Add 'Select data' message to combos

glue/core/data_combo_helper.py

@@ -49,13 +49,38 @@ class ComboHelper(HubListener):
         The state to which the selection property belongs
     selection_property : :class:`~glue.external.echo.SelectionCallbackProperty`
         The selection property representing the combo.
+    none : bool or str, optional
+        Add an entry that means `None`. If a string, this is the display string
+        that will be shown for the `None` entry, otherwise an empty string is
+        shown.
     """
 
-    def __init__(self, state, selection_property):
+    def __init__(self, state, selection_property, none=False):
+
+        if isinstance(none, string_types):
+            self._none = True
+            self._none_label = none
+        else:
+            self._none = none
+            self._none_label = ''
 
         self._state = weakref.ref(state)
         self.selection_property = selection_property
 
+    @property
+    def none(self):
+        return self._none
+
+    @none.setter
+    def none(self, value):
+        if isinstance(value, string_types):
+            self._none = True
+            self._none_label = value
+        else:
+            self._none = value
+            self._none_label = ''
+        self.refresh()
+
     @property
     def state(self):
         """
@@ -86,6 +111,8 @@ def choices(self):
     def choices(self, choices):
         with delay_callback(self.state, self.selection_property):
             prop = getattr(type(self.state), self.selection_property)
+            if self._none:
+                choices = [None] + choices
             prop.set_choices(self.state, choices)
 
     @property
@@ -100,7 +127,15 @@ def display(self):
     @display.setter
     def display(self, display):
         prop = getattr(type(self.state), self.selection_property)
-        return prop.set_display_func(self.state, display)
+        if self._none:
+            def display_wrapper(value):
+                if value is None:
+                    return self._none_label
+                else:
+                    return display(value)
+            return prop.set_display_func(self.state, display_wrapper)
+        else:
+            return prop.set_display_func(self.state, display)
 
     def _on_rename(self, msg):
         # If a component ID is renamed, we don't need to refresh because the
@@ -160,20 +195,10 @@ def __init__(self, state, selection_property,
                  numeric=True, categorical=True,
                  pixel_coord=False, world_coord=False, derived=True, none=False):
 
-        super(ComponentIDComboHelper, self).__init__(state, selection_property)
-
-        if isinstance(none, string_types):
-            self._none = True
-            self._none_label = none
-        else:
-            self._none = none
-            self._none_label = ''
+        super(ComponentIDComboHelper, self).__init__(state, selection_property, none=none)
 
         def display_func_label(cid):
-            if cid is None:
-                return self._none_label
-            else:
-                return cid.label
+            return cid.label
 
         self.display = display_func_label
 
@@ -251,20 +276,6 @@ def derived(self, value):
         self._derived = value
         self.refresh()
 
-    @property
-    def none(self):
-        return self._none
-
-    @none.setter
-    def none(self, value):
-        if isinstance(value, string_types):
-            self._none = True
-            self._none_label = value
-        else:
-            self._none = value
-            self._none_label = ''
-        self.refresh()
-
     def append_data(self, data, refresh=True):
 
         if self._manual_data:
@@ -331,9 +342,6 @@ def refresh(self, *args):
 
         choices = []
 
-        if self._none:
-            choices.append(None)
-
         for data in self._data:
 
             derived_components = [cid for cid in data.derived_components if cid.parent is data]
@@ -412,11 +420,15 @@ class BaseDataComboHelper(ComboHelper):
         The data collection to which the datasets belong - this is needed
         because if a dataset is removed from the data collection, we want to
         remove it here.
+    none : bool or str, optional
+        Add an entry that means `None`. If a string, this is the display string
+        that will be shown for the `None` entry, otherwise an empty string is
+        shown.
     """
 
-    def __init__(self, state, selection_property, data_collection=None):
+    def __init__(self, state, selection_property, data_collection=None, none=False):
 
-        super(BaseDataComboHelper, self).__init__(state, selection_property)
+        super(BaseDataComboHelper, self).__init__(state, selection_property, none=none)
 
         def display_func_label(cid):
             return cid.label
@@ -562,10 +574,10 @@ class DataCollectionComboHelper(BaseDataComboHelper):
         The data collection with which to stay in sync
     """
 
-    def __init__(self, state, selection_property, data_collection):
+    def __init__(self, state, selection_property, data_collection, none=False):
 
         super(DataCollectionComboHelper, self).__init__(state, selection_property,
-                                                        data_collection=data_collection)
+                                                        data_collection=data_collection, none=none)
 
         self._datasets = data_collection
 

glue/dialogs/component_arithmetic/qt/component_arithmetic.py

@@ -6,19 +6,20 @@
 from qtpy import QtWidgets, QtGui
 from qtpy.QtCore import Qt
 
-from glue.external.echo import SelectionCallbackProperty
+from glue.external.echo import SelectionCallbackProperty, HasCallbackProperties
 from glue.external.echo.qt import connect_combo_selection
 from glue.core import ComponentID
 from glue.core.parse import ParsedComponentLink, ParsedCommand
 from glue.utils.qt import load_ui
 from glue.core.message import NumericalDataChangedMessage
+from glue.core.data_combo_helper import DataCollectionComboHelper
 
 from glue.dialogs.component_arithmetic.qt.equation_editor import EquationEditorDialog
 
 __all__ = ['ArithmeticEditorWidget']
 
 
-class ArithmeticEditorWidget(QtWidgets.QDialog):
+class ArithmeticEditorWidget(QtWidgets.QDialog, HasCallbackProperties):
 
     data = SelectionCallbackProperty()
 
@@ -63,8 +64,8 @@ def __init__(self, data_collection=None, parent=None):
                     self._components_other[data].append(cid)
 
         # Populate data combo
-        ArithmeticEditorWidget.data.set_choices(self, list(self.data_collection))
-        ArithmeticEditorWidget.data.set_display_func(self, lambda x: x.label)
+        self._data_helper = DataCollectionComboHelper(self, 'data', data_collection,
+                                                      none='Select dataset')
         connect_combo_selection(self, 'data', self.ui.combosel_data)
 
         self.ui.combosel_data.setCurrentIndex(0)
@@ -98,11 +99,16 @@ def _update_component_lists(self, *args):
 
         self.list.blockSignals(True)
 
+        self.list.clear()
+
+        if self.data is None:
+            return
+
         mapping = {}
         for cid in self.data.components:
             mapping[cid] = cid.label
 
-        self.list.clear()
+
         for cid in self._components_derived[self.data]:
             label = self._state[self.data][cid]['label']
             if self._state[self.data][cid]['equation'] is None: