disposing popups when leaving widget.

lib/configuration.dart

@@ -20,9 +20,15 @@ class _MyHomePageState extends State<Configuration> {
   late Future<List<EventType>> futureEventTypes;
   late Future<List<Device>> futureDevices;
   late Future<String> futureAuthToken;
+
+
   var database = DatabaseInstance();
   SensorConnector connector = SensorConnector();
   final ConfigurationStoreInstance configuration = ConfigurationStoreInstance();
+
+  late OverlayEntry _overlayEntry;
+
+  bool _initError = false;
   String _status = '';
   TextStyle _statusStyle = const TextStyle(color: Colors.black);
 
@@ -49,21 +55,39 @@ class _MyHomePageState extends State<Configuration> {
       await file.writeAsString(eventsJson);
       debugPrint('Stored file at: ' + filepath);
 
-      _status = 'Event database dump created: ' + filepath;
-      _statusStyle = const TextStyle(color: Colors.green);
       setState(() {});
       HapticFeedback.vibrate();
-      _showResultPopup(context, _status);
+      _showResultPopup(context, 'Event database dump created: ' + filepath,
+          false
+      );
     }
   }
 
 
-  void _showResultPopup(BuildContext context, String text) async {
+
+  Future<void> _showResultPopup(BuildContext context, String text, bool error) async {
     // Declaring and Initializing OverlayState
     // and OverlayEntry objects
     OverlayState? overlayState = Overlay.of(context);
-    OverlayEntry overlayEntry;
-    overlayEntry = OverlayEntry(builder: (context) {
+    try {
+      _overlayEntry.remove();  // Allow only one Overlay Popup
+    }catch(e){
+      debugPrint('Overlay already removed, during dispose: ' + e.toString());
+    }
+    _overlayEntry = OverlayEntry(builder: (context) {    //:
+
+      Color backGroundColor;
+      Color textColor;
+      if (error == true){
+        //This is a error message display red!
+        backGroundColor = Colors.redAccent;
+        textColor = Colors.black;
+      }
+      else {
+        //This is a normal message display green!
+        backGroundColor = Colors.greenAccent;
+        textColor = Colors.black;
+      }
 
       // You can return any widget you like
       // here to be displayed on the Overlay
@@ -75,7 +99,7 @@ class _MyHomePageState extends State<Configuration> {
             bottom: MediaQuery.of(context).size.height * 0.1,
             child: Material(
               borderRadius: BorderRadius.circular(8.0),
-              color: Colors.blue,
+              color: backGroundColor, //Some transparency remains
               child:  Container(
                 padding: const EdgeInsets.all(5.0), // Space between Text and Bubble
                 width: MediaQuery.of(context).size.width * 0.95,
@@ -85,9 +109,9 @@ class _MyHomePageState extends State<Configuration> {
                   readOnly: true,
                   autofocus: false,
                   enabled: false,
-                  //style: _statusStyle,
+                  style: TextStyle(color: textColor),
                   controller: TextEditingController(
-                    text: _status,
+                    text: text,
                   ),
                 ),
               ),
@@ -98,16 +122,20 @@ class _MyHomePageState extends State<Configuration> {
     });
 
     // Inserting the OverlayEntry into the Overlay
-    overlayState?.insert(overlayEntry);
+    overlayState?.insert(_overlayEntry);
 
     // Awaiting for 5 seconds
     await Future.delayed(const Duration(seconds: 5));
 
     // Removing the OverlayEntry from the Overlay
-    overlayEntry.remove();
+    try {
+      _overlayEntry.remove();  //NOTE: Is this a quick an dirty or a proper solution?
+    }catch(e){
+      debugPrint('Overlay already removed, during dispose: ' + e.toString());
+    }
   }
 
-  Future<void> updateConfiguration() async {
+  Future<void> updateConfiguration(BuildContext context) async {
     final EventStoreInstance event = EventStoreInstance();
     String token = '';
 
@@ -133,22 +161,25 @@ class _MyHomePageState extends State<Configuration> {
       configuration.initialized = true;
 
       HapticFeedback.vibrate();
-      //TODO: display success user feedback
-      //TODO: store complete "configuration"
-
       await event.storeToSharedPrefs();
       await configuration.storeToSharedPrefs();
       debugPrint('Configuration stored!');
 
