feat: add use_trait_observe and use_dark_effective

Makes it easy to observe traits, and the example application of this
is use_dark_effective.

solara/hooks/misc.py

@@ -27,6 +27,7 @@
     "use_unique_key",
     "use_state_or_update",
     "use_previous",
+    "use_trait_observe",
 ]
 T = TypeVar("T")
 U = TypeVar("U")
@@ -232,3 +233,31 @@ def assign():
 
     solara.use_effect(assign, [value])
     return ref.current
+
+
+def use_trait_observe(has_trait_object, name):
+    """Observe a trait on an object, and return its value.
+
+    This is useful when you want your component to be in sync with a trait
+    of a widget or [HasTraits object](https://traitlets.readthedocs.io/en/stable/).
+
+    When the trait changes, your component will be re-rendered.
+
+    See [use_dark_effective](/api/use_dark_effective) for an example.
+    """
+    counter = solara.use_reactive(0)
+    counter.get()  # make the main component depend on this counter
+
+    def connect():
+        def update(change):
+            counter.value += 1
+
+        has_trait_object.observe(update, name)
+
+        def cleanup():
+            has_trait_object.unobserve(update, name)
+
+        return cleanup
+
+    solara.use_effect(connect, [has_trait_object, name])
+    return getattr(has_trait_object, name)

solara/lab/components/__init__.py

@@ -3,4 +3,4 @@
 from .input_date import InputDate, InputDateRange  # noqa: F401
 from .menu import ClickMenu, ContextMenu, Menu  # noqa: F401 F403
 from .tabs import Tab, Tabs  # noqa: F401
-from .theming import ThemeToggle, theme  # noqa: F401
+from .theming import ThemeToggle, theme, use_dark_effective  # noqa: F401

solara/lab/components/theming.py

@@ -11,6 +11,21 @@
 ipyvuetify.Themes.theme = cast(ipyvuetify.Themes.Theme, theme)
 
 
+def use_dark_effective():
+    """Return True if the frontend is using a dark theme.
+
+    Equivalent of
+
+    ```python
+    solara.use_trait_observe(solara.lab.theme, "dark_effective")
+    ```
+
+    See [use_trait_observe](/api/use_trait_observe).
+
+    """
+    return solara.use_trait_observe(solara.lab.theme, "dark_effective")
+
+
 def _set_theme(themes: Union[Dict[str, Dict[str, str]], None]):
     if themes is None:
         return

solara/website/components/header.py

@@ -5,9 +5,6 @@
 from solara.alias import rv
 from solara.server import settings
 
-# TODO: remove import once function is included in solara
-from solara.website.pages.apps.scatter import use_dark_effective
-
 
 @solara._component_vue("algolia.vue")
 def Algolia(app_id: str, index_name: str, api_key: str, debug=False):
@@ -22,6 +19,7 @@ def Header(
     # use routes of parent (assuming we are a child of a layout)
     route_current, all_routes = solara.use_route(level=-1)
     router = solara.use_router()
+    dark_effective = solara.lab.use_dark_effective()
 
     # set states for menu
     with solara.Column(gap="0px"):
@@ -36,7 +34,7 @@ def Header(
                     with solara.Button(icon=True, class_="hidden-md-and-up", on_click=lambda: on_toggle_left_menu and on_toggle_left_menu()):
                         rv.Icon(children=["mdi-menu"])
                 with solara.Link(path_or_route="/"):
-                    solara.Image(router.root_path + f"/static/assets/images/logo{'_white' if use_dark_effective() else ''}.svg")
+                    solara.Image(router.root_path + f"/static/assets/images/logo{'_white' if dark_effective else ''}.svg")
             rv.Spacer()
 
             if settings.search.enabled:

solara/website/pages/api/__init__.py

@@ -80,6 +80,7 @@
             "use_reactive",
             "use_state",
             "use_state_or_update",
+            "use_trait_observe",
         ],
     },
     {
@@ -136,6 +137,7 @@
             "task",
             "theming",
             "use_task",
+            "use_dark_effective",
         ],
     },
 ]

solara/website/pages/api/use_dark_effective.py

@@ -0,0 +1,13 @@
+"""# use_dark_effective
+
+"""
+import solara
+import solara.autorouting
+import solara.lab
+from solara.website.utils import apidoc
+
+from . import NoPage
+
+title = "use_dark_effective"
+Page = NoPage
+__doc__ += apidoc(solara.lab.use_dark_effective)  # type: ignore

solara/website/pages/api/use_trait_observe.py

@@ -0,0 +1,13 @@
+"""# use_trait_observe
+
+"""
+import solara
+import solara.autorouting
+import solara.lab
+from solara.website.utils import apidoc
+
+from . import NoPage
+
+title = "use_trait_observe"
+Page = NoPage
+__doc__ += apidoc(solara.use_trait_observe)  # type: ignore

solara/website/pages/apps/scatter.py

@@ -49,34 +49,10 @@ def reset():
         State.df.value = None
 
 
-def use_trait_observe(has_trait_object, name):
-    # TODO: this hook should go into solara
-    counter = solara.use_reactive(0)
-    counter.get()  # make the main component depend on this counter
-
-    def connect():
-        def update(change):
-            counter.value += 1
-
-        has_trait_object.observe(update, name)
-
-        def cleanup():
-            has_trait_object.unobserve(update, name)
-
-        return cleanup
-
-    solara.use_effect(connect, [])
-    return getattr(has_trait_object, name)
-
-
-def use_dark_effective():
-    return use_trait_observe(solara.lab.theme, "dark_effective")
-
-
 @solara.component
 def Page():
     df = State.df.value
-    dark_effective = use_dark_effective()
+    dark_effective = solara.lab.use_dark_effective()
 
     # the .scatter will set this cross filter
     filter, _set_filter = solara.use_cross_filter(id(df))
@@ -142,5 +118,5 @@ def get_data():
 @solara.component
 def Layout(children):
     route, routes = solara.use_route()
-    dark_effective = use_dark_effective()
+    dark_effective = solara.lab.use_dark_effective()
     return solara.AppLayout(children=children, toolbar_dark=dark_effective, color=None)  # if dark_effective else "primary")