61. Android Implicit Intents – A Worked Example

In this chapter, an example application will be created in Android Studio designed to demonstrate a practical implementation of implicit intents. The goal will be to create and send an intent requesting that the content of a particular web page be loaded and displayed to the user. Since the example application itself will not contain an activity capable of performing this task, an implicit intent will be issued so that the Android intent resolution algorithm can be engaged to identify and launch a suitable activity from another application. This is most likely to be an activity from the Chrome web browser bundled with the Android operating system.

Having successfully launched the built-in browser, a new project will be created that also contains an activity capable of displaying web pages. This will be installed onto the device or emulator and used to demonstrate what happens when two activities match the criteria for an implicit...

61.1 Creating the Android Studio Implicit Intent Example Project

Select the Create New Project quick start option from the welcome screen and, within the resulting new project dialog, choose the Empty Activity template before clicking on the Next button.

Enter ImplicitIntent into the Name field and specify com.ebookfrenzy.implicitintent as the package name. Before clicking on the Finish button, change the Minimum API level setting to API 26: Android 8.0 (Oreo) and the Language menu to Kotlin.

61.2 Designing the User Interface

The user interface for the MainActivity class is very simple, consisting solely of a ConstraintLayout and a Button object. Within the Project tool window, locate the app -> res -> layout -> activity_main.xml file and double-click on it to load it into the Layout Editor tool.

Delete the default TextView and, with Autoconnect mode enabled, position a Button widget so that it is centered within the layout. Note that the text on the button (“Show Web Page”) has been extracted to a string resource named show_web_page.

Figure 61-1

With the Button selected use the Attributes tool window to configure the onClick property to call a method named showWebPage.

61.3 Creating the Implicit Intent

As outlined above, the implicit intent will be created and issued from within a method named showWebPage() which, in turn, needs to be implemented in the MainActivity class, the code for which resides in the MainActivity.kt source file. Locate this file in the Project tool window and double-click on it to load it into an editing pane. Once loaded, modify the code to add the showWebPage() method together with a few requisite imports:

package com.ebookfrenzy.implicitintent

 

import androidx.appcompat.app.AppCompatActivity

import android.os.Bundle

import android.content.Intent

import android.view.View

import android.net.Uri

 

class MainActivity : AppCompatActivity() {

 

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setContentView(R.layout...

61.4 Adding a Second Matching Activity

The remainder of this chapter will be used to demonstrate the effect of the presence of more than one activity installed on the device matching the requirements for an implicit intent. To achieve this, a second application will be created and installed on the device or emulator. Begin, therefore, by creating a new project within Android Studio with the application name set to MyWebView, using the same SDK configuration options used when creating the ImplicitIntent project earlier in this chapter and once again selecting an Empty Activity. Convert the project to use view bindings as outlined in section 18.8 Migrating a Project to View Binding.

61.5 Adding the Web View to the UI

The user interface for the sole activity contained within the new MyWebView project is going to consist of an instance of the Android WebView widget. Within the Project tool window, locate the activity_main.xml file, which contains the user interface description for the activity, and double-click on it to load it into the Layout Editor tool.

With the Layout Editor tool in Design mode, select the default TextView widget and remove it from the layout by using the keyboard delete key.

Drag and drop a WebView object from the Widgets section of the palette onto the existing ConstraintLayout view as illustrated in Figure 61-2:

Figure 61-2

Before continuing, change the ID of the WebView instance to webView1 and use the Infer constraints button to add any missing constraints.

61.6 Obtaining the Intent URL

When the implicit intent object is created to display a web browser window, the URL of the web page to be displayed will be bundled into the intent object within a Uri object. The task of the onCreate() method within the MainActivity class is to extract this Uri from the intent object, convert it into a URL string and assign it to the WebView object. To implement this functionality, modify the MainActivity.kt file so that it reads as follows:

package com.ebookfrenzy.mywebview

.

.

import java.net.URL

 

class MainActivity : AppCompatActivity() {

 

    private lateinit var binding: ActivityMainBinding

 

    override fun onCreate(savedInstanceState: Bundle?) {

.

.

        handleIntent()

    }

 

    private fun handleIntent() {

 

     &...

61.7 Modifying the MyWebView Project Manifest File

There are a number of changes that must be made to the MyWebView manifest file before it can be tested. In the first instance, the activity will need to seek permission to access the internet (since it will be required to load a web page). This is achieved by adding the appropriate permission line to the manifest file:

<uses-permission android:name="android.permission.INTERNET" />

Further, a review of the contents of the intent filter section of the AndroidManifest.xml file for the MyWebView project will reveal the following settings:

<intent-filter>

        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

In the above XML, the android.intent.action.MAIN entry indicates that this activity...

61.8 Installing the MyWebView Package on a Device

Before the MyWebView main activity can be used as the recipient of an implicit intent, it must first be installed onto the device. This is achieved by running the application in the normal manner. Because the manifest file contains neither the android.intent.action.MAIN nor the android.intent.category.LAUNCHER settings, Android Studio needs to be instructed to install, but not launch, the app. To configure this behavior, select the app -> Edit configurations… menu from the toolbar as illustrated in Figure 61-3:

Figure 61-3

Within the Run/Debug Configurations dialog, change the Launch option located in the Launch Options section of the panel to Nothing and click on Apply followed by OK:

Figure 61-4

With this setting configured run the app as usual. Note that the app is installed on the device, but not launched.

61.9 Testing the Application

In order to test MyWebView, simply re-launch the ImplicitIntent application created earlier in this chapter and touch the Show Web Page button. This time, however, the intent resolution process will find two activities with intent filters matching the implicit intent. As such, the system will display a dialog (Figure 61-5) providing the user with the choice of activity to launch.

Figure 61-5

Selecting the MyWebView option followed by the Just once button should cause the intent to be handled by our new MyWebView main activity, which will subsequently appear and display the designated web page.

If the web page loads into the Chrome browser without the above selection dialog appearing, it may be that Chrome has been configured as the default browser on the device. This can be changed by going to Settings -> Apps & notifications on the device followed by App info. Scroll down the list of apps and select Chrome. On the Chrome app info screen...

61.10 Summary

Implicit intents provide a mechanism by which one activity can request the service of another, simply by specifying an action type and, optionally, the data on which that action is to be performed. In order to be eligible as a target candidate for an implicit intent, however, an activity must be configured to extract the appropriate data from the inbound intent object and be included in a correctly configured manifest file, including appropriate permissions and intent filters. When more than one matching activity for an implicit intent is found during an intent resolution search, the user is prompted to make a choice as to which to use.

Within this chapter an example was created to demonstrate both the issuing of an implicit intent, and the creation of an example activity capable of handling such an intent.