So, I followed the official guide here https://developer.android.com/training/auto/start/index.html to create a very basic Android Auto Audio App. For the moment it does nothing, other then declaring what needs to be declared in the manifest and implementing empty onGetRoot() and onLoadChildren().
Problem is, that it is not being recognized by the Android Auto app.
Any idea where to get a working example? What could be wrong?
Manifest:
<service
android:name=".MyService"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name=
"android.media.browse.MediaBrowserService"/>
</intent-filter>
</service>
automotive_app_desc.xml:
<automotiveApp>
<uses name="media" />
</automotiveApp>
service:
public class MyService extends MediaBrowserServiceCompat {
public static final String MEDIA_ID_ROOT = "__ROOT__";
#Override
public BrowserRoot onGetRoot(String clientPackageName, int clientUid,
Bundle rootHints) {
//TODO: check if the client is allow access
return new BrowserRoot(MEDIA_ID_ROOT, null);
}
#Override
public void onLoadChildren(final String parentMediaId,
final Result<List<MediaBrowserCompat.MediaItem>> result) {
// Assume for example that the music catalog is already loaded/cached.
List<MediaBrowserCompat.MediaItem> mediaItems = new ArrayList<>();
// Check if this is the root menu:
if (MEDIA_ID_ROOT.equals(parentMediaId)) {
// build the MediaItem objects for the top level,
// and put them in the mediaItems list
} else {
// examine the passed parentMediaId to see which submenu we're at,
// and put the children of that menu in the mediaItems list
}
result.sendResult(mediaItems);
}
You have to go to Android Auto settings, tap many times on the Version entry (the last one) to unlock Developer settings. Then tap on Developer settings menu item and enable Unknown sources. Restart Android Auto and if your app it's ok it will be listed. Worked for me
I didn't see this included in your snippet from the manifest, but double check that this line is also there.
<application>
...
<meta-data android:name="com.google.android.gms.car.application"
android:resource="#xml/automotive_app_desc"/>
...
</application>
I created a sample app matching everything you have (plus the line above), and it appears in Android Auto on the mobile device, as well as the Desktop Head Unit.
Related
I have an app that's using Branch.io and am in process of updating it to support Instant Apps. Part of this change will require using app links to navigate from one part of app to another.
The Activity that I'm opening is configured to use Branch.io (e.g. using instructions in https://dev.branch.io/marketing-channels/android-instant-apps/guide/) and includes following in it's onStart() method. However I'm not seeing parameters I'm including in deep link in referringParams.
Branch.getInstance().initSession(new Branch.BranchReferralInitListener() {
#Override
public void onInitFinished(JSONObject referringParams, BranchError error) {
Log.d("Branch", "onInitFinished() with deep link data: " + referringParams);
}
});
Do I need to trigger opening of the branch link in particular way from Android code for this to work?
BTW referringParams above does show +clicked_branch_link being false.
UPDATE
Just to clarify a few things. I'm trying for example to launch ActivityB from ActivityA using app deep link. ActivityB includes <intent-filter> as described in https://dev.branch.io/marketing-channels/android-instant-apps/guide/ for example. In ActivityA I'm currently trying to open/create Branch.io link as follows (have also formed link directly, as is used in that android-instant-apps sample for example, but that's not considered a "branch link")
HashMap<String, String> metadata = new HashMap<>();
metadata.put(PARAM, param);
BranchUniversalObject branchUniversalObject = new BranchUniversalObject().addContentMetadata(metadata);
LinkProperties linkProperties = new LinkProperties();
branchUniversalObject.generateShortUrl(context, linkProperties, (url, error) -> {
if (error == null) {
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
context.startActivity(intent);
}
});
If I try to open the url generated (by generateShortUrl) directly on device (clicking on link for example) then ActivityB is launched and I see the param I included in initSession callback. If I try to open it using code above (navigating betweeen ActivityA and ActivityB then ActivityB is launched but don't get the params (and +clicked_branch_link is false)
Sojan from Branch here
If you are trying to deep link to a new feature from another instant app apk unfortunetely Branch is not supporting this feature now.
