Resolves issue beeware#197

src/cocoa/toga_cocoa/widgets/optioncontainer.py

@@ -2,14 +2,15 @@
 
 from ..container import Container
 from ..libs import *
+from ..utils import process_callback
 from .base import WidgetMixin
 
 
 class TogaTabViewDelegate(NSObject):
     @objc_method
     def tabView_didSelectTabViewItem_(self, view, item) -> None:
-        pass
-        # print ("Select tab view item")
+        id_tab_view = item.identifier.split('-')[2]
+        process_callback(self._interface._update_current_tab_view(id_tab_view))
 
 
 class OptionContainer(OptionContainerInterface, WidgetMixin):
@@ -23,13 +24,16 @@ def create(self):
         self._impl = NSTabView.alloc().init()
 
         self._delegate = TogaTabViewDelegate.alloc().init()
-        self._delegate.interface = self
+        self._delegate._interface = self
 
         self._impl.setDelegate_(self._delegate)
 
         # Add the layout constraints
         self._add_constraints()
 
+    def _update_current_tab_view(self, value):
+        self._selected = value
+
     def _add_content(self, label, container, widget):
         item = NSTabViewItem.alloc().initWithIdentifier_('%s-Tab-%s' % (id(self), id(widget)))
         item.setLabel_(label)

src/core/toga/interface/widgets/optioncontainer.py

@@ -21,6 +21,7 @@ def __init__(self, id=None, style=None, content=None):
 
         super().__init__(id=id, style=style, content=content)
         self._containers = []
+        self._selected = None
 
     def _configure(self, content):
         if content:
@@ -51,6 +52,19 @@ def add(self, label, widget):
 
         self._add_content(label, container, widget)
 
+    @property
+    def selected(self):
+        """
+        The current id of the tab view selected
+
+        :rtype: ``int``
+        """
+        return self._selected
+
+    @selected.setter
+    def selected(self, value):
+        self._selected = value
+
     def _update_child_layout(self):
         for label, container, widget in self._containers:
             container._update_layout()