Del via

Hello, Android Multiscreen: Quickstart

  • Artikkel

This two-part guide expands the Phoneword application to handle a second screen. Along the way, basic Android Application Building Blocks are introduced with a deeper dive into Android architecture.

In the walkthrough portion of this guide, you'll add a second screen to Phoneword application to keep track of the history of numbers translated using the app. The final application will have a second screen that displays the numbers that were "translated", as illustrated by the screenshot on the right:

Example app screenshots

The accompanying Deep Dive reviews what was built and discusses architecture, navigation, and other new Android concepts encountered along the way.

Requirements

Because this guide picks up where Hello, Android leaves off, it requires completion of the Hello, Android Quickstart.

Walkthrough

In this walkthrough you'll add a Translation History screen to the Phoneword application.

Start by opening the Phoneword application in Visual Studio and editing the Main.axml file from the Solution Explorer.

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.

Updating the layout

From the Toolbox, drag a Button onto the design surface and place it below the TranslatedPhoneWord TextView. In the Properties pane, change the button Id to @+id/TranslationHistoryButton

Drag a new button

Set the Text property of the button to @string/translationHistory. The Android Designer will interpret this literally, but you're going to make a few changes so that the button's text shows up correctly:

Set the translation history button text

Expand the values node under the Resources folder in the Solution Explorer and double-click the string resources file, Strings.xml:

Open Strings.xml

Add the translationHistory string name and value to the Strings.xml file and save it:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="translationHistory">Translation History</string>
    <string name="ApplicationName">Phoneword</string>
</resources>

The Translation History button text should update to reflect the new string value:

Button reflects new string value

With the Translation History button selected on the design surface, find the enabled setting in the Properties pane and set its value to false to disable the button. This will cause the button to become darker on the design surface:

Disable translation history button

Creating the second activity

Create a second Activity to power the second screen. In the Solution Explorer, right-click the Phoneword project and choose Add > New Item...:

Add a new file

In the Add New Item dialog, choose Visual C# > Activity and name the Activity file TranslationHistoryActivity.cs.

Replace the template code in TranslationHistoryActivity.cs with the following:

using System;
using System.Collections.Generic;
using Android.App;
using Android.OS;
using Android.Widget;
namespace Phoneword
{
    [Activity(Label = "@string/translationHistory")]
    public class TranslationHistoryActivity : ListActivity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            // Create your application here
            var phoneNumbers = Intent.Extras.GetStringArrayList("phone_numbers") ?? new string[0];
            this.ListAdapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1, phoneNumbers);
        }
    }
}

In this class, you're creating a ListActivity and populating it programmatically, so you don't need to create a new layout file for this Activity. This is discussed in more detail in the Hello, Android Multiscreen Deep Dive.

Adding a list

This app collects phone numbers (that the user has translated on the first screen) and passes them to the second screen. The phone numbers are stored as a list of strings. To support lists (and Intents, which are used later), add the following using directives to the top of MainActivity.cs:

using System.Collections.Generic;
using Android.Content;

Next, create an empty list that can be filled with phone numbers. The MainActivity class will look like this:

[Activity(Label = "Phoneword", MainLauncher = true)]
public class MainActivity : Activity
{
    static readonly List<string> phoneNumbers = new List<string>();
    ...// OnCreate, etc.
}

In the MainActivity class, add the following code to register the Translation History button (place this line after the translateButton declaration):

Button translationHistoryButton = FindViewById<Button> (Resource.Id.TranslationHistoryButton);

Add the following code to the end of the OnCreate method to wire up the Translation History button:

translationHistoryButton.Click += (sender, e) =>
{
    var intent = new Intent(this, typeof(TranslationHistoryActivity));
    intent.PutStringArrayListExtra("phone_numbers", phoneNumbers);
    StartActivity(intent);
};

Update the Translate button to add the phone number to the list of phoneNumbers. The Click handler for the translateButton should resemble the following code:

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

Save and build the application to make sure there are no errors.

Running the app

Deploy the application to an emulator or device. The following screenshots illustrate the running Phoneword application:

Example screenshots

Start by opening the Phoneword project in Visual Studio for Mac and editing the Main.axml file from the Solution Pad.

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.

Updating the layout

From the Toolbox, drag a Button onto the design surface and place it below the TranslatedPhoneWord TextView. In the Properties pad, change the button Id to @+id/TranslationHistoryButton:

Drag a new button

Set the Text property of the button to @string/translationHistory. The Android Designer will interpret this literally, but you're going to make a few changes so that the button's text shows up correctly:

Set the translation history button text

Expand the values node under the Resources folder in the Solution Pad and double-click the string resources file, Strings.xml:

Open Strings

Add the translationHistory string name and value to the Strings.xml file and save it:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="translationHistory">Translation History</string>
    <string name="ApplicationName">Phoneword</string>
</resources>

The Translation History button text should update to reflect the new string value:

Button reflects new string value

With the Translation History button selected on the design surface, open the Behavior tab in the Properties Pad and double-click the Enabled checkbox to disable the button. This will cause the button to become darker on the design surface:

Disable translation history button

Creating the second activity

Create a second Activity to power the second screen. In the Solution Pad, click the gray gear icon next to the Phoneword project and choose Add > New File...:

From the New File dialog, choose Android > Activity, name the Activity TranslationHistoryActivity, then click Add.

Replace the template code in TranslationHistoryActivity with the following:

using System;
using System.Collections.Generic;
using Android.App;
using Android.OS;
using Android.Widget;
namespace Phoneword
{
    [Activity(Label = "@string/translationHistory")]
    public class TranslationHistoryActivity : ListActivity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            // Create your application here
            var phoneNumbers = Intent.Extras.GetStringArrayList("phone_numbers") ?? new string[0];
            this.ListAdapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1, phoneNumbers);
        }
    }
}

In this class, a ListActivity is created and populated programmatically, so you don't have to create a new layout file for this Activity. This is explained in more detail in the Hello, Android Multiscreen Deep Dive.

Adding a list

This app collects phone numbers (that the user has translated on the first screen) and passes them to the second screen. The phone numbers are stored as a list of strings. To support lists (and Intents, which are used later), add the following using directives to the top of MainActivity.cs:

using System.Collections.Generic;
using Android.Content;

Next, create an empty list that can be filled with phone numbers. The MainActivity class will look like this:

[Activity(Label = "Phoneword", MainLauncher = true)]
public class MainActivity : Activity
{
    static readonly List<string> phoneNumbers = new List<string>();
    ...// OnCreate, etc.
}

In the MainActivity class, add the following code to register the TranslationHistory History button (place this line after the TranslationHistoryButton declaration):

Button translationHistoryButton = FindViewById<Button> (Resource.Id.TranslationHistoryButton);

Add the following code to the end of the OnCreate method to wire up the Translation History button:

translationHistoryButton.Click += (sender, e) =>
{
    var intent = new Intent(this, typeof(TranslationHistoryActivity));
    intent.PutStringArrayListExtra("phone_numbers", phoneNumbers);
    StartActivity(intent);
};

Update the Translate button to add the phone number to the list of phoneNumbers. The Click handler for the TranslateHistoryButton should resemble the following code:

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

Running the app

Deploy the application to an emulator or device. The following screenshots illustrate the running Phoneword application:

Example screenshots

Congratulations on completing your first multi-screen Xamarin.Android application! Now it's time to dissect the tools and skills you just learned – next up is the Hello, Android Multiscreen Deep Dive.