Implement refresh of editors opened from object explorer

* Pass the `data_function` from the object explorer, which can retrieve
  new data for the object being edited, via `ToggleColumnTreeView`
  to `ToggleColumnDelegate`.
* Add `ToggleColumnDelegate.make_data_function()` for retrieving new data
  for editors opened from the object explorer.
* Pass the result of the above function to editors opened from the object
  explorer.
* Add tests for new functionality.

spyder/plugins/variableexplorer/widgets/collectionsdelegate.py

@@ -462,8 +462,11 @@ def updateEditorGeometry(self, editor, option, index):
 
 class ToggleColumnDelegate(CollectionsDelegate):
     """ToggleColumn Item Delegate"""
-    def __init__(self, parent=None, namespacebrowser=None):
-        CollectionsDelegate.__init__(self, parent, namespacebrowser)
+
+    def __init__(self, parent=None, namespacebrowser=None,
+                 data_function: Optional[Callable[[], Any]] = None):
+        CollectionsDelegate.__init__(
+            self, parent, namespacebrowser, data_function)
         self.current_index = None
         self.old_obj = None
 
@@ -483,6 +486,49 @@ def set_value(self, index, value):
         if index.isValid():
             index.model().set_value(index, value)
 
+    def make_data_function(self, index: QModelIndex
+                           ) -> Optional[Callable[[], Any]]:
+        """
+        Construct function which returns current value of data.
+
+        This is used to refresh editors created from this piece of data.
+        For instance, if `self` is the delegate for an editor displays the
+        object `obj` and the user opens another editor for `obj.xxx.yyy`,
+        then to refresh the data of the second editor, the nested function
+        `datafun` first gets the refreshed data for `obj` and then gets the
+        `xxx` attribute and then the `yyy` attribute.
+
+        Parameters
+        ----------
+        index : QModelIndex
+            Index of item whose current value is to be returned by the
+            function constructed here.
+
+        Returns
+        -------
+        Optional[Callable[[], Any]]
+            Function which returns the current value of the data, or None if
+            such a function cannot be constructed.
+        """
+        if self.data_function is None:
+            return None
+
+        obj_path = index.model().get_key(index).obj_path
+        path_elements = obj_path.split('.')
+        del path_elements[0]  # first entry is variable name
+
+        def datafun():
+            data = self.data_function()
+            try:
+                for attribute_name in path_elements:
+                    data = getattr(data, attribute_name)
+                return data
+            except (NotImplementedError, AttributeError,
+                    TypeError, ValueError):
+                return None
+
+        return datafun
+
     def createEditor(self, parent, option, index):
         """Overriding method createEditor"""
         if self.show_warning(index):
@@ -519,7 +565,8 @@ def createEditor(self, parent, option, index):
         if isinstance(value, (list, set, tuple, dict)):
             from spyder.widgets.collectionseditor import CollectionsEditor
             editor = CollectionsEditor(
-                parent=parent, namespacebrowser=self.namespacebrowser)
+                parent=parent, namespacebrowser=self.namespacebrowser,
+                data_function=self.make_data_function(index))
             editor.setup(value, key, icon=self.parent().windowIcon(),
                          readonly=readonly)
             self.create_dialog(editor, dict(model=index.model(), editor=editor,
@@ -528,7 +575,8 @@ def createEditor(self, parent, option, index):
         # ArrayEditor for a Numpy array
         elif (isinstance(value, (np.ndarray, np.ma.MaskedArray)) and
                 np.ndarray is not FakeObject):
-            editor = ArrayEditor(parent=parent)
+            editor = ArrayEditor(
+                parent=parent, data_function=self.make_data_function(index))
             if not editor.setup_and_check(value, title=key, readonly=readonly):
                 return
             self.create_dialog(editor, dict(model=index.model(), editor=editor,
@@ -549,7 +597,8 @@ def createEditor(self, parent, option, index):
         # DataFrameEditor for a pandas dataframe, series or index
         elif (isinstance(value, (pd.DataFrame, pd.Index, pd.Series))
                 and pd.DataFrame is not FakeObject):
-            editor = DataFrameEditor(parent=parent)
+            editor = DataFrameEditor(
+                parent=parent, data_function=self.make_data_function(index))
             if not editor.setup_and_check(value, title=key):
                 return
             self.create_dialog(editor, dict(model=index.model(), editor=editor,

spyder/plugins/variableexplorer/widgets/objectexplorer/objectexplorer.py

@@ -150,7 +150,8 @@ def set_value(self, obj):
 