If you are trying to get deep link params on opening an activity B in a new feature from activity A from another feature in an installed app you can achieve it in the following way.
ActivityA.java
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("yourBranchLink"));
intent.putExtra("branch","yourBranchLink");
intent.putExtra("branch_force_new_session",true);
Hope this helps
In order to configure the Branch SDK with your Instant App supported Android App you can follow the steps below:
1. Initialize the Branch SDK
Initialize the Branch SDK in the onCreate() method of your Application class. If you plan on deep linking from your Android Instant App to your full Android app after its installed, you'll need to add the line enablePlayStoreReferrer. This adds a delay to the initialization to wait for the Google Play Referrer, which can take up to a second.
public void onCreate() {
super.onCreate();
// This is needed to deferred deep link from an Android Instant App to a full app
// It tells the Branch initialization to wait for the Google Play Referrer before proceeding.
Branch.enablePlayStoreReferrer(1000L);
// Initialize the Branch SDK
Branch.getAutoInstance(this);
}
2. Add your Branch keys and register for Install Referrer
Instant Apps can be rather confusing as there are many different manifests, but you want to find the Manifest that contains your application tags. Make sure your Application class name is defined here, and then specify the Branch keys inside the application element.
<application
android:allowBackup="true"
android:label="#string/app_name"
android:theme="#style/AppTheme"
android:supportsRtl="true"
android:name=".MyApplication">
<!-- Set to true to use Branch_Test_Key -->
<meta-data android:name="io.branch.sdk.TestMode" android:value="false" />
<meta-data android:name="io.branch.sdk.BranchKey" android:value="key_live_app_live_key" />
<meta-data android:name="io.branch.sdk.BranchKey.test" android:value="key_test_app_test_key" />
<receiver android:name="io.branch.referral.InstallListener" android:exported="true">
<intent-filter>
<action android:name="com.android.vending.INSTALL_REFERRER" />
</intent-filter>
</receiver>
</application>
3. Configure your Branch links as Android App Links
Assuming you've already configured Branch for Android App Links for your Android App the next step is to add the intent filter for App links support in your Application Tag. Make sure to replace the xxxx with your link Domain. (If you haven't configured your full native app to use Branch as Android App Links you can follow the steps mentioned here and here.)
<application
......
<intent-filter android:autoVerify="true">
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="https" android:host="xxxx.app.link" />
<data android:scheme="https" android:host="xxxx-alternate.app.link" />
</intent-filter>
</application>
4. Retrieve Branch deep link data
Add Branch initSession in Activities which are configured to open from a link click in order to receive the deep link params. This will return the deep link data from the referring link.
protected void onStart() {
super.onStart();
Branch.getInstance().initSession(new Branch.BranchReferralInitListener() {
#Override
public void onInitFinished(JSONObject referringParams, BranchError error) {
Log.d("Branch","onInitFinished() with deep link data: " + referringParams);
}
});
}
5. Configure the deep linking from Instant App to your Full App
To convert your user who just arrived in your Instant App to your full native app, Branch SDK provides convenient methods to check for app types and full app conversion. This eliminates the dependency on Google IA support SDK ('com.google.android.instantapp'). Here are some of the methods:
Branch.isInstantApp()
This convenience method checks whether the current version of app running is Instant App or Full Android App
Branch.showInstallPrompt()
This methods shows an install prompt for the full Android app, allowing you an easy way to pass Branch referring deep data to the full app through the install process.
I want to create an android app which will "scan" other applications'layouts and find out if there are buttons etc.
Some apps, like whatsapp, doesn't allow third parts to move into the app, so I though that using accessibility could be the solution.
Now the problem is that I've never used Accessibility, so can someone of you can please show me how to "scan" an app's layout to find buttons?
Thanks a lot
What you're looking for is an Accessibility Service. Configuring an accessibility service is somewhat complicated. I have set up a repository of accessibility boilerplate code that sets up an AccessibilityService that logs the node heirarchy to LogCat, and has the default project settings activity set up as it's settings activity. Here are some of the highlights, as I dislike just posting github repos as answers. Note that I use a lot of my own libraries. CLog is a logging library and AndroidAccessibilityUtils wraps node infos with some common utility functions. You can find references to the dependencies in the build.gradle file on the github repo at the bottom. Here are some code highlights.