-      _status = 'Login success, got all EventTypes, loaded Collection Devices & stored configuration for offline usage.';
-      _statusStyle = const TextStyle(color: Colors.green);
+      _showResultPopup(context,
+          'Login success, got all EventTypes, loaded Collection Devices & stored configuration for offline usage.',
+          false
+      );
       setState(() {});
 
     } catch (e) {
       String errorText = e.toString();
       errorText = errorText.substring(10, errorText.length);  //Remove 'Exception' from string.
-      _status = errorText;
-      _statusStyle = const TextStyle(color: Colors.red);
+
+      _showResultPopup(context,
+          errorText,
+          true
+      );
+
       setState(() {});
     }
   }
@@ -157,11 +188,14 @@ class _MyHomePageState extends State<Configuration> {
     try {
       futureCollections = connector.fetchCollections();
       await futureCollections;  //wait and catch error here!
+      setState(() {});
+
     }catch(e){
       String errorText = e.toString();
-      errorText = errorText.substring(10, errorText.length);  //Remove 'Exception' from string.
-      _status = errorText;
-      _statusStyle = const TextStyle(color: Colors.red);
+      errorText = errorText.substring(10, errorText.length);
+
+      _status = errorText;  //store errorText globally for pop up message during Widget build
+      _initError = true; //Trigger popup error display!
       setState(() {});
     }
   }
@@ -172,6 +206,16 @@ class _MyHomePageState extends State<Configuration> {
     fetchInitData();
   }
 
+  @override
+  void dispose() {
+    try {
+      _overlayEntry.remove();
+    }catch(e){
+      debugPrint('Dispose error: ' + e.toString());
+    }
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     final ConfigurationStoreInstance configuration = ConfigurationStoreInstance();
@@ -261,6 +305,12 @@ class _MyHomePageState extends State<Configuration> {
                       }
                       if (snapshot.hasError) {
                         debugPrint('Some error happened');
+
+                        if(_initError == true){
+                          _initError = false;
+                          //_showResultPopup(context, _status, true); //TODO: opening a popup does not work properly from here.
+                        }
+
                         return const CircularProgressIndicator();
                       }
                       else{
@@ -285,36 +335,36 @@ class _MyHomePageState extends State<Configuration> {
           ),
         ),
         bottomNavigationBar: Container(
-          margin: const EdgeInsets.symmetric(vertical: 10.0, horizontal: 5.0),
-          child:Row(
-            mainAxisAlignment: MainAxisAlignment.spaceBetween,
-            mainAxisSize: MainAxisSize.max,
-            children: [
-              FloatingActionButton.extended(
-                heroTag: null,
-                tooltip: 'Export events to local .json file',
-                icon: const Icon(Icons.download),
-                label: const Text('Dump Events'),
-                onPressed: () {
-                  dumpToFile(context);
-
-                  //Reset for debug testing only. //Remove in RELEASE Version:
-                  //database.delete();
-                  //events.reset();
-                  //configuration.reset();
-                },
-              ),
-              FloatingActionButton.extended(
-                heroTag: null,
-                tooltip: 'Download corresponding devices and store locally',
-                icon: const Icon(Icons.save),
-                label: const Text('Set'),
-                onPressed: () {
-                  updateConfiguration();
-                },
-              ),
-            ],
-          ),
+            margin: const EdgeInsets.symmetric(vertical: 10.0, horizontal: 5.0),
+            child:Row(
+              mainAxisAlignment: MainAxisAlignment.spaceBetween,
+              mainAxisSize: MainAxisSize.max,
+              children: [
+                FloatingActionButton.extended(
+                  heroTag: null,
+                  tooltip: 'Export events to local .json file',
+                  icon: const Icon(Icons.download),
+                  label: const Text('Dump Events'),
+                  onPressed: () {
+                    dumpToFile(context);
+
+                    //Reset for debug testing only. //Remove in RELEASE Version:
+                    //database.delete();
+                    //events.reset();
+                    //configuration.reset();
+                  },
+                ),
+                FloatingActionButton.extended(
+                  heroTag: null,
+                  tooltip: 'Download corresponding devices and store locally',
+                  icon: const Icon(Icons.save),
+                  label: const Text('Set'),
+                  onPressed: () {
+                    updateConfiguration(context);
+                  },
+                ),
+              ],
+            )
         )
     );
   }