Resolve "Create SFG in GUI"

Closes #86 (closed)

b_asic/GUI/arrow.py

@@ -5,12 +5,14 @@ QGraphicsLineItem, QGraphicsWidget
 from PySide2.QtCore import Qt, QSize, QLineF, QPoint, QRectF
 from PySide2.QtGui import QIcon, QFont, QPainter, QPen
 
+from b_asic import Signal 
 
 class Arrow(QGraphicsLineItem):
 
     def __init__(self, source, destination, window, parent=None):
         super(Arrow, self).__init__(parent)
         self.source = source
+        self.signal = Signal(source.port, destination.port)
         self.destination = destination
         self._window = window
         self.moveLine()