81. An Android Studio App Links Tutorial

The goal of this chapter is to provide a practical demonstration of both Android app links and the Android Studio App Link Assistant.

This chapter will add app linking support to an existing Android app, allowing an activity to be launched via an app link URL. In addition to launching the activity, the content displayed will be specified within the path of the URL.

81.1 About the Example App

The project used in this chapter is named AppLinking and is a basic app designed to allow users to find out information about landmarks in London. The app uses a SQLite database accessed through a standard Android content provider class. The app is provided with an existing database containing a set of records for some popular tourist attractions in London. In addition to the existing database entries, the app also lets the user add and delete landmark descriptions.

In its current form, the app allows the existing records to be searched and new records to be added and deleted.

The project consists of two activities named AppLinkingActivity and LandmarkActivity. AppLinkingActivity is the main activity launched at app startup. This activity allows the user to enter search criteria and to add additional records to the database. When a search locates a matching record, LandmarkActivity launches and displays the information for the related landmark.

...

81.2 The Database Schema

The data for the example app is contained within a file named landmarks.db located in the app -> assets –> databases folder of the project hierarchy. The database contains a single table named locations, the structure of which is outlined in Table 81-5:

81.3 Loading and Running the Project

The project is contained within the AppLinking folder of the sample source code download archive located at the following URL:

https://www.ebookfrenzy.com/retail/androidstudio41/index.php

Having located the folder, open it within Android Studio and run the app on a device or emulator. Once the app is launched, the screen illustrated in Figure 81-1 below will appear:

Figure 81-1

As currently implemented, landmarks are located using the ID for the location. The default database configuration currently contains two records referenced by the IDs “londonbridge” and “toweroflondon”. Test the search feature by entering londonbridge into the ID field and clicking the Find button. When a matching record is found, the second activity (LandmarkActivity) is launched and passed information about the record to be displayed. This information takes the form of extra data added to the Intent object. This information is...

81.4 Adding the URL Mapping

Now that the app has been loaded into Android Studio and tested, the project is ready for the addition of app link support. The objective is for the LandmarkActivity screen to launch and display information in response to an app link click. This is achieved by mapping a URL to LandmarkActivity. For this example, the format of the URL will be as follows:

http://<website domain>/landmarks/<landmarkId>

When all of the steps have been completed, the following URL should, for example, cause the app to display information for the Tower of London:

http://www.yourdomain.com/landmarks/toweroflondon

To add a URL mapping to the project, begin by opening the App Links Assistant using the Tools -> App Links Assistant menu option. Once open, the assistant should appear as shown in Figure 81-3:

Figure 81-3

Click on the Open URL Mapping Editor button to begin mapping a URL to an activity. Within the mapping screen, click on the ‘...

81.5 Adding the Intent Filter

As explained in the previous chapter, an intent filter is needed to allow the target activity to be launched in response to an app link click. In fact, when the URL mapping was added, the intent filter was automatically added to the project manifest file. With the URL mapping selected in the App Links Assistant URL mapping list, scroll down the screen until the intent filter Preview section comes into view. The preview should contain the modified AndroidManifest.xml file with the newly added intent filters included:

Figure 81-7

81.6 Adding Intent Handling Code

The steps taken so far ensure that the correct activity is launched in response to an appropriately formatted app link URL. The next step is to handle the intent within the LandmarkActivity class so that the correct record is extracted from the database and displayed to the user. Before making any changes to the code within the LandmarkActivity.java file, it is worthwhile reviewing some areas of the existing code. Open the LandmarkActivity.java file in the code editor and locate the onCreate() and handleIntent() methods which should currently read as follows:

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_landmark);

 

    titleText = findViewById(R.id.titleText);

    descriptionText = findViewById(R.id.descriptionText);

    deleteButton...

81.7 Testing the App Link

Test that the intent handling works by selecting a suitable device or emulator in the toolbar as the deployment target, returning to the App Links Assistant panel and clicking on the Test App Links button. When prompted for a URL to test, enter the URL (using the domain referenced in the app link mapping) for the londonbridge landmark ID before clicking on the Run Test button:

Figure 81-9

Before the activity appears, it is likely that Android will display a panel (Figure 81-10) within which a choice needs to be made as to how the app link is to be handled:

Figure 81-10

Until the app link has been associated with a web site, Android will display this selection panel every time the activity is launched using a View intent action unless the user selects the Always option.

81.8 Associating an App Link with a Web Site

As outlined in the previous chapter, an app link may be associated with a web site by creating a Digital Asset Links file and installing it on the web site. Although the steps to generate this file will be covered in this chapter, it will only be possible to test these instructions using your own app (with a unique application ID) and if you have access to an https based web server onto which the assets file can be installed.

To generate the Digital Asset Links file, display the App Links Assistant and click on the Open Digital Asset Links File Generator button. This will display the panel shown in Figure 81-11:

Figure 81-11

Enter the URL of the site onto which the assets file is to be uploaded and verify that the application ID matches the package name. Choose either a keystore file containing the SHA signing key for your project, or use the menu to select either the release or debug signing configuration as used by Android...

