Building your first android app using Xamarin

Building your first Android
app using Xamarin
Gill Cleeren - @gillcleeren

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

I’m a Pluralsight author!
• Courses on Windows 8, social and HTML5
• http://gicl.me/mypscourses

Agenda
• Overview of Xamarin and Xamarin.Android
• Xamarin.Android fundamentals
• Creating a detail screen
• Lists and navigation
• Navigating from master to detail
• (Optional) Intro to using Fragments
• Optimizing the application
• Preparing for store deployment

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

The demo scenario
• Android Coffee Store Manager
• List of coffee
• Navigation to details page

DEMO
Looking at the finished application

Overview of Xamarin and
Xamarin.Android

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

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

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

Xamarin.Android exposes many extra device
types

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

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

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

Target architecture for a Xamarin app

Preparing for
Android development

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...)

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

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

Developing with a device
• 3 steps
• Enable Debugging on the Device
• Install USB Drivers (Windows only)
• Connect the Device to the Computer

Enable device debugging
• Tap the Build number 7 times to reveal
developer options

DEMO
A quick look at the development setup

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

• 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

• One activity needs to be the “entry point” for the app:
MainLauncher=True

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

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

The designer for Xamarin.Android views

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

• 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

• Once we have created the controls, we can access them from code
• Field name is used for lookup

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

DEMO
Creating our first Android application together!

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

Fundamental #4: ListViews and adapters

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

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);
}
}

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

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
}

DEMO
Adding a ListView and an adapter

Customizing the ListView with other row views

DEMO
Using the built-in row views

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…

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: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>

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;
}

DEMO
Adding our own custom row view

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

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

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);

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);
}

DEMO
Navigating from the List
to the Detail page

The need for Fragments
• Larger screen: more complex to build UIs that look good on all
screens
• Layouts which look good on a small screen may not look good on a large
tablet screen
• Android V3.0 introduced Fragments
• Fragment is a UI module
• UI gets divided into reusable parts
• Each “part” is an separate activity
• At run time, the Activities themselves will decide which Fragments to use
• Also work in older versions through Support packages

FragmentManager
• To help an Activity coordinate and manage all these Fragments,
Android introduced a new class called the FragmentManager
• Each activity has an instance of the FragmentManager
• Allows finding, adding and removing fragments

Adding a fragment to an Activity
• We can add the Fragment to the Activity in 2 ways
• Declaratively:
• Fragments can be used declaratively within .axml layout files by using the <Fragment>
tag
• Programmatically
• Fragments can also be instantiated dynamically by using the FragmentManager class’s
API

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:id="@+id/CoffeeNameLabel" />

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

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

DEMO
Adding resources
and drawables to the application

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

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

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Building your first android app using Xamarin

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