WX_UNIT_TEXT can handle default value.

common/wxunittext.cpp

@@ -101,13 +101,15 @@ void WX_UNIT_TEXT::SetUnits( EDA_UNITS_T aUnits, bool aConvert )
 
 void WX_UNIT_TEXT::SetValue( double aValue )
 {
-    assert( aValue >= 0.0 );
-
     if( aValue >= 0.0 )
     {
         m_inputValue->SetValue( wxString( Double2Str( aValue ).c_str(), wxConvUTF8 ) );
         m_inputValue->MarkDirty();
     }
+    else
+    {
+        m_inputValue->SetValue( DEFAULT_VALUE );
+    }
 }
 
 
@@ -169,6 +171,9 @@ boost::optional<double> WX_UNIT_TEXT::GetValue() const
     wxString text = m_inputValue->GetValue();
     double value;
 
+    if( text == DEFAULT_VALUE )
+        return boost::optional<double>( -1.0 );
+
     if( !text.ToDouble( &value ) )
         return boost::optional<double>();
 
@@ -189,3 +194,6 @@ void WX_UNIT_TEXT::onSpinDownEvent( wxSpinEvent& aEvent )
     if( newValue >= 0.0 )
         SetValue( newValue );
 }
+
+
+const wxString WX_UNIT_TEXT::DEFAULT_VALUE = _( "default ");

include/wxunittext.h

@@ -136,6 +136,9 @@ protected:
 
     ///> Step size (added/subtracted difference if spin buttons are used).
     double          m_step;
+
+    ///> Default value (or non-specified)
+    static const wxString DEFAULT_VALUE;
 };
 
 #endif /* WXUNITTEXT_H_ */