diff --git a/wxPython/demo/Main.py b/wxPython/demo/Main.py
index c5ec3fa129..45f8255b31 100644
--- a/wxPython/demo/Main.py
+++ b/wxPython/demo/Main.py
@@ -70,6 +70,7 @@ _treeList = [
         'SearchCtrl',
         'SizedControls',
         'AUI_MDI',
+        'TreeMixin',
         ]),
 
     # managed windows == things with a (optional) caption you can close
@@ -214,6 +215,7 @@ _treeList = [
         'Throbber',
         'Ticker',
         'TimeCtrl',
+        'TreeMixin',
         'VListBox',
         ]),
 
diff --git a/wxPython/demo/TreeMixin.py b/wxPython/demo/TreeMixin.py
new file mode 100644
index 0000000000..556cf2ad14
--- /dev/null
+++ b/wxPython/demo/TreeMixin.py
@@ -0,0 +1,230 @@
+import wx, wx.lib.customtreectrl, wx.gizmos
+import wx.lib.mixins.treemixin as treemixin
+
+class TreeModel(object):
+    def __init__(self, *args, **kwargs):
+        self.items = []
+        self.itemCounter = 0
+        super(TreeModel, self).__init__(*args, **kwargs)
+
+    def GetItem(self, indices):
+        text, children = 'Hidden root', self.items
+        for index in indices:
+            text, children = children[index]
+        return text, children
+
+    def GetText(self, indices):
+        return self.GetItem(indices)[0]
+
+    def GetChildren(self, indices):
+        return self.GetItem(indices)[1]
+
+    def GetChildrenCount(self, indices):
+        return len(self.GetChildren(indices))
+
+    def SetChildrenCount(self, indices, count):
+        children = self.GetChildren(indices)
+        while len(children) > count:
+            children.pop()
+        while len(children) < count:
+            children.append(('item %d'%self.itemCounter, []))
+            self.itemCounter += 1
+
+    def MoveItem(self, itemToMoveIndices, newParentIndices):
+        itemToMove = self.GetItem(itemToMoveIndices)
+        newParentChildren = self.GetChildren(newParentIndices)
+        newParentChildren.append(itemToMove)
+        oldParentChildren = self.GetChildren(itemToMoveIndices[:-1])
+        oldParentChildren.remove(itemToMove)
+
+
+class DemoVirtualTreeMixin(treemixin.VirtualTree, treemixin.DragAndDrop):
+    def __init__(self, *args, **kwargs):
+        self.model = kwargs.pop('treemodel')
+        self.log = kwargs.pop('log')
+        super(DemoVirtualTreeMixin, self).__init__(*args, **kwargs)
+        self.CreateImageList()
+
+    def CreateImageList(self):
+        size = (16, 16)
+        self.imageList = wx.ImageList(*size)
+        for art in wx.ART_FOLDER, wx.ART_FILE_OPEN, wx.ART_NORMAL_FILE:
+            self.imageList.Add(wx.ArtProvider.GetBitmap(art, wx.ART_OTHER, 
+                                                        size))
+        self.AssignImageList(self.imageList)
+
+    def OnGetItemText(self, indices):
+        return self.model.GetText(indices)
+
+    def OnGetChildrenCount(self, indices):
+        return self.model.GetChildrenCount(indices)
+
+    def OnGetItemFont(self, indices):
+        if self.model.GetChildrenCount(indices) > 0:
+            return wx.SMALL_FONT
+        else:
+            return super(DemoVirtualTreeMixin, self).OnGetItemFont(indices)
+
+    def OnGetItemTextColour(self, indices):
+        if len(indices) % 2 == 0:
+            return wx.RED
+        elif len(indices) % 3 == 0:
+            return wx.BLUE
+        else:
+            return super(DemoVirtualTreeMixin, 
+                         self).OnGetItemTextColour(indices)
+
+    def OnGetItemBackgroundColour(self, indices):
+        if indices[-1] == len(indices):
+            return wx.GREEN
+        else: 
+            return super(DemoVirtualTreeMixin, 
+                         self).OnGetItemBackgroundColour(indices)
+
+    def OnGetItemImage(self, indices, which):
+        if which in [wx.TreeItemIcon_Normal, wx.TreeItemIcon_Selected]:
+            if self.model.GetChildrenCount(indices):
+                return 0
+            else:
+                return 2
+        else:
+            return 1
+
+    def OnDrop(self, dropTarget, dragItem):
+        dropIndices = self.ItemIndices(dropTarget)
+        dropText = self.model.GetText(dropIndices)
+        dragIndices = self.ItemIndices(dragItem)
+        dragText = self.model.GetText(dragIndices)
+        self.log.write('drop %s %s on %s %s'%(dragText, dragIndices,
+            dropText, dropIndices))
+        self.model.MoveItem(dragIndices, dropIndices)
+        self.GetParent().RefreshItems()
+
+
+class VirtualTreeCtrl(DemoVirtualTreeMixin, wx.TreeCtrl):
+    pass
+
+
+class VirtualTreeListCtrl(DemoVirtualTreeMixin, wx.gizmos.TreeListCtrl):
+    def __init__(self, *args, **kwargs):
+        kwargs['style'] = wx.TR_DEFAULT_STYLE | wx.TR_FULL_ROW_HIGHLIGHT
+        super(VirtualTreeListCtrl, self).__init__(*args, **kwargs)
+        self.AddColumn('Column 0')
+        self.AddColumn('Column 1')
+        for art in wx.ART_TIP, wx.ART_WARNING:
+            self.imageList.Add(wx.ArtProvider.GetBitmap(art, wx.ART_OTHER, 
+                                                        (16, 16)))
+
+    def OnGetItemText(self, indices, column=0):
+        return '%s, column %d'%\
+            (super(VirtualTreeListCtrl, self).OnGetItemText(indices), column)
+
+    def OnGetItemImage(self, indices, which, column=0):
+        if column == 0:
+            return super(VirtualTreeListCtrl, self).OnGetItemImage(indices, 
+                                                                   which)
+        elif self.OnGetChildrenCount(indices):
+            return 4
+        else:
+            return 3
+
+
+class VirtualCustomTreeCtrl(DemoVirtualTreeMixin, 
+                            wx.lib.customtreectrl.CustomTreeCtrl):
+    def __init__(self, *args, **kwargs):
+        self.checked = {}
+        kwargs['ctstyle'] = wx.TR_DEFAULT_STYLE | wx.TR_HIDE_ROOT | \
+                            wx.TR_HAS_BUTTONS | wx.TR_FULL_ROW_HIGHLIGHT
+        super(VirtualCustomTreeCtrl, self).__init__(*args, **kwargs)
+        self.Bind(wx.lib.customtreectrl.EVT_TREE_ITEM_CHECKED,
+                  self.OnItemChecked)
+
+    def OnGetItemType(self, indices):
+        if len(indices) == 1:
+            return 1
+        elif len(indices) == 2:
+            return 2
+        else:
+            return 0
+
+    def OnGetItemChecked(self, indices):
+        return self.checked.get(tuple(indices), False)
+
+    def OnItemChecked(self, event):
+        item = event.GetItem()
+        indices = tuple(self.ItemIndices(item))
+        if self.GetItemType(item) == 2: 
+            # It's a radio item; reset other items on the same level
+            for index in range(self.GetChildrenCount(self.GetItemParent(item))):
+                self.checked[indices[:-1]+(index,)] = False
+        self.checked[indices] = True
+
+
+
+class TreeNotebook(wx.Notebook):
+    def __init__(self, *args, **kwargs):
+        treemodel = kwargs.pop('treemodel')
+        log = kwargs.pop('log')
+        super(TreeNotebook, self).__init__(*args, **kwargs)
+        self.trees = []
+        for class_, title in [(VirtualTreeCtrl, 'TreeCtrl'),
+                              (VirtualTreeListCtrl, 'TreeListCtrl'),
+                              (VirtualCustomTreeCtrl, 'CustomTreeCtrl')]:
+            tree = class_(self, treemodel=treemodel, log=log)
+            self.trees.append(tree)
+            self.AddPage(tree, title)
+        self.RefreshItems()
+
+    def RefreshItems(self):
+        for tree in self.trees:
+            tree.RefreshItems()
+            tree.UnselectAll()
+
+    def GetSelectedItemIndices(self):
+        tree = self.trees[self.GetSelection()]
+        if tree.GetSelection():
+            return tree.ItemIndices(tree.GetSelection())
+        else:
+            return []
+
+
+class TestPanel(wx.Panel):
+    def __init__(self, parent, log):
+        self.log = log
+        super(TestPanel, self).__init__(parent)
+        self.treemodel = TreeModel()
+        self.notebook = TreeNotebook(self, treemodel=self.treemodel, log=log)
+        label = wx.StaticText(self, label='Number of children: ')
+        self.childrenCountCtrl = wx.SpinCtrl(self, value='0', max=10000)
+        button = wx.Button(self, label='Update children')
+        button.Bind(wx.EVT_BUTTON, self.onEnter)
+        hSizer = wx.BoxSizer(wx.HORIZONTAL)
+        options = dict(flag=wx.ALIGN_CENTER_VERTICAL|wx.ALL, border=2)
+        hSizer.Add(label, **options)
+        hSizer.Add(self.childrenCountCtrl, 2, **options)
+        hSizer.Add(button, **options)
+        sizer = wx.BoxSizer(wx.VERTICAL)
+        sizer.Add(self.notebook, 1, wx.EXPAND)
+        sizer.Add(hSizer, 0, wx.EXPAND)
+        self.SetSizer(sizer)
+
+    def onEnter(self, event):
+        indices = self.notebook.GetSelectedItemIndices()
+        text = self.treemodel.GetText(indices)
+        oldChildrenCount = self.treemodel.GetChildrenCount(indices)
+        newChildrenCount = self.childrenCountCtrl.GetValue()
+        self.log.write('%s %s now has %d children (was %d)'%(text, indices,
+            newChildrenCount, oldChildrenCount))
+        self.treemodel.SetChildrenCount(indices, newChildrenCount)
+        self.notebook.RefreshItems()
+
+
+def runTest(frame, nb, log):
+    win = TestPanel(nb, log)
+    return win
+
+
+if __name__ == '__main__':
+    import sys, os, run
+    run.main(['', os.path.basename(sys.argv[0])] + sys.argv[1:])
+
diff --git a/wxPython/docs/CHANGES.txt b/wxPython/docs/CHANGES.txt
index 14671a6844..123405ab4d 100644
--- a/wxPython/docs/CHANGES.txt
+++ b/wxPython/docs/CHANGES.txt
@@ -14,6 +14,8 @@ Refactored the inspection tool such that it can be used as a wx.App
 mix-in class as it was used before (with the wx.lib.mixins.inspect
 module) and also as a non mix-in tool (using wx.lib.inspect.InspectionTool). 
 
