Add a preference to use a single instance for loading files

Contributes to #7664

cura/CuraApplication.py

@@ -304,6 +304,7 @@ class CuraApplication(QtApplication):
 
         super().initialize()
 
+        self._checkEarlyPreferences()
         self.__sendCommandToSingleInstance()
         self._initializeSettingDefinitions()
         self._initializeSettingFunctions()
@@ -314,6 +315,20 @@ class CuraApplication(QtApplication):
         self._machine_action_manager = MachineActionManager.MachineActionManager(self)
         self._machine_action_manager.initialize()
 
+    def _checkEarlyPreferences(self) -> None:
+        # Check for specific preferences early in the bootstrap process, without spinning up the full Preference singleton yet
+        if self._use_single_instance:
+            return
+
+        preferences_file = Resources.getPath(Resources.Preferences, "{}.cfg".format(self.getApplicationName()))
+        if not os.path.exists(preferences_file):
+            return
+
+        with open(preferences_file) as preferences:
+            if "single_instance = True" in preferences.read():
+                Logger.log("i", "Preference to use a single instance detected")
+                self._use_single_instance = True
+
     def __sendCommandToSingleInstance(self):
         self._single_instance = SingleInstance(self, self._files_to_open)
 
@@ -508,7 +523,7 @@ class CuraApplication(QtApplication):
         preferences.setValue("metadata/setting_version", self.SettingVersion) #Don't make it equal to the default so that the setting version always gets written to the file.
 
         preferences.addPreference("cura/active_mode", "simple")
-
+        preferences.addPreference("cura/single_instance", False)
         preferences.addPreference("cura/categories_expanded", "")
         preferences.addPreference("cura/jobname_prefix", True)
         preferences.addPreference("cura/select_models_on_load", False)

resources/qml/Preferences/GeneralPage.qml

@@ -72,6 +72,9 @@ UM.PreferencesPage
         var defaultTheme = UM.Preferences.getValue("general/theme")
         setDefaultTheme(defaultTheme)
 
+        UM.Preferences.resetPreference("cura/single_instance")
+        scaleToFitCheckbox.checked = boolCheck(UM.Preferences.getValue("cura/single_instance"))
+
         UM.Preferences.resetPreference("physics/automatic_push_free")
         pushFreeCheckbox.checked = boolCheck(UM.Preferences.getValue("physics/automatic_push_free"))
         UM.Preferences.resetPreference("physics/automatic_drop_down")
@@ -560,6 +563,21 @@ UM.PreferencesPage
                 text: catalog.i18nc("@label","Opening and saving files")
             }
 
+            UM.TooltipArea
+            {
+                width: childrenRect.width
+                height: childrenRect.height
+                text: catalog.i18nc("@info:tooltip","Should opening files from the desktop or external applications open in the same instance of Cura?")
+
+                CheckBox
+                {
+                    id: singleInstanceCheckbox
+                    text: catalog.i18nc("@option:check","Use a single instance of Cura")
+                    checked: boolCheck(UM.Preferences.getValue("cura/single_instance"))
+                    onCheckedChanged: UM.Preferences.setValue("cura/single_instance", checked)
+                }
+            }
+
             UM.TooltipArea
             {
                 width: childrenRect.width