Creating HelloWorld Program in Xamarin.Android

This tutorial explains step by step approach to create and deploy a Xamarin.Android application. For the sake of simplicity our first ever Xamarin.Android application, will have very basic user interface.

1. Creating a Xamarin.Android Application

This example assumes you already have Xamarin.Android installed in your development system. If you are a windows user you can use Visual Studio 2010 Professional or MonoDev IDE for development.

Let us create a new Xamarin.Android solution. Xamarin.Android includes several project templates, including:

1. Android Library Project – A reusable .NET library project for Android.
2. Android Application – A basic starter project with a single activity.
3. Android OpenGL Application – An OpenGL starter project.

We will use “Android Application template” for this example. Let’s create an application by doing the following:

2. Understanding Application Components

In the above section, we have just created a simple Xamarin.Android project. It automatically generates a project structure with different files and folders. The “HelloWorld” project includes three folders named Assets, Properties, and Resources.

• Assets – Contains any type of file the application needs included in its package. Files included here are accessible at runtime via the Assets class.
• Properties – Contains normal .NET assembly metadata.
• Resources – Contains application resources such as strings and images, as well as declarative XML user interface definitions. These resources are accessible through the generated Resource class.

The project template also created a class called HelloWorld in the file MainActivity.cs. An Activity is a class that models a destination where a user can perform some action while using an app, typically via a user interface.

3. Creating HelloWorld program

In this example we will create a simple screen with a TextView and a Button. Clicking the button will show a toast message to user.

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#ffe7e5e5">
    <TextView
        android:text="HelloWorld Example in Xamrin"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textView1"
        android:gravity="center_horizontal"
        android:layout_margin="10dp"
        android:textColor="#ff130c0c" />
    <Button
        android:id="@+id/myButton"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello"
        android:capitalize="characters"
        android:layout_margin="10dp"
        android:background="#ff0f37f5"
        android:textColor="#ffffffff"
        android:textSize="18dp"
        android:textStyle="bold"
        android:typeface="sans" />
</LinearLayout>

MainActivity.cs

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace HelloWorld
{
	[Activity (Label = "HelloWorld!", MainLauncher = true)]
	public class MainActivity : Activity
	{
		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);

			// Set your view layout layout resource file
			SetContentView (Resource.Layout.Main);

			// Initilize button from the layout resource
			Button button = FindViewById<Button> (Resource.Id.myButton);

			// and attach an event to it
			button.Click += delegate {
				//display toast message
				Toast.MakeText (Application, "Button Clicked!", ToastLength.Short).Show ();
			};
		}
	}
}