Android: Add possibility to listen for changes in app states

This is useful for example the embedded QML case, where we want to
make sure everything from Qt side is ready before we start to create
Qt windows.

Pick-to: 6.7
Change-Id: I8148405e35cc8ebb89110f05e07cef06f8ff3709
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/android/jar/src/org/qtproject/qt/android/QtNative.java

@@ -47,6 +47,8 @@ class QtNative
     private static ClassLoader m_classLoader = null;
 
     private static final Runnable runPendingCppRunnablesRunnable = QtNative::runPendingCppRunnables;
+    private static final ArrayList<AppStateDetailsListener> m_appStateListeners = new ArrayList<>();
+    private static final Object m_appStateListenersLock = new Object();
 
     @UsedFromNativeCode
     public static ClassLoader classLoader()
@@ -193,6 +195,10 @@ class QtNative
         return m_qtThread;
     }
 
+    interface AppStateDetailsListener {
+        void onAppStateDetailsChanged(ApplicationStateDetails details);
+    }
+
     // Keep in sync with src/corelib/global/qnamespace.h
     public static class ApplicationState {
         static final int ApplicationSuspended = 0x0;
@@ -215,12 +221,14 @@ class QtNative
     public static void setStarted(boolean started)
     {
         m_stateDetails.isStarted = started;
+        notifyAppStateDetailsChanged(m_stateDetails);
     }
 
     @UsedFromNativeCode
     public static void notifyNativePluginIntegrationReady(boolean ready)
     {
         m_stateDetails.nativePluginIntegrationReady = ready;
+        notifyAppStateDetailsChanged(m_stateDetails);
     }
 
     public static void setApplicationState(int state)
@@ -234,6 +242,27 @@ class QtNative
             }
         }
         updateApplicationState(state);
+        notifyAppStateDetailsChanged(m_stateDetails);
+    }
+
+    static void registerAppStateListener(AppStateDetailsListener listener) {
+        synchronized (m_appStateListenersLock) {
+            if (!m_appStateListeners.contains(listener))
+                m_appStateListeners.add(listener);
+        }
+    }
+
+    static void unregisterAppStateListener(AppStateDetailsListener listener) {
+        synchronized (m_appStateListenersLock) {
+            m_appStateListeners.remove(listener);
+        }
+    }
+
+    static void notifyAppStateDetailsChanged(ApplicationStateDetails details) {
+        synchronized (m_appStateListenersLock) {
+            for (AppStateDetailsListener listener : m_appStateListeners)
+                listener.onAppStateDetailsChanged(details);
+        }
     }
 
     // Post a runnable to Main (UI) Thread if the app is active,
@@ -289,6 +318,7 @@ class QtNative
             m_qtThread.post(QtNative::startQtApplication);
             waitForServiceSetup();
             m_stateDetails.isStarted = true;
+            notifyAppStateDetailsChanged(m_stateDetails);
         }
     }
 
@@ -301,6 +331,7 @@ class QtNative
             if (isServiceValid())
                 m_service.get().stopSelf();
             m_stateDetails.isStarted = false;
+            // Likely no use to call notifyAppStateDetailsChanged at this point since we are exiting
         });
     }