Fix #707 (stepping in line edits and spin boxes does not work)

The step up/down feature of TaurusValueLineEdit (e.g. using
the up/down keys or the arrows of a TaurusValueSpinBox) was broken when
merging #669 which implemented fragments support in
TaurusValueLineEdit for allowing the display of the wvalue without units
Now we see that supporting fragments generically in TaurusValueLineEdit
is problematic (e.g. it makes little sense to use "rvalue" as a
fragment since "wvalue" will be modified when eventually applying).
Therefore for now limit the fragment support in line edits
to the "wvalue.magnitude" case.

Also fix a hook error introduced in some previous merge.

lib/taurus/qt/qtgui/input/tauruslineedit.py

@@ -109,20 +109,20 @@ def handleEvent(self, evt_src, evt_type, evt_value):
         # handle the case in which the line edit is not yet initialized
         if self._last_value is None:
             try:
-                self.getModelObj().read(cache=True)
-                frag_name = self.modelFragmentName or 'wvalue'
-                value = self.getModelFragmentObj(fragmentName=frag_name)
-                self.debug('Overwriting wvalue=None with %s' % (value))
-                self.setValue(value)
-                self.setEnabled(value is not None)
+                value = self.getModelObj().read(cache=True)
+                self._updateValidator(value)
+                self.setValue(value.wvalue)
             except Exception as e:
-                self.debug('Failed attempt to initialize value: %r', e)
+                self.info('Failed attempt to initialize value: %r', e)
 
         self.setEnabled(evt_type != TaurusEventType.Error)
+
         if evt_type in (TaurusEventType.Change, TaurusEventType.Periodic):
             self._updateValidator(evt_value)
+
         TaurusBaseWritableWidget.handleEvent(
             self, evt_src, evt_type, evt_value)
+
         if evt_type == TaurusEventType.Error:
             self.updateStyle()
 
@@ -215,36 +215,18 @@ def _stepBy(self, v):
         value = self.getValue()
         self.setValue(value + Quantity(v, value.units))
 
-    def getDisplayValue(self, cache=True, fragmentName=None):
-        """Returns a string representation of the model value associated with
-        this component. As this is a writable widget, if there is no fragment
-        specified, the default behaviour is to display the wvalue.
-
-        :param cache: (bool) (ignored, just for bck-compat).
-        :param fragmentName: (str or None) the returned value will correspond
-                        to the given fragmentName. If None passed,
-                         self.modelFragmentName will be used, and if None is
-                         set, the defaultFragmentName of the model will be used
-                         instead.
-
-        :return: (str) a string representation of the model value.
-        """
-        if fragmentName is None and self.modelFragmentName is None:
-            return TaurusBaseWritableWidget.getDisplayValue(
-                self, cache=cache, fragmentName='wvalue')
-        else:
-            return TaurusBaseWritableWidget.getDisplayValue(
-                self, cache=cache, fragmentName=fragmentName)
-
     def setValue(self, v):
-        model = self.getModelObj()
-        if model is None:
-            v_str = str(v)
-        else:
-            v_str = str(self.getDisplayValue(v))
-        v_str = v_str.strip()
+        """Set the displayed text from a given value object"""
+        # Support displaying the value without units (enabled by fragment)
+        # Other fragments are ignored by setValue
+        if self.modelFragmentName == "wvalue.magnitude":
+            try:
+                units = self.validator().units
+                v = v.to(units).magnitude
+            except Exception as e:
+                self.debug('Cannot enforce fragment. Reason: %r', e)
         self._last_value = v
-        self.setText(v_str)
+        self.setText(str(self.displayValue(v)).strip())
 
     def getValue(self):
         text = self.text()