Hello, Android: Quickstart

In this two-part guide, you will build your first Xamarin.Android application (using Visual Studio or Visual Studio for Mac) and develop an understanding of the fundamentals of Android application development with Xamarin. Along the way, you will be introduced to the tools, concepts, and steps required to build and deploy a Xamarin.Android application.

Hello, Android Quickstart

In this walkthrough, you will create an application that translates an alphanumeric phone number (entered by the user) into a numeric phone number and display the numeric phone number to the user. The final application looks like this:

Screenshot of app when it is complete

Requirements

To follow along with this walkthrough, you will need the following:

  • Windows 7 or later.

  • Visual Studio 2015 Professional or later.

This walkthrough assumes that the latest version of Xamarin.Android is installed and running on your platform of choice. For a guide to installing Xamarin.Android, refer to the Xamarin.Android Installation guides. Before you get started, please download and unzip the Xamarin App Icons & Launch Screens set.

Configuring Emulators

If you are using Google's Android SDK emulator, we recommend that you configure the emulator to use hardware acceleration. Instructions for configuring hardware acceleration are available in Hardware Acceleration for Emulator Performance.

If you are using the Visual Studio Android Emulator, Hyper-V must be enabled on your computer. For more information about configuring the Visual Studio Android Emulator, see System Requirements for the Visual Studio Emulator for Android.

Walkthrough

Start Visual Studio. Click File > New > Project to create a new project.

In the New Project dialog, click the Android App template. Name the new project Phoneword. Click OK to create the new project:

New project is Phoneword

Creating the Layout

After the new project is created, expand the Resources folder and then the layout folder in the Solution Explorer. Double-click Main.axml to open it in the Android Designer. This is the layout file for the app's screen:

Open Main.axml

From the Toolbox (the area on the left), enter text into the search field and drag a Text (Large) widget onto the design surface (the area in the center):

Add large text widget

With the Text (Large) control selected on the design surface, use the Properties pane to change the text property of the Text (Large) widget to Enter a Phoneword: as shown here:

Set large text properties

Drag a Plain Text widget from the Toolbox to the design surface and place it underneath the Text (Large) widget:

Add plain text widget

With the Plain Text widget selected on the design surface, use the Properties pane to change the id property of the Plain Text widget to @+id/PhoneNumberText and change the text property to 1-855-XAMARIN:

Set plain text properties

Drag a Button from the Toolbox to the design surface and place it underneath the Plain Text widget:

Drag translate button to the design

With the Button selected on the design surface, use the Properties pane to change the id property of the Button to @+id/TranslateButton and change the text property to Translate:

Set translate button properties

Drag a TextView from the Toolbox to the design surface and place it under the Button widget. Set the id property of the TextView to @+id/TranslatedPhoneWord and change the text to an empty string:

Set the properties on the text view.

Save your work by pressing CTRL+S.

Writing Translation Code

The next step is to add some code to translate phone numbers from alphanumeric to numeric. Add a new file to the project by right-clicking the Phoneword project in the Solution Explorer pane and choosing Add > New Item... as shown below:

Add new item

In the Add New Item dialog, select Visual C# > Code > Code File and name the new code file PhoneTranslator.cs:

Add PhoneTranslator.cs

This creates a new empty C# class. Insert the following code into this file:

using System.Text;
using System;
namespace Core
{
    public static class PhonewordTranslator
    {
        public static string ToNumber(string raw)
        {
            if (string.IsNullOrWhiteSpace(raw))
                return "";
            else
                raw = raw.ToUpperInvariant();

            var newNumber = new StringBuilder();
            foreach (var c in raw)
            {
                if (" -0123456789".Contains(c))
                {
                    newNumber.Append(c);
                }
                else
                {
                    var result = TranslateToNumber(c);
                    if (result != null)
                        newNumber.Append(result);
                }
                // otherwise we've skipped a non-numeric char
            }
            return newNumber.ToString();
        }
        static bool Contains (this string keyString, char c)
        {
            return keyString.IndexOf(c) >= 0;
        }
        static int? TranslateToNumber(char c)
        {
            if ("ABC".Contains(c))
                return 2;
            else if ("DEF".Contains(c))
                return 3;
            else if ("GHI".Contains(c))
                return 4;
            else if ("JKL".Contains(c))
                return 5;
            else if ("MNO".Contains(c))
                return 6;
            else if ("PQRS".Contains(c))
                return 7;
            else if ("TUV".Contains(c))
                return 8;
            else if ("WXYZ".Contains(c))
                return 9;
            return null;
        }
    }
}

Save the changes to the PhoneTranslator.cs file by clicking File > Save (or by pressing CTRL+S), then close the file.