+Add wx.lib.mixins.treemixin from Frank Niessink.
+
 
 
 
diff --git a/wxPython/tests/TreeMixinTest.py b/wxPython/tests/TreeMixinTest.py
new file mode 100644
index 0000000000..992c032aed
--- /dev/null
+++ b/wxPython/tests/TreeMixinTest.py
@@ -0,0 +1,237 @@
+import wx, wx.gizmos, wx.lib.customtreectrl, unittest, treemixin
+
+
+class VirtualTreeCtrl(treemixin.VirtualTree, wx.TreeCtrl):
+    def __init__(self, *args, **kwargs):
+        self.children = {}
+        super(VirtualTreeCtrl, self).__init__(*args, **kwargs)
+
+    def OnGetItemText(self, indices):
+        return 'item %s'%'.'.join([str(index) for index in indices])
+
+    def OnGetChildrenCount(self, indices=None):
+        indices = indices or []
+        return self.children.get(tuple(indices), 0)
+
+    def SetChildrenCount(self, indices, childrenCount):
+        self.children[tuple(indices)] = childrenCount 
+
+
+class VirtualTreeCtrlTest_NoRootItems(unittest.TestCase):
+    def setUp(self):
+        self.frame = wx.Frame(None)
+        self.tree = VirtualTreeCtrl(self.frame)
+        self.tree.RefreshItems()
+
+    def testNoRootItems(self):
+        self.assertEqual(0, self.tree.GetCount())
+
+    def testAddTwoRootItems(self):
+        self.tree.SetChildrenCount([], 2)
+        self.tree.RefreshItems()
+        self.assertEqual(2, self.tree.GetCount())
+
+    def testAddOneRootItemAndOneChild(self):
+        self.tree.SetChildrenCount([], 1)
+        self.tree.SetChildrenCount([0], 1)
+        self.tree.RefreshItems()
+        self.tree.ExpandAll()
+        self.assertEqual(2, self.tree.GetCount())
+
+    def testAddOneRootItemAndTwoChildren(self):
+        self.tree.SetChildrenCount([], 1)
+        