further improved exception handling and some cleanup

lib/configuration.dart

@@ -58,8 +58,8 @@ class _MyHomePageState extends State<Configuration> {
 
     try{
       token = await connector.getAuthToken(configuration.loginInformation.mail, configuration.loginInformation.password);
-      configuration.devices = await futureDevices; //already fetched just use the data.
-      configuration.eventTypes = await futureEventTypes; //already fetched just use the data.
+      configuration.devices = await connector.fetchCollectionDevices(configuration.currentCollection.id); //await futureDevices; //already fetched just use the data.
+      configuration.eventTypes = await connector.fetchEventTypes();
 
       event.currentEvent.id = 0;
       event.currentEvent.urnId = configuration.devices[0].id; //TODO: fix if devices are an empty list.
@@ -68,7 +68,6 @@ class _MyHomePageState extends State<Configuration> {
       event.currentEvent.label = '';
       event.currentEvent.type = configuration.eventTypes[0].name;
 
-
       var date = DateTime.now().toUtc();
       var isoDate = date.toIso8601String();
       event.currentEvent.startDate = isoDate;
@@ -94,20 +93,13 @@ class _MyHomePageState extends State<Configuration> {
   }
 
   Future<void> fetchInitData() async {
-
     try {
-      //Start fetching all possible sensor data as soon as possible:
       futureCollections = connector.fetchCollections();
-      futureEventTypes = connector.fetchEventTypes();
-      if (configuration.currentCollection.id != -1) {
-        futureDevices = connector.fetchCollectionDevices(configuration.currentCollection.id);
-      }
-
-      await futureCollections;
-      await futureEventTypes;
-      await futureDevices;
+      await futureCollections;  //wait and catch error here!
     }catch(e){
       debugPrint(e.toString());
+      _status = '$e';
+      setState(() {});
     }
   }
 
@@ -116,7 +108,6 @@ class _MyHomePageState extends State<Configuration> {
     super.initState();
     fetchInitData();
   }
-  late Future<String> eventTypes;
 
   @override
   Widget build(BuildContext context) {
@@ -153,9 +144,6 @@ class _MyHomePageState extends State<Configuration> {
                     onChanged: (value) {
                       configuration.loginInformation.mail = value;
                     },
-                    onFieldSubmitted: (value) {
-                      //futureAuthToken = connector.getAuthToken(configuration.loginInformation.mail, configuration.loginInformation.password);
-                    },
                   ),
                   const SizedBox(height: 15.0),
                   TextFormField(
@@ -170,9 +158,6 @@ class _MyHomePageState extends State<Configuration> {
                     onChanged: (value){
                       configuration.loginInformation.password = value;
                     },
-                    onFieldSubmitted: (value) {
-                      //futureAuthToken = connector.getAuthToken(configuration.loginInformation.mail, configuration.loginInformation.password);
-                    },
                   ),
                   const SizedBox(height: 50),
                   FutureBuilder<List<Collection>>(
@@ -185,12 +170,9 @@ class _MyHomePageState extends State<Configuration> {
                             configuration.collections.add(element);
                           });
 
-                          /*Initialize active collection with first received
-                    collection if not initialized yet*/
+                          /*Initialize active collection with first received collection if not initialized yet*/
                           if(configuration.currentCollection.id == -1){
                             configuration.currentCollection = configuration.collections[0];
-                            futureDevices = connector.fetchCollectionDevices(configuration.currentCollection.id);
-                            //TODO: shall this be removed here and just done at confirmation.?
                           }
 
                           return DropdownButtonFormField(
@@ -213,6 +195,10 @@ class _MyHomePageState extends State<Configuration> {
                               }
                           );
                         }
+                        if (snapshot.hasError) {
+                         debugPrint('Some error happened');
+                         return const CircularProgressIndicator();
+                        }
                         else{
                           return const CircularProgressIndicator();
                         }