Your manifest.xml file is going to be significantly different from an Activity, and should contain an entry like this in your Application element:
<application .... >
...
<service
android:name="com.moba11y.basicaccessibilityservice.BasicAccessibilityService"
android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE" >
<intent-filter>
<action android:name="android.accessibilityservice.AccessibilityService" />
</intent-filter>
<meta-data
android:name="android.accessibilityservice"
android:resource="#xml/service_config" />
</service>
...
</application>
First you need to create a subclass of Accessibility Service:
public class BasicAccessibilityService extends AccessibilityService {
static {
CLog.initialize(BasicAccessibilityService.class.getSimpleName(), BuildConfig.DEBUG);
}
#Override
public void onAccessibilityEvent(AccessibilityEvent event) {
CLog.d(event.toString());
switch (event.getEventType()) {
//On Gesture events print out the entire view heirarchy!
case AccessibilityEvent.TYPE_GESTURE_DETECTION_START:
CLog.d(A11yNodeInfo.wrap(getRootInActiveWindow()).toViewHeirarchy());
default: {
//If the event has a source, let's print it out separately.
if (event.getSource() != null) {
CLog.d(A11yNodeInfo.wrap(event.getSource()).toViewHeirarchy());
}
}
}
}
#Override
public void onInterrupt() {
CLog.e("Service Interrupted: Have never actually had this happen.");
}
}
That is the bulk of the highlights. You also should have a "service_config" XML with properties, as is referenced in the changes to the Manifest XML file. More details, and a reasonable starer point can be found in the open source repo on GitHub.
https://github.com/chriscm2006/Android-Accessibility-Service-Boilerplate
I am facing a problem in override the On Click Behavior in Appboy deeplink
Please find the following data
1- Register Appboy in BaseActivity which is the parent activity for all Application Activities
#Override
protected void onResume() {
AppboyInAppMessageManager.getInstance().registerInAppMessageManager(this);
Appboy.getInstance(this).requestInAppMessageRefresh();
}
#Override
protected void onPause() {
AppboyInAppMessageManager.getInstance().unregisterInAppMessageManager(this);
}
2- Add the receivers in Manifest File as following
<receiver android:name="com.forsale.forsale.appboy.AppboyGcmReceiver"
android:permission="com.google.android.c2dm.permission.SEND" >
<intent-filter>
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
<action android:name="com.google.android.c2dm.intent.REGISTRATION" />
<category android:name="com.forsale.forsale" />
</intent-filter>
</receiver>
<receiver
android:name="com.forsale.forsale.appboy.AppBoyOpenReceiver"
android:exported="false" >
<intent-filter>
<action android:name="com.forsale.forsale.intent.APPBOY_PUSH_RECEIVED" />
<action android:name="com.forsale.forsale.intent.APPBOY_NOTIFICATION_OPENED" />
</intent-filter>
</receiver>
Know I can send in app message using app boy dashboard, and receive the message, but when I click the message it open appboy web activity with the link
I need to override this behaviour to be able to get the link that I sent in In app message and parse some parameters from it and direct the use to an activity inside my app
I have tried the following
remove default app boy web activity from manifest file /// the app crash
implement the IInAppMessageManagerListener /// the app stop receiving any messages
Please note that the application call the onReceive method when trying to register appboy and print the log (action = REGISTRATION, RegId = "..."), but it never lo any other actions like RECEIVE, or OPEN
public void onReceive(Context context, Intent intent) {
AppboyLogger.i("AMIRA", String.format("Amira %s", intent.toString()));
String action = intent.getAction();
AppboyLogger.i("AMIRA", String.format("Amira %s", action));
Bundle bundle = intent.getExtras();
for (String key : bundle.keySet()) {
Object value = bundle.get(key);
AppboyLogger.i("AMIRA", String.format("Amira %s", key + ":" + value.toString()));
}
}
The root of the problem is that we differentiate deep links and http links based on schema of the URI, so http (and some other schemes) links are detected as web links, and other formats are seen as deep links (see https://github.com/Appboy/appboy-android-sdk/blob/master/android-sdk-ui/src/com/appboy/ui/actions/ActionFactory.java).
