persist linked state with the dock layout

enaml/layout/dock_layout.py

@@ -37,6 +37,10 @@ class dockitem(Atom):
     #: if the dock item is a floating item.
     maximized = Bool(False)
 
+    #: Whether or not the item is linked with its proximal neighbors.
+    #: This only has an effect if the dock item is a floating item.
+    linked = Bool(False)
+
     def __init__(self, name, **kwargs):
         """ Initialize an item.
 
@@ -231,6 +235,10 @@ class dockarea(Atom):
     #: The name of the dock item that is maximized in the dock area.
     maximized_item = Unicode()
 
+    #: Whether or not the area is linked with its proximal neighbors.
+    #: This only has an effect if the dock area is a floating area.
+    linked = Bool(False)
+
     #: The child layout node for the area.
     child = Coerced(_areanode)
 

enaml/qt/docking/dock_manager.py

@@ -290,6 +290,7 @@ def save_layout(self):
                     item.maximized_item = maxed.objectName()
             else:
                 item = save_layout(frame)
+            item.linked = frame.isLinked()
             item.maximized = frame.isMaximized()
             if frame.isMaximized():
                 geo = frame.normalGeometry()
@@ -380,6 +381,7 @@ def popuplate_area(area, layout):
             popuplate_area(win_area, item)
             win_area.installEventFilter(self._area_filter)
             self._dock_frames.append(target)
+            self._proximity_handler.addFrame(target)
             targets.append((target, item))
 
         for target, item in targets:
@@ -388,6 +390,8 @@ def popuplate_area(area, layout):
                 rect = ensure_on_screen(rect)
                 target.setGeometry(rect)
             target.show()
+            if item.linked:
+                target.setLinked(True)
             if item.maximized:
                 target.showMaximized()