WindowChangeDetectingService.java

public class WindowChangeDetectingService extends AccessibilityService {

    @Override
    protected void onServiceConnected() {
        super.onServiceConnected();

        //Configure these here for compatibility with API 13 and below.
        AccessibilityServiceInfo config = new AccessibilityServiceInfo();
        config.eventTypes = AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED;// | AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED;
        config.feedbackType = AccessibilityServiceInfo.FEEDBACK_GENERIC;// |  AccessibilityServiceInfo.FEEDBACK_SPOKEN;

        if (Build.VERSION.SDK_INT >= 16)
            //Just in case this helps
            config.flags = AccessibilityServiceInfo.FLAG_INCLUDE_NOT_IMPORTANT_VIEWS;

        setServiceInfo(config);
    }

    @Override
    public void onAccessibilityEvent(AccessibilityEvent event)
    {
        if (event.getEventType() == AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED)
        {
            String packageName = event.getPackageName() != null ? event.getPackageName().toString() : "";
            String activityName = event.getClassName() != null ? event.getClassName().toString() : "";
            // do something with the information
            // ...
        }
        else if (event.getEventType() == AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED)
        {
            L.d(this, "event: " + event.toString());
        }
    }

    @Override
    public void onInterrupt() {}
}

don't forget to add the service to the manifest:

<service
        android:label="@string/app_name"
        android:name=".services.WindowChangeDetectingService"
        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/accessibilityservice"/>
    </service>

The xml looks something like following:

<?xml version="1.0" encoding="utf-8"?>
<!-- These options MUST be specified here in order for the events to be received on first start in Android 4.1.1 -->
<accessibility-service
xmlns:tools="http://schemas.android.com/tools"
android:accessibilityEventTypes="typeWindowStateChanged"
android:accessibilityFeedbackType="feedbackGeneric"
android:accessibilityFlags="flagIncludeNotImportantViews"
android:description="@string/accessibility_service_description"
xmlns:android="http://schemas.android.com/apk/res/android"
tools:ignore="UnusedAttribute"/>