         # Tree widget
         old_obj_tree = self.obj_tree
-        self.obj_tree = ToggleColumnTreeView(self.namespacebrowser)
+        self.obj_tree = ToggleColumnTreeView(
+            self.namespacebrowser, self.data_function)
         self.obj_tree.setAlternatingRowColors(True)
         self.obj_tree.setModel(self._proxy_tree_model)
         self.obj_tree.setSelectionBehavior(QAbstractItemView.SelectRows)

spyder/plugins/variableexplorer/widgets/objectexplorer/tests/test_objectexplorer.py

@@ -230,5 +230,53 @@ def datafunc():
     mock_critical.assert_called_once()
 
 
+@dataclass
+class Box:
+    contents: object
+
+
+def test_objectexplorer_refresh_nested():
+    """
+    Open an editor for an `Box` object containing a list, and then open another
+    editor for the nested list. Test that refreshing the second editor works.
+    """
+    old_data = Box([1, 2, 3])
+    new_data = Box([4, 5])
+    editor = ObjectExplorer(
+        old_data, name='data', data_function=lambda: new_data)
+    model = editor.obj_tree.model()
+    root_index = model.index(0, 0)
+    contents_index = model.index(0, 0, root_index)
+    editor.obj_tree.edit(contents_index)
+    delegate = editor.obj_tree.delegate
+    nested_editor = list(delegate._editors.values())[0]['editor']
+    assert nested_editor.get_value() == [1, 2, 3]
+    nested_editor.widget.refresh_action.trigger()
+    assert nested_editor.get_value() == [4, 5]
+
+
+def test_objectexplorer_refresh_doubly_nested():
+    """
+    Open an editor for an `Box` object containing another `Box` object which
+    in turn contains a list. Then open a second editor for the nested list.
+    Test that refreshing the second editor works.
+    """
+    old_data = Box(Box([1, 2, 3]))
+    new_data = Box(Box([4, 5]))
+    editor = ObjectExplorer(
+        old_data, name='data', data_function=lambda: new_data)
+    model = editor.obj_tree.model()
+    root_index = model.index(0, 0)
+    inner_box_index = model.index(0, 0, root_index)
+    editor.obj_tree.expand(inner_box_index)
+    contents_index = model.index(0, 0, inner_box_index)
+    editor.obj_tree.edit(contents_index)
+    delegate = editor.obj_tree.delegate
+    nested_editor = list(delegate._editors.values())[0]['editor']
+    assert nested_editor.get_value() == [1, 2, 3]
+    nested_editor.widget.refresh_action.trigger()
+    assert nested_editor.get_value() == [4, 5]
+
+
 if __name__ == "__main__":
     pytest.main()

spyder/plugins/variableexplorer/widgets/objectexplorer/toggle_column_mixin.py

@@ -10,9 +10,10 @@
 
 # Standard library imports
 import logging
+from typing import Any, Callable, Optional
 
 # Third-party imports
-from qtpy.QtCore import Qt, Signal, Slot
+from qtpy.QtCore import Qt, Slot
 from qtpy.QtWidgets import (QAbstractItemView, QAction, QActionGroup,
                             QHeaderView, QTableWidget, QTreeView, QTreeWidget)
 
@@ -155,12 +156,15 @@ class ToggleColumnTreeView(QTreeView, ToggleColumnMixIn):
     show/hide columns.
     """
 
-    def __init__(self, namespacebrowser=None, readonly=False):
+    def __init__(self, namespacebrowser=None,
+                 data_function: Optional[Callable[[], Any]] = None,
+                 readonly=False):
         QTreeView.__init__(self)
         self.readonly = readonly
         from spyder.plugins.variableexplorer.widgets.collectionsdelegate \
             import ToggleColumnDelegate
-        self.delegate = ToggleColumnDelegate(self, namespacebrowser)
+        self.delegate = ToggleColumnDelegate(
+            self, namespacebrowser, data_function)
         self.setItemDelegate(self.delegate)
         self.setEditTriggers(QAbstractItemView.DoubleClicked)
         self.expanded.connect(self.resize_columns_to_contents)