81.9 Summary

This chapter has demonstrated the steps involved in implementing App Link support within an Android app project. Areas covered in this chapter include the use of the App Link Assistant in Android Studio, App Link URL mapping, intent filters, handling website association using Digital Asset File entries and App Link testing.

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Neil Smyth

Neil Smyth has over 25 years of experience in the IT industry, including roles in software development and enterprise-level UNIX and Linux system administration. In addition to a bachelor’s degree in information technology, he also holds A+, Security+, Network+, Project+, and Microsoft Certified Professional certifications and is a CIW Database Design Specialist. Neil is the co-founder and CEO of Payload Media, Inc. (a technical content publishing company), and the author of the Essentials range of programming and system administration books.
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Column	Type	Description
_id	String	The primary index, this column contains string values that uniquely identify the landmarks in the database.
Title	String	The name of the landmark (e.g. London Bridge).
description	String	A description of the landmark.
personal	Boolean	Indicates whether the record is personal...

81.3 Loading and Running the Project

The project is contained within the AppLinking folder of the sample source code download archive located at the following URL:

https://www.ebookfrenzy.com/retail/androidstudio41/index.php

Having located the folder, open it within Android Studio and run the app on a device or emulator. Once the app is launched, the screen illustrated in Figure 81-1 below will appear:

Figure 81-1

As currently implemented, landmarks are located using the ID for the location. The default database configuration currently contains two records referenced by the IDs “londonbridge” and “toweroflondon”. Test the search feature by entering londonbridge into the ID field and clicking the Find button. When a matching record is found, the second activity (LandmarkActivity) is launched and passed information about the record to be displayed. This information takes the form of extra data added to the Intent object. This information is...

81.4 Adding the URL Mapping

Now that the app has been loaded into Android Studio and tested, the project is ready for the addition of app link support. The objective is for the LandmarkActivity screen to launch and display information in response to an app link click. This is achieved by mapping a URL to LandmarkActivity. For this example, the format of the URL will be as follows:

http://<website domain>/landmarks/<landmarkId>

When all of the steps have been completed, the following URL should, for example, cause the app to display information for the Tower of London:

http://www.yourdomain.com/landmarks/toweroflondon

To add a URL mapping to the project, begin by opening the App Links Assistant using the Tools -> App Links Assistant menu option. Once open, the assistant should appear as shown in Figure 81-3:

Figure 81-3

Click on the Open URL Mapping Editor button to begin mapping a URL to an activity. Within the mapping screen, click on the ‘...

81.5 Adding the Intent Filter

As explained in the previous chapter, an intent filter is needed to allow the target activity to be launched in response to an app link click. In fact, when the URL mapping was added, the intent filter was automatically added to the project manifest file. With the URL mapping selected in the App Links Assistant URL mapping list, scroll down the screen until the intent filter Preview section comes into view. The preview should contain the modified AndroidManifest.xml file with the newly added intent filters included:

Figure 81-7

81.6 Adding Intent Handling Code

The steps taken so far ensure that the correct activity is launched in response to an appropriately formatted app link URL. The next step is to handle the intent within the LandmarkActivity class so that the correct record is extracted from the database and displayed to the user. Before making any changes to the code within the LandmarkActivity.java file, it is worthwhile reviewing some areas of the existing code. Open the LandmarkActivity.java file in the code editor and locate the onCreate() and handleIntent() methods which should currently read as follows:

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_landmark);

 

    titleText = findViewById(R.id.titleText);

    descriptionText = findViewById(R.id.descriptionText);

    deleteButton...

81.7 Testing the App Link

Test that the intent handling works by selecting a suitable device or emulator in the toolbar as the deployment target, returning to the App Links Assistant panel and clicking on the Test App Links button. When prompted for a URL to test, enter the URL (using the domain referenced in the app link mapping) for the londonbridge landmark ID before clicking on the Run Test button:

Figure 81-9

Before the activity appears, it is likely that Android will display a panel (Figure 81-10) within which a choice needs to be made as to how the app link is to be handled:

Figure 81-10

Until the app link has been associated with a web site, Android will display this selection panel every time the activity is launched using a View intent action unless the user selects the Always option.

81.8 Associating an App Link with a Web Site

As outlined in the previous chapter, an app link may be associated with a web site by creating a Digital Asset Links file and installing it on the web site. Although the steps to generate this file will be covered in this chapter, it will only be possible to test these instructions using your own app (with a unique application ID) and if you have access to an https based web server onto which the assets file can be installed.

To generate the Digital Asset Links file, display the App Links Assistant and click on the Open Digital Asset Links File Generator button. This will display the panel shown in Figure 81-11:

Figure 81-11

Enter the URL of the site onto which the assets file is to be uploaded and verify that the application ID matches the package name. Choose either a keystore file containing the SHA signing key for your project, or use the menu to select either the release or debug signing configuration as used by Android...

81.9 Summary

This chapter has demonstrated the steps involved in implementing App Link support within an Android app project. Areas covered in this chapter include the use of the App Link Assistant in Android Studio, App Link URL mapping, intent filters, handling website association using Digital Asset File entries and App Link testing.