Shared user ID application example

Example of two Android applications signed with the same keystore and using the same sharedUserId.

The project contains two applications: Alice and Bob. Alice can start an activity from Bob and send a mesage.

##Setting up sharedUserId applications

The first step is to add the same android:sharedUserId property in the root element in AndroidManifest.xml of both applications:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="co.infinum.sharedprocess.alice"
    android:sharedUserId="co.infinum.sharedprocess">

Second step is to sign both applications with the same keystore.

Additionaly, if you wish to run both of the applications in the same process (this is not required), add the same android:process value to the application element in AndroidManifest.xml of both applications, for example:

<application
    android:icon="@drawable/icon"
    android:label="@string/app_name"
    android:process="com.test.app"
    >

##Starting an Activity from other Application

In order to start an Activity from other Application with the same shartedUserId use the following code:

/**
 * Fully qualified name of Bob's activity that will be started.
 */
private static final String BOBS_MAIN_ACTIIVTY = "co.infinum.sharedprocess.bob.MainActivity";

/**
 * Package identifier of Bob's application.
 */
private static final String BOBS_PACKAGE = "co.infinum.sharedprocess.bob";

/**
 * Key of the extra that will be passed to Bob's activity.
 */
private static final String EXTRA_SECRET_MESSAGE = "message";
    
public void tellSecretToBob(String message) {
  Intent intent = new Intent();
  intent.setComponent(new ComponentName(BOBS_PACKAGE, BOBS_MAIN_ACTIIVTY));
  intent.putExtra(EXTRA_SECRET_MESSAGE, message);
  startActivity(intent);
}

##Fetching resources from other Application

To fetch a resource from another application use the following method:

/**
 * Returns a resource identifier for a given resource name and type.
 *
 * @param resourceName name of the resource
 * @param resourceType type of the resource (e.g. drawable, string, layout...)
 * @return resource identifier or 0 if there is no such resource
 */
public int getBobsResource(String resourceName, String resourceType) {
  PackageManager pm = getPackageManager();

  Resources resources = null;
  if (pm != null) {
    try {
      resources = pm.getResourcesForApplication(BOBS_PACKAGE);

      int res = resources.getIdentifier(resourceName, resourceType, BOBS_PACKAGE);
    } catch (PackageManager.NameNotFoundException e) {
      e.printStackTrace();
    }
  }

  return 0;
}