add missing file

Author: maartenbreddels

glue_jupyter/common/hooks.py

@@ -0,0 +1,43 @@
+from glue.viewers.common.viewer import Viewer
+from glue.viewers.common.state import State
+import react_ipywidgets as react
+
+def use_echo_state(state: State, name):
+    value, set_value = react.use_state(getattr(state, name), key=name)
+
+    def add_event_handler():
+        def handler(new_value):
+            set_value(new_value)
+
+        def cleanup():
+            state.remove_callback(name, handler)
+
+        state.add_callback(name, handler)
+        return cleanup
+
+    react.use_side_effect(add_event_handler)
+
+    def set_value_sync(new_value):
+        setattr(
+            state, name, new_value
+        )  # this will update us via add_event_handler, no need to call set_value
+
+    return value, set_value_sync
+
+
+def use_layer_watch(viewer: Viewer):
+    # use a counter to force updates due to external state changes
+    counter, set_counter = react.use_state(0)
+
+    def hookup():
+        def handler():
+            new_counter = counter + 1
+            set_counter(new_counter)
+
+        def cleanup():
+            viewer._layer_artist_container.change_callbacks.remove(handler)
+
+        viewer._layer_artist_container.on_changed(handler)
+        return cleanup
+
+    react.use_side_effect(hookup)