Wiring up the Interface

The next step is to add code to wire up the user interface by inserting backing code into the MainActivity class. Begin by wiring up the Translate button. In the MainActivity class, find the OnCreate method. The next step is to add the button code inside OnCreate, below the base.OnCreate(bundle) and SetContentView (Resource.Layout.Main) calls. First, modify the template code so that the OnCreate method resembles the following:

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

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

            // Set our view from the "main" layout resource
            SetContentView (Resource.Layout.Main);

            // New code will go here
        }
    }
}

Get a reference to the controls that were created in the layout file via the Android Designer. Add the following code inside the OnCreate method, after the call to SetContentView:

// Get our UI controls from the loaded layout
EditText phoneNumberText = FindViewById<EditText>(Resource.Id.PhoneNumberText);
TextView translatedPhoneWord = FindViewById<TextView>(Resource.Id.TranslatedPhoneWord);
Button translateButton = FindViewById<Button>(Resource.Id.TranslateButton);

Add code that responds to user presses of the Translate button. Add the following code to the OnCreate method (after the lines added in the previous step):

// Add code to translate number
translateButton.Click += (sender, e) =>
{
    // Translate user's alphanumeric phone number to numeric
    string translatedNumber = Core.PhonewordTranslator.ToNumber(phoneNumberText.Text);
    if (string.IsNullOrWhiteSpace(translatedNumber))
    {
        translatedPhoneWord.Text = string.Empty;
    }
    else
    {
        translatedPhoneWord.Text = translatedNumber;
    }
};

Save your work by selecting File > Save All (or by pressing CTRL-SHIFT-S) and build the application by selecting Build > Rebuild Solution (or by pressing CTRL-SHIFT-B).

If there are errors, go through the previous steps and correct any mistakes until the application builds successfully. If you get a build error such as, Resource does not exist in the current context, verify that the namespace name in MainActivity.cs matches the project name (Phoneword) and then completely rebuild the solution. If you still get build errors, verify that you have installed the latest Xamarin.Android updates.

Setting the Label and App Icon

You should now have a working application – it's time to add the finishing touches! In MainActivity.cs, edit the Label for the MainActivity. The Label is what Android displays at the top of the screen to let users know where they are in the application. At the top of the MainActivity class, change the Label to Phone Word as shown here:

namespace Phoneword
{
    [Activity (Label = "Phone Word", MainLauncher = true)]
    public class MainActivity : Activity
    {
        ...
    }
}

Now it's time to set the application icon. By default, Visual Studio will provide a default icon for the project. Let's delete these files from the solution, and replace them with a different icon. Expand the Resources folder in the Solution Pad. Notice that there are five folders that are prefixed with mipmap-, and that each of these folders contains a single Icon.png file:

mipmap- folders and Icon.png files

It is necessary to delete each of these icon files from the project. Right click on each of Icon.png files, and select Delete from the context menu:

Delete default Icon.png

Click on the Delete button in the dialog.

Next, download and unzip Xamarin App Icons set. This zip file holds the icons for the application. Each icon is visually identical but at different resolutions it renders correctly on different devices with different screen densities. The set of files must be copied into the Xamarin.Android project. In Visual Studio, in the Solution Explorer, right-click the mipmap-hdpi folder and select Add > Existing Items:

Add files

From the selection dialog, navigate to the unzipped Xamarin AdApp Icons directory and open the mipmap-hdpi folder. Select Icon.png and click Add.

Repeat these steps for each of the mipmap- folders until the contents of the mipmap- Xamarin App Icons folders are copied to their counterpart mipmap- folders in the Phoneword project.

After all the icons are copied to the Xamarin.Android project, open the Project Options dialog by right clicking on the project in the Solution Pad. Select Build > Android Application and select **@mipmap/icon** from the Application icon combo box:

Setting the project icon

Running the App

Finally, test the application by running it on an Android device or emulator and translating a Phoneword:

Screenshot of app when it is complete

Congratulations on completing your first Xamarin.Android application! Now it's time to dissect the tools and skills you have just learned. Next up is the Hello, Android Deep Dive.