Merge pull request #14 from ssciwr/observer-fixes

Observer fixes

ipywidgets_jsonschema/__init__.py

@@ -1,3 +1,3 @@
 from ipywidgets_jsonschema.form import Form
 
-__version__ = "0.3.0"
+__version__ = "0.3.1"

ipywidgets_jsonschema/form.py

@@ -19,6 +19,13 @@ class FormError(Exception):
 )
 
 
+def as_tuple(obj):
+    if isinstance(obj, collections.abc.Iterable) and not isinstance(obj, str):
+        return obj
+    else:
+        return (obj,)
+
+
 class Form:
     def __init__(self, schema, vertically_place_labels=False, use_sliders=False):
         """Create a form with Jupyter widgets from a JSON schema
@@ -51,6 +58,9 @@ def __init__(self, schema, vertically_place_labels=False, use_sliders=False):
         self.vertically_place_labels = vertically_place_labels
         self.use_sliders = use_sliders
 
+        # Store a list of registered observers to add them to runtime-generated widgets
+        self._observers = []
+
         # Construct the widgets
         self._form_element = self._construct(schema, root=True, label=None)
 
@@ -72,6 +82,7 @@ def construct_element(
 
     def observe(self, handler, names=traitlets.All, type="change"):
         """Register a change handler with all the widgets that support it"""
+        self._observers.append((handler, names, type))
         self._form_element.register_observer(handler, names, type)
 
     @property
@@ -331,8 +342,15 @@ def add_entry(_):
                 if len(vbox.children) == schema["maxItems"] + 1:
                     return
 
-            elements.insert(0, self._construct(schema["items"], label=None))
+            newelem = self._construct(schema["items"], label=None)
+            elements.insert(0, newelem)
             item = elements[0].widgets[0]
+
+            # Register existing observers
+            for h, n, t in self._observers:
+                newelem.register_observer(h, n, t)
+
+            # Add array controls to our new element
             trash = ipywidgets.Button(
                 icon="trash", layout=ipywidgets.Layout(width="33%")
             )
@@ -343,6 +361,25 @@ def add_entry(_):
                 icon="arrow-down", layout=ipywidgets.Layout(width="33%")
             )
 
+            def trigger_observers():
+                # Adding or removing an entry to this widget should trigger all value change handlers.
+                # As we do not have a proper widget to register the handler, we trigger it
+                # ourselves. This should make proper use of traitlets.
+                for h, n, t in self._observers:
+                    if t == "change" and (n is traitlets.All or "value" in as_tuple(n)):
+                        h(
+                            {
+                                "name": "value",
+                                "old": {},
+                                "new": {},
+                                "owner": None,
+                                "type": "change",
+                            }
+                        )
+
+            # We trigger observers upon adding
+            trigger_observers()
+
             def remove_entry(b):
                 # If we are at the specified minimum, remove should be ignored
                 if "minItems" in schema:
@@ -358,6 +395,9 @@ def remove_entry(b):
                 vbox.children = vbox.children[:index] + vbox.children[index + 1 :]
                 elements.pop(index)
 
+                # We trigger observers upon removing
+                trigger_observers()
+
             trash.on_click(remove_entry)
 
             def move(dir):
@@ -455,7 +495,7 @@ def _construct_anyof(self, schema, label=None, key="anyOf"):
         widget = ipywidgets.VBox([selector] + elements[0].widgets)
 
         # Whenever there is a change, we switch the subschema widget
-        def _select(change):
+        def _select(_):
             widget.children = [selector] + elements[names.index(selector.value)].widgets
 
         selector.observe(_select)