Refs #6616. Clear error only when the parameter was really changed

Code/Mantid/QtPropertyBrowser/src/DoubleEditorFactory.cpp

@@ -38,9 +38,7 @@ DoubleEditor::~DoubleEditor()
 
 void DoubleEditor::setValue(const double& d)
 {
-  double absVal = fabs(d);
-  char format = absVal > 1e5 || (absVal != 0 && absVal < 1e-5) ? 'e' : 'f';
-  setText(QString::number(d,format , m_decimals));
+  setText(formatValue(d));
 }
 
 void DoubleEditor::updateProperty()
@@ -52,13 +50,35 @@ void DoubleEditor::updateProperty()
   }
 }
 
+/**
+ * @param d :: The value to format
+ * @return Formatted string representation of the value
+ */
+QString DoubleEditor::formatValue(const double& d) const
+{
+  // XXX: this is taken from QtDoublePropertyManager. Ideally, QtDoublePropertyManager should be
+  //      refactored to haves such a method, but it doesn't seem to be a good idea to edit it heavily.
+  double absVal = fabs(d);
+  char format = absVal > 1e5 || (absVal != 0 && absVal < 1e-5) ? 'e' : 'f';
+  return QString::number(d, format, m_decimals);
+}
+
 void ParameterEditor::updateProperty()
 {
   auto mgr = dynamic_cast<ParameterPropertyManager*>(m_property->propertyManager());
   if (mgr)
   {
-    // As the property get supdated, the error becomes invalid, so clear it
-    mgr->clearError(m_property);
+    // To find out whether the value was really changed, we format it and compare string values. This
+    // ensures that we don't suffer from double precision loss and consider only real changes in value
+
+    QString prevVal = formatValue(mgr->value(m_property));
+    QString newVal = formatValue(text().toDouble());
+
+    if ( prevVal != newVal )
+    {
+      // As the value was changed, the error becomes invalid, so clear it
+      mgr->clearError(m_property);
+    }
   }
 
   DoubleEditor::updateProperty();

Code/Mantid/QtPropertyBrowser/src/DoubleEditorFactory.h

@@ -53,6 +53,9 @@ class QT_QTPROPERTYBROWSER_EXPORT DoubleEditor: public QLineEdit
 protected slots:
   virtual void updateProperty();
 protected:
+  /// Returns string representation of the value, using the format of the property
+  QString formatValue(const double& d) const;
+
   QtProperty* m_property;
   int m_decimals;
 };