fix: invoking gui interface twice

Author: e3rd

docs/Changelog.md

@@ -2,6 +2,7 @@
 
 ## unreleased
 * enh: config file union support
+* fix: invoking gui interface twice
 
 ## 1.2.1 (2025-10-24)
 * deps (tyro): ready for 0.10

mininterface/_lib/cli_parser.py

@@ -245,15 +245,7 @@ def annot(type_form):
                     kwargs, None if helponly else m, args, type_form, env_classes, _custom_registry, annot, _req_fields
                 )
 
-        # Why setting m.env instead of putting into into a constructor of a new get_interface() call?
-        # 1. Getting the interface is a costly operation
-        # 2. There is this bug so that we need to use single interface:
-        #    TODO
-        #    As this works badly, lets make sure we use single interface now
-        #    and will not need the second one.
-        #    get_interface("gui")
-        #    m = get_interface("gui")
-        #    m.select([1,2,3])
+        # Make the interface ready for the user
         m.env = env
     except SystemExit as exception:
         # --- (C) The dialog missing section ---

mininterface/_tk_interface/adaptor.py

@@ -32,14 +32,35 @@ class TkAdaptor(Tk, RichUiAdaptor, BackendAdaptor):
     facet: TkFacet
     settings: GuiSettings
 
+    _instance = None
+    """ singleton """
+
+    def __new__(cls, *args, **kwargs):
+        # Singleton.
+        # Why enforcing singleton?
+        # Invoking second tk would mean a strange second window
+        # and non-responding tkinter variables in the second invocation.
+        #    get_interface("gui")
+        #    m = get_interface("gui")
+        #    m.select([1,2,3])  # cannot choose the value
+        if cls._instance is None:
+            return Tk.__new__(cls)
+        return cls._instance
+
     def __init__(self, *args):
+        if self._instance:
+            return
+        else:
+            self.__class__._instance = self
+
         BackendAdaptor.__init__(self, *args)
 
         try:
             Tk.__init__(self)
         except TclError:
             # even when installed the libraries are installed, display might not be available, hence tkinter fails
             raise InterfaceNotAvailable
+        self._initialized = True
 
         self.params = None
         self._result = None