Fix occasional crash when entering profiles section.

Make QualityManagementModel into a singleton.
part of CURA-6600

cura/CuraApplication.py

@@ -221,8 +221,9 @@ class CuraApplication(QtApplication):
         self._cura_scene_controller = None
         self._machine_error_checker = None
 
-        self._machine_settings_manager = MachineSettingsManager(self, parent = self)
+        self._machine_settings_manager = MachineSettingsManager(self, parent=self)
         self._material_management_model = MaterialManagementModel()
+        self._quality_management_model = None
 
         self._discovered_printer_model = DiscoveredPrintersModel(self, parent = self)
         self._first_start_machine_actions_model = FirstStartMachineActionsModel(self, parent = self)
@@ -981,6 +982,12 @@ class CuraApplication(QtApplication):
     def getMaterialManagementModel(self):
         return self._material_management_model
 
+    @pyqtSlot(result=QObject)
+    def getQualityManagementModel(self):
+        if not self._quality_management_model:
+            self._quality_management_model = QualityManagementModel()
+        return self._quality_management_model
+
     def getSimpleModeSettingsManager(self, *args):
         if self._simple_mode_settings_manager is None:
             self._simple_mode_settings_manager = SimpleModeSettingsManager()
@@ -1059,7 +1066,7 @@ class CuraApplication(QtApplication):
         qmlRegisterType(FavoriteMaterialsModel, "Cura", 1, 0, "FavoriteMaterialsModel")
         qmlRegisterType(GenericMaterialsModel, "Cura", 1, 0, "GenericMaterialsModel")
         qmlRegisterType(MaterialBrandsModel, "Cura", 1, 0, "MaterialBrandsModel")
-        qmlRegisterType(QualityManagementModel, "Cura", 1, 0, "QualityManagementModel")
+        qmlRegisterSingletonType(QualityManagementModel, "Cura", 1, 0, "QualityManagementModel", self.getQualityManagementModel)
         qmlRegisterSingletonType(MaterialManagementModel, "Cura", 1, 5, "MaterialManagementModel", self.getMaterialManagementModel)
 
         qmlRegisterType(DiscoveredPrintersModel, "Cura", 1, 0, "DiscoveredPrintersModel")

resources/qml/Preferences/ProfilesPage.qml

@@ -17,13 +17,10 @@ Item
     property QtObject qualityManager: CuraApplication.getQualityManager()
     property var resetEnabled: false  // Keep PreferencesDialog happy
     property var extrudersModel: CuraApplication.getExtrudersModel()
+    property var qualityManagementModel: CuraApplication.getQualityManagementModel()
 
     UM.I18nCatalog { id: catalog; name: "cura"; }
 
-    Cura.QualityManagementModel {
-        id: qualitiesModel
-    }
-
     Label {
         id: titleLabel
         anchors {
@@ -40,7 +37,7 @@ Item
 
     property var currentItem: {
         var current_index = qualityListView.currentIndex;
-        return (current_index == -1) ? null : qualitiesModel.getItem(current_index);
+        return (current_index == -1) ? null : base.qualityManagementModel.getItem(current_index);
     }
 
     property var currentItemName: hasCurrentItem ? base.currentItem.name : ""
@@ -195,7 +192,7 @@ Item
     // This connection makes sure that we will switch to the correct quality after the model gets updated
     Connections
     {
-        target: qualitiesModel
+        target: base.qualityManagementModel
         onItemsChanged:
         {
             var toSelectItemName = base.currentItem == null ? "" : base.currentItem.name;
@@ -208,9 +205,9 @@ Item
             if (toSelectItemName != "")
             {
                 // Select the required quality name if given
-                for (var idx = 0; idx < qualitiesModel.count; ++idx)
+                for (var idx = 0; idx < base.qualityManagementModel.count; ++idx)
                 {
-                    var item = qualitiesModel.getItem(idx);
+                    var item = base.qualityManagementModel.getItem(idx);
                     if (item.name == toSelectItemName)
                     {
                         // Switch to the newly created profile if needed
@@ -282,7 +279,7 @@ Item
         id: importDialog
         title: catalog.i18nc("@title:window", "Import Profile")
         selectExisting: true
-        nameFilters: qualitiesModel.getFileNameFilters("profile_reader")
+        nameFilters: base.qualityManagementModel.getFileNameFilters("profile_reader")
         folder: CuraApplication.getDefaultPath("dialog_profile_path")
         onAccepted:
         {
@@ -308,7 +305,7 @@ Item
         id: exportDialog
         title: catalog.i18nc("@title:window", "Export Profile")
         selectExisting: false
-        nameFilters: qualitiesModel.getFileNameFilters("profile_writer")
+        nameFilters: base.qualityManagementModel.getFileNameFilters("profile_writer")
         folder: CuraApplication.getDefaultPath("dialog_profile_path")
         onAccepted:
         {
@@ -390,16 +387,16 @@ Item
             {
                 id: qualityListView
 
-                model: qualitiesModel
+                model: base.qualityManagementModel
 
                 Component.onCompleted:
                 {
                     var selectedItemName = Cura.MachineManager.activeQualityOrQualityChangesName;
 
                     // Select the required quality name if given
-                    for (var idx = 0; idx < qualitiesModel.count; idx++)
+                    for (var idx = 0; idx < base.qualityManagementModel.count; idx++)
                     {
-                        var item = qualitiesModel.getItem(idx);
+                        var item = base.qualityManagementModel.getItem(idx);
                         if (item.name == selectedItemName)
                         {
                             currentIndex = idx;