add keep-alive to ui.stepper (fixes #1638)

nicegui/elements/stepper.py

@@ -13,16 +13,23 @@ class Stepper(ValueElement):
     def __init__(self, *,
                  value: Union[str, Step, None] = None,
                  on_value_change: Optional[Callable[..., Any]] = None,
+                 keep_alive: bool = True,
                  ) -> None:
         """Stepper
 
         This element represents `Quasar's QStepper <https://quasar.dev/vue-components/stepper#qstepper-api>`_ component.
         It contains individual steps.
 
+        To avoid issues with dynamic elements when switching steps,
+        this element uses Vue's `keep-alive <https://vuejs.org/guide/built-ins/keep-alive.html>`_ component.
+        If client-side performance is an issue, you can disable this feature.
+
         :param value: `ui.step` or name of the step to be initially selected (default: `None` meaning the first step)
         :param on_value_change: callback to be executed when the selected step changes
+        :param keep_alive: whether to use Vue's keep-alive component on the content (default: `True`)
         """
         super().__init__(tag='q-stepper', value=value, on_value_change=on_value_change)
+        self._props['keep-alive'] = keep_alive
 
     def _value_to_model_value(self, value: Any) -> Any:
         return value._props['name'] if isinstance(value, Step) else value  # pylint: disable=protected-access