We’ll consider how to instrument things for the use case you have, but in the meantime there’s a couple of ways you could solve the issue:
1) Create a deep link that is not also an http link. Everything should work if your link instead looks like, for example, forsale://mylink?a=b&2=3....etc.
2) Set a custom in-app message manager listener: https://documentation.appboy.com/Android/#in-app-message-customization. You can see an example of how we do this in our Droidboy sample app. In your case, you’d want to return defaults for everything but onInAppMessageButtonClicked and onInAppMessageClicked where you’d want to handle the link yourself if it’s of the format of your deep link. Your ticket indicates you’ve tried this, but I’d suggest starting with "the default one we create in the AppboyInAppMessageManager.java (#L608) in the Android SDK - and then just modifying the *clicked methods.
3) Download our UI code and modify the source. You could optionally download the Appboy Android SDK and modify the ActionFactory to handle your deep link in the way you want. Though, at the point you are going to do something like this, solution #2 is likely going to be a nicer one to implement and maintain.
Please let us know if one of these solutions works for you and if you have any other comments/questions.
Thanks,
Waciuma
First of all, I have researched a lot about my issue, but I could not find a proper solution so I am posting my query here. Hope to get a better solution to the issue:
I have a requirement where I need to ask for password to the user before user deletes my app from settings or from any other application like MyAppSharer. I have found one solution where I can successfully be able to call my activity when user clicks on Uninstall button. I have applied trick here, and calling service. In service, I run timer which runs every 1 second and in that one second, it checks for top most activity of running task. This is running perfectly as per expected.
Now, my issue is, this activity apppears on each of application user tries to uninstall. I need that the activity which I call, should only appear for my application when user tries to uninstall my application.
Here is my code:
public static final String PACKAGE_INSTALLER = "com.android.packageinstaller";
public static final String PACKAGE_INSTALLER_UNINSTALL_ACTIVITY = "com.android.packageinstaller.UninstallerActivity";
alarmTimer.scheduleAtFixedRate(new TimerTask() {
public void run() {
mActivityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);;
ComponentName topActivity = mActivityManager.getRunningTasks(1).get(0).topActivity;
final String packageName = topActivity.getPackageName();
String className = topActivity.getClassName();
Log.v(TAG, "packageName:" + packageName);
Log.v(TAG, "className:" + className);
if (PACKAGE_INSTALLER.equals(packageName)
&& PACKAGE_INSTALLER_UNINSTALL_ACTIVITY.equals(className)) {
//Here I need to apply one condition where package name received to be matched with my package name. But I am not sure how to fetch package name of selected application for uninstalling
//To Cancel Existing UninstallerActivity and redirect user to home.
Intent homeIntent = new Intent();
homeIntent.setAction(Intent.ACTION_MAIN);
homeIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
homeIntent.addCategory(Intent.CATEGORY_HOME);
startActivity(homeIntent);
//To open my activity
Intent loginActivity = new Intent(UninstallService.this, Act_Login.class);
loginActivity.putExtra(Constants.KEY_IS_FROM_SERVICE, true);
loginActivity.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(loginActivity);
}
}
}, 0, 1000);
you should try something like the following :
1st - declare your broadcast recevier in the Manifest file , that will listen to QUERY_PACKAGE_RESTART :
<receiver android:name=".UninstallReceiver">
<intent-filter android:priority="999999">
<action android:name="android.intent.action.QUERY_PACKAGE_RESTART" />
<data android:scheme="package" />
</intent-filter>
</receiver>
2nd - your UnunstallIntentReceiver java class like the following :
public class UninstallReceiver extends BroadcastReceiver{
#Override
public void onReceive(Context context, Intent intent) {
// fetching package names from extras
String[] packageNames = intent.getStringArrayExtra("android.intent.extra.PACKAGES");
if(packageNames!=null){
for(String packageName: packageNames){
if(packageName!=null && packageName.equals("application_package")){
// start your activity here and ask the user for the password
}
}
}
}
}
and please give me some feedback
Hope That Helps.
