method of the Activity
class
• It’s exposed by the Intent object
public class CallDetailActivity : Activity
{
protected override void OnCreate(Bundle bundle)
{
IList<string> parameters = Intent.Extras.GetStringArrayList("phone_numbers");
}
}
Key
KeyValue

45. Intents to launch built-in activities
• The Intent class can be used to launch a built-in activity
• Use the Intent enumerator to choose the activity’s type
var callIntent = new Intent(Intent.ActionCall);
callIntent.SetData(Android.Net.Uri.Parse("tel:" + phoneNumber));
StartActivity(callIntent);

46. The activity’s lifecicle
• Active: the activity is visible and running
• Paused: the device is in sleep mode, it’s kept in memory
• Backgrounded: the activity is no more in foreground, it’s kept in
memory if possible
• Restarted: the activity is created from scratch

47. The activity’s lifecicle
The Activity class offers
multiple methods to
override to manage the
different states of the
activity’s lifecycle

48. Configuration changes
• Android destroys and recreate the activity every time the
configuration changes:
– Orientation change
– Keyboard displayed
– Device connected to a dock
• It’s important to save the state of the activity, in case a
configuration change happens

49. Activities
DEMO

50. La prima app
Xamarin.Forms

51. Domanda 1
Per mostrare del contenuto ad un utente devo usare il seguente
controllo:
a) Page
b) Intent
c) Activity
d) Dialog

52. Domanda 1
Per mostrare del contenuto ad un utente devo usare il seguente
controllo:
a) Page
b) Intent
c) Activity
d) Dialog

53. Domanda 2
Per navigare tra diverse Activities uso:
a) Pointer
b) Intent
c) Navigator
d) Arrow

54. Domanda 2
Per navigare tra diverse Activities uso:
a) Pointer
b) Intent
c) Navigator
d) Arrow

55. Domanda 3
Un’Activity è composta dalle seguenti due componenti:
a) HTML + Code Behind (Java)
b) XML + Code Behind (C#)
c) UML + links
d) XAML + Code Behind (C#)

56. Domanda 3
Un’Activity è composta dalle seguenti due componenti:
a) HTML + Code Behind (Java)
b) XML + Code Behind (C#)
c) UML + links
d) XAML + Code Behind (C#)

57. Saving state
DEMO

58. Managing lists

59. Displaying lists
• ListView and GridView are used to display collections of
data
• They rely on the concept of adapter
to define the data to display
• Adapters are pieces of code that
create the UI for a row

60. Adapters
var pn = new List<string>();
pn.Add("Title 1");
pn.Add("Title 2");
pn.Add("Title 3");

61. ArrayAdapter
ArrayAdapter is a built-in adapter to display a collection of
strings.
await client.GetCharactersForSeriesAsync();
List<string> list = response.Results.Select(x => x.Name).ToList();
ListView listView = this.FindViewById<ListView>(Resource.Id.Comics);
listView.Adapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1,
list);

62. Multiple layouts built-in
They are available using the enumerator
Android.Resource.Layout

63. Handling the selection
• Subscribe to the ItemClick event of the ListView
ListView listView = this.FindViewById<ListView>(Resource.Id.Comics);
listView.ItemClick += (sender, args) =>
{
...
};
listView.ItemClick += (sender, args) =>
{
string name = list[args.Position];
};

64. Lists
DEMO

65. La prima app
Xamarin.Forms

66. Domanda 1
Quali dei seguenti controlli possono essere utilizzati per mostrare una
lista?
a) ListView
b) ImageView
c) ComboBox
d) GridView

67. Domanda 1
Quali dei seguenti controlli possono essere utilizzati per mostrare una
lista?
a) ListView
b) ImageView
c) ComboBox
d) GridView

68. Domanda 2
Quali dei seguenti controlli possono essere utilizzati per mostrare una
lista?
a) ListView
b) ImageView
c) ComboBox
d) GridView

69. Domanda 2
Quali dei seguenti controlli possono essere utilizzati per mostrare una
lista?
a) ListView
b) ImageView
c) ComboBox
d) GridView

70. Custom adapters
• If you need to define a custom row layout, you need to use a
custom adapter
• A custom adapter needs to implement BaseAdapter<T>
• You need to implement the four required methods:
public abstract class BaseAdapter<T> : BaseAdapter
{
public abstract View GetView(int position, View convertView, ViewGroup parent);
public abstract T this[int position] { get; }
public abstract int Count { get; }
public abstract long GetItemId(int position);
}

71. LayoutInflator
• It’s a library class that takes the resource file and
returns a View hierarchy
• Every Activity has a LayoutInflator under the hood
<RelativeLayout ...>
<ImageView ... />
<TextView ... />
<TextView ... />
</RelativeLayout>

72. Creating a custom row
• The GetView() method of the custom adapter uses the
LayoutInflater to create the row starting from a layout
view = this.context.LayoutInflater.Inflate(Resource.Layout.CharacterRow,
parent, false);
<RelativeLayout ...>
<ImageView ... />
<TextView ... />
<TextView ... />
</RelativeLayout>

73. ListView Layout reuse
• ListView maintains the layouts only for the rows that are
visible to the user
• The GetView() method of the custom adapter will receive a
view to reuse if one is available
public override View GetView(int position, View convertView, ViewGroup parent)
{
//Cell reuse...
var view = convertView;
if (convertView == null)
{
view =
this.context.LayoutInflater.Inflate(Resource.Layout.CharacterRow, parent, false);
}
}

74. Custom lists
DEMO

75. La prima app
Xamarin.Forms

76. Domanda 1
Cosa devo implementare quando vado a realizzare un Custom
Adapter?
a) MyAdapter<T>
b) BaseAdapter<T>
c) CustomAdapter<T>
d) CommonAdapter<T>

77. Domanda 1
Cosa devo implementare quando vado a realizzare un Custom
Adapter?
a) MyAdapter<T>
b) BaseAdapter<T>
c) CustomAdapter<T>
d) CommonAdapter<T>

78. Working
with files

79. Files and folders
To create files and folder you can leverage the basic .NET APIs
(System.IO)
• Context.CacheDir
– Temporary files that can be deleted by the system anytime
• Context.ExternalCacheDir
– Temporary files that are removed when the app is deleted
• Android.OS.Environment.ExternalStorageDirectory.Path
– Access to external SD, it requires a capability in the manifest
• Environment.GetFolderPath(Environment.SpecialFolder.Per
sonal)
– Local storage of the application

80. Working with files
and folders
DEMO

81. Grazie per l’attenzione 
Guido Magrin
Xamarin Student Partner
@GuidoMagrin