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Hello, Android: Quickstart

  • Artikkeli

In this two-part guide, you will build your first Xamarin.Android application with Visual Studio and develop an understanding of the fundamentals of Android application development with Xamarin.

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 phone number translation app when it is complete.

Windows requirements

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

  • Windows 10.

  • Visual Studio 2019 or Visual Studio 2017 (version 15.8 or later): Community, Professional, or Enterprise.

macOS requirements

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

  • The latest version of Visual Studio for Mac.

  • A Mac running macOS High Sierra (10.13) 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.

Configuring emulators

If you are using the Android 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.

Create the project

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 and click OK:

New project is Phoneword

In the New Android App dialog, click Blank App and click OK to create the new project:

Select the Blank App template

Create a layout

Tip

Newer releases of Visual Studio support opening .xml files inside the Android Designer.

Both .axml and .xml files are supported in the Android Designer.

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

Open activity axml file

Tip

Newer releases of Visual Studio contain a slightly different app template.

  1. Instead of activity_main.axml, the layout is in content_main.axml.
  2. The default layout will be a RelativeLayout. For the rest of the steps on this page to work you should change the <RelativeLayout> tag to <LinearLayout> and add another attribute android:orientation="vertical" to the LinearLayout opening tag.

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::

Set large text properties

Drag a Plain Text widget from the Toolbox to the design surface and place it underneath the Text (Large) widget. Placement of the widget will not occur until you move the mouse pointer to a place in the layout that can accept the widget. In the screenshots below, the widget cannot be placed (as seen on the left) until the mouse pointer is moved just below the previous TextView (as shown on the right):

Mouse indicates where widget can be placed

When the Plain Text (an EditText widget) is placed correctly, it will appear as illustrated in the following screenshot:

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 its Text property to Translate and its Id property to @+id/TranslateButton:

Set translate button properties

Drag a TextView from the Toolbox to the design surface and place it under the Button widget. Change the Text property of the TextView to an empty string and set its Id property to @+id/TranslatedPhoneword:

Set the properties on the text view.

Save your work by pressing CTRL+S.

Write some 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.

Wire up the user 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(savedInstanceState) and SetContentView(Resource.Layout.activity_main) calls. First, modify the template code so that the OnCreate method resembles the following:

using Android.App;
using Android.OS;
using Android.Support.V7.App;
using Android.Runtime;
using Android.Widget;

namespace Phoneword
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.activity_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 Visual Studio updates.

Set the app name

You should now have a working application – it's time to set the name of the app. Expand the values folder (inside the Resources folder) and open the file strings.xml. Change the app name string to Phone Word as shown here:

<resources>
    <string name="app_name">Phone Word</string>
    <string name="action_settings">Settings</string>
</resources>

Run the app

Test the application by running it on an Android device or emulator. Tap the TRANSLATE button to translate 1-855-XAMARIN into a phone number:

Screenshot of app running

To run the app on an Android device, see how to set up your device for development.

Launch Visual Studio for Mac from the Applications folder or from Spotlight.

Click New Project... to create a new project.

In the Choose a template for your new project dialog, click Android > App and select the Android App template. Click Next.

Choose the Android App template

In the Configure your Android app dialog, name the new app Phoneword and click Next.

Configure the Android App

In the Configure your new Android App dialog, leave the Solution and Project names set to Phoneword and click Create to create the project.

Create a layout

Tip

Newer releases of Visual Studio support opening .xml files inside the Android Designer.

Both .axml and .xml files are supported in the Android Designer.

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

Open Main.axml

Select the Hello World, Click Me! Button on the design surface and press the Delete key to remove it.

From the Toolbox (the area on the right), 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) widget selected on the design surface, you can use the Properties pad to change the Text property of the Text (Large) widget to Enter a Phoneword: as shown below:

Set large text widget properties

Next, drag a Plain Text widget from the Toolbox to the design surface and place it underneath the Text (Large) widget. Notice that you can use the search field to help locate widgets by name:

Add plain text widget

With the Plain Text widget selected on the design surface, you can use the Properties pad 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 widget properties

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

Add a button

With the Button selected on the design surface, you can use the Properties pad to change the Id property of the Button to @+id/TranslateButton and change the Text property to Translate:

Configure as the translate button

Drag a TextView from the Toolbox to the design surface and place it under the Button widget. With the TextView selected, 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 ⌘ + S.

Write some code

Now, add some code to translate phone numbers from alphanumeric to numeric. Add a new file to the project by clicking the gear icon next to the Phoneword project in the Solution pad and choosing Add > New File...:

Add a new file to the project

In the New File dialog, select General > Empty Class, name the new file PhoneTranslator, and click New. This creates a new empty C# class for us.

Remove all of the template code in the new class and replace it with the following code:

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 choosing File > Save (or by pressing ⌘ + S), then close the file. Ensure that there are no compile-time errors by rebuilding the solution.

Wire up the user interface

The next step is to add code to wire up the user interface by adding the backing code into the MainActivity class. Double-click MainActivity.cs in the Solution Pad to open it.

Begin by adding an event handler to the Translate button. In the MainActivity class, find the OnCreate method. Add the button code inside OnCreate, below the base.OnCreate(bundle) and SetContentView (Resource.Layout.Main) calls. Remove any existing button handling code (i.e., code that references Resource.Id.myButton and creates a click handler for it) so that the OnCreate method resembles the following:

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
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);

            // Our code will go here
        }
    }
}

Next, a reference is needed to the controls that were created in the layout file with 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 by adding the following code to the OnCreate method (after the lines added in the last step):

// Add code to translate number
string translatedNumber = string.Empty;

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

Save your work and build the application by selecting Build > Build All (or by pressing ⌘ + B). If the application compiles, you will get a success message at the top of Visual Studio for Mac:

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 and Visual Studio for Mac updates.

Set the label and app icon

Now that you have a working application, it's time to add the finishing touches! Start by editing the Label for 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 for Mac will provide a default icon for the project. 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 Remove 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 for Mac, in the Solution Pad, right-click the mipmap-hdpi folder and select Add > Add Files:

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 Open.

In the Add File to Folder dialog box, select Copy the file into the directory and click OK:

Copy the file to the directory dialog

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

Run 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

To run the app on an Android device, see how to set up your device for development.

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.