If this is a corporate requirement (if you want to block a regular user from uninstalling your app, no chance, thanks Google for protecting us from bad devs), you should create a device administrator application. This way, although the user still can delete the app, it's one extra step if you want to prevent accidental erasing.
Before deleting your app, if it's enabled as device admin, the user must first disable the app as administrator, and the app receives this broadcast.
In your XML, put
<activity android:name=".app.DeviceAdminSample"
android:label="#string/activity_sample_device_admin">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.SAMPLE_CODE" />
</intent-filter>
</activity>
<receiver android:name=".app.DeviceAdminSample$DeviceAdminSampleReceiver"
android:label="#string/sample_device_admin"
android:description="#string/sample_device_admin_description"
android:permission="android.permission.BIND_DEVICE_ADMIN">
<meta-data android:name="android.app.device_admin"
android:resource="#xml/device_admin_sample" />
<intent-filter>
<action android:name="android.app.action.DEVICE_ADMIN_ENABLED" />
</intent-filter>
</receiver>
In the receiver, you have at least two methods worth noticing:
#Override
public CharSequence onDisableRequested(Context context, Intent intent) {
…
}
#Override
public void onDisabled(Context context, Intent intent) {
…
}
This way you know the user is potentially going to erase your app.
Complete guide for device administration is at https://developer.android.com/guide/topics/admin/device-admin.html
If you have root permissions make your app system (remove your apk-file from /data to /system directories). Then reboot device. After reboot your app is not available to delete by user (not superuser).
The only way i see, is to provide your own uninstaller as part of your app (= an activity that lists all apps and allows to uninstall them). Your service could then check if your app was the one that started the packageinstaller and if not redirect the user.
It is not possible (at least on the Android 4.4 I tested with) to grab the uninstaller activity data without root or being a system app. This is because the uninstaller is not called as an independent task, but as an activity on the stack of the starting task (which is the Settings app when uninstalling from settings, etc). You can only see the Task details of the calling task.
However there might be some really dirty possibility left, that i didn't test to the end: You could register the hidden interface IThumbnailReceiver [1] with the hidden three argument version of ActivityManager.getRunningTasks [2]. It seems like only the GET_TASKS permission is needed to grab a thumbnail (see [3]). It should be possible to find out which app is going to be removed from the app thumbnail... - But as this solution uses hidden APIs, there is no guarantee that it will work with older/newer/vendored Android versions.
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/core/java/android/app/IThumbnailReceiver.aidl
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/core/java/android/app/ActivityManager.java#L766
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/services/java/com/android/server/am/ActivityManagerService.java#L6725
First of all, I have researched a lot about my issue, but I could not find a proper solution so I am posting my query here. Hope to get a better solution to the issue:
I have a requirement where I need to ask for password to the user before user deletes my app from settings or from any other application like MyAppSharer. I have found one solution where I can successfully be able to call my activity when user clicks on Uninstall button. I have applied trick here, and calling service. In service, I run timer which runs every 1 second and in that one second, it checks for top most activity of running task. This is running perfectly as per expected.
Now, my issue is, this activity apppears on each of application user tries to uninstall. I need that the activity which I call, should only appear for my application when user tries to uninstall my application.
Here is my code:
public static final String PACKAGE_INSTALLER = "com.android.packageinstaller";
public static final String PACKAGE_INSTALLER_UNINSTALL_ACTIVITY = "com.android.packageinstaller.UninstallerActivity";
alarmTimer.scheduleAtFixedRate(new TimerTask() {
public void run() {
mActivityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);;
ComponentName topActivity = mActivityManager.getRunningTasks(1).get(0).topActivity;
final String packageName = topActivity.getPackageName();
String className = topActivity.getClassName();
Log.v(TAG, "packageName:" + packageName);
Log.v(TAG, "className:" + className);
if (PACKAGE_INSTALLER.equals(packageName)
&& PACKAGE_INSTALLER_UNINSTALL_ACTIVITY.equals(className)) {
//Here I need to apply one condition where package name received to be matched with my package name. But I am not sure how to fetch package name of selected application for uninstalling
//To Cancel Existing UninstallerActivity and redirect user to home.
Intent homeIntent = new Intent();
homeIntent.setAction(Intent.ACTION_MAIN);
homeIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
homeIntent.addCategory(Intent.CATEGORY_HOME);
startActivity(homeIntent);
//To open my activity
Intent loginActivity = new Intent(UninstallService.this, Act_Login.class);
loginActivity.putExtra(Constants.KEY_IS_FROM_SERVICE, true);
loginActivity.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(loginActivity);
}
}
}, 0, 1000);
you should try something like the following :
1st - declare your broadcast recevier in the Manifest file , that will listen to QUERY_PACKAGE_RESTART :
<receiver android:name=".UninstallReceiver">
<intent-filter android:priority="999999">
<action android:name="android.intent.action.QUERY_PACKAGE_RESTART" />
<data android:scheme="package" />
</intent-filter>
</receiver>
2nd - your UnunstallIntentReceiver java class like the following :
public class UninstallReceiver extends BroadcastReceiver{
#Override
public void onReceive(Context context, Intent intent) {
// fetching package names from extras
String[] packageNames = intent.getStringArrayExtra("android.intent.extra.PACKAGES");
if(packageNames!=null){
for(String packageName: packageNames){
if(packageName!=null && packageName.equals("application_package")){
// start your activity here and ask the user for the password
}
}
}
}
}
and please give me some feedback
Hope That Helps.
If this is a corporate requirement (if you want to block a regular user from uninstalling your app, no chance, thanks Google for protecting us from bad devs), you should create a device administrator application. This way, although the user still can delete the app, it's one extra step if you want to prevent accidental erasing.
Before deleting your app, if it's enabled as device admin, the user must first disable the app as administrator, and the app receives this broadcast.
In your XML, put
<activity android:name=".app.DeviceAdminSample"
android:label="#string/activity_sample_device_admin">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.SAMPLE_CODE" />
</intent-filter>
</activity>
<receiver android:name=".app.DeviceAdminSample$DeviceAdminSampleReceiver"
android:label="#string/sample_device_admin"
android:description="#string/sample_device_admin_description"
android:permission="android.permission.BIND_DEVICE_ADMIN">
<meta-data android:name="android.app.device_admin"
android:resource="#xml/device_admin_sample" />
<intent-filter>
<action android:name="android.app.action.DEVICE_ADMIN_ENABLED" />
</intent-filter>
</receiver>
In the receiver, you have at least two methods worth noticing:
#Override
public CharSequence onDisableRequested(Context context, Intent intent) {
…
}
#Override
public void onDisabled(Context context, Intent intent) {
…
}
This way you know the user is potentially going to erase your app.
Complete guide for device administration is at https://developer.android.com/guide/topics/admin/device-admin.html
If you have root permissions make your app system (remove your apk-file from /data to /system directories). Then reboot device. After reboot your app is not available to delete by user (not superuser).
The only way i see, is to provide your own uninstaller as part of your app (= an activity that lists all apps and allows to uninstall them). Your service could then check if your app was the one that started the packageinstaller and if not redirect the user.
It is not possible (at least on the Android 4.4 I tested with) to grab the uninstaller activity data without root or being a system app. This is because the uninstaller is not called as an independent task, but as an activity on the stack of the starting task (which is the Settings app when uninstalling from settings, etc). You can only see the Task details of the calling task.
However there might be some really dirty possibility left, that i didn't test to the end: You could register the hidden interface IThumbnailReceiver [1] with the hidden three argument version of ActivityManager.getRunningTasks [2]. It seems like only the GET_TASKS permission is needed to grab a thumbnail (see [3]). It should be possible to find out which app is going to be removed from the app thumbnail... - But as this solution uses hidden APIs, there is no guarantee that it will work with older/newer/vendored Android versions.
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/core/java/android/app/IThumbnailReceiver.aidl
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/core/java/android/app/ActivityManager.java#L766
https://github.com/omnirom/android_frameworks_base/blob/android-4.4/services/java/com/android/server/am/ActivityManagerService.java#L6725