Xamarin Android Native Development: Getting Started

Prerequisites

Before you begin, ensure you have the following installed:

• Visual Studio: With the .NET Desktop Development and Mobile Development with .NET workloads installed.
• Android SDK: Xamarin requires the Android SDK, which is typically installed with Visual Studio.
• Java Development Kit (JDK): Required by the Android SDK.

You can verify your installation by creating a new Xamarin.Android project in Visual Studio.

Step 1: Creating Your First Xamarin.Android Project

Visual Studio will create a basic Android project with essential files, including activities, layouts, and resources.

Step 2: Understanding Project Structure

A typical Xamarin.Android project has the following key folders:

• Properties: Contains project settings and assembly information.
• Resources: This is where you'll find UI layouts, drawables, strings, and styles.
  • layout: XML files defining the user interface for your activities.
  • drawable: Image assets for your app.
  • values: Contains strings, dimensions, and styles.
• Assets: For raw asset files like fonts or custom data.
• <YourActivityName>.cs: The C# code-behind file for your main activity.

Step 3: Designing Your User Interface

The main UI for an Android activity is defined in an XML file within the Resources/layout folder. The default template usually includes Main.axml.

Example: Modifying Main.axml

Open Resources/layout/Main.axml and you can use the visual designer or edit the XML directly. Let's add a button and a text view.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Hello, Xamarin!"
        android:textSize="24sp"
        android:gravity="center"
        android:id="@+id/textViewMessage" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Click Me"
        android:id="@+id/buttonAction"
        android:layout_marginTop="20dp" />
</LinearLayout>

The id attributes (e.g., @+id/textViewMessage) are crucial for referencing these UI elements in your C# code.

Step 4: Writing C# Code for Interaction

Now, let's make the button do something. Open the C# file for your main activity (e.g., MainActivity.cs).

using Android.App;
using Android.OS;
using Android.Widget;
using Android.Support.V7.App.AppCompatActivity; // Or AndroidX.AppCompat.App.AppCompatActivity
using Android.Util;

namespace MyFirstAndroidApp
{
    [Activity(Label = "MyFirstAndroidApp", MainLauncher = true, Icon = "@mipmap/icon")]
    public class MainActivity : AppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            // Get our UI elements from the layout
            TextView textViewMessage = FindViewById<TextView>(Resource.Id.textViewMessage);
            Button buttonAction = FindViewById<Button>(Resource.Id.buttonAction);

            // Attach an event handler to the button
            buttonAction.Click += (sender, e) =>
            {
                textViewMessage.Text = "Button Clicked!";
                Toast.MakeText(this, "Action successful!", ToastLength.Short).Show();
            };
        }
    }
}

In this code:

• SetContentView(Resource.Layout.Main); links the C# code to your XML layout.
• FindViewById<T>(Resource.Id.your_id); retrieves references to your UI elements.
• The Click event handler is attached to the button to execute code when tapped.

Step 5: Running Your Application

With your project set up and code written, you can now run the app:

1. Select a Target Device: In the Visual Studio toolbar, choose an Android emulator or a connected Android device from the device dropdown.
2. Run the Project: Click the green "Start" button or press F5.

Visual Studio will build the project, deploy it to the selected device/emulator, and launch your application. You should see the "Hello, Xamarin!" text and be able to click the button to change the text and show a toast message.