Update sample to to show DataViewModel.HasValue usage

demo/DVC_DataViewModel.py

@@ -159,6 +159,16 @@ class MyTreeListModel(dv.PyDataViewModel):
                     return self.ObjectToItem(g)
 
 
+    def HasValue(self, item, col):
+        # Overriding this method allows you to let the view know if there is any
+        # data at all in the cell. If it returns False then GetValue will not be
+        # called for this item and column.
+        node = self.ItemToObject(item)
+        if isinstance(node, Genre) and col > 0:
+            return False
+        return True
+
+
     def GetValue(self, item, col):
         # Return the value to be displayed for this item and column. For this
         # example we'll just pull the values from the data objects we
@@ -168,17 +178,11 @@ class MyTreeListModel(dv.PyDataViewModel):
         node = self.ItemToObject(item)
 
         if isinstance(node, Genre):
-            # We'll only use the first column for the Genre objects,
-            # for the other columns lets just return empty values
-            mapper = { 0 : node.name,
-                       1 : "",
-                       2 : "",
-                       3 : "",
-                       4 : wx.DateTime.FromTimeT(0),  # TODO: There should be some way to indicate a null value...
-                       5 : False,
-                       }
-            return mapper[col]
-
+            # Due to the HasValue implementation above, GetValue should only
+            # be called for the first column for Genre objects. We'll verify
+            # that with this assert.
+            assert col == 0, "Unexpected column value for Genre objects"
+            return node.name
 
         elif isinstance(node, Song):
             mapper = { 0 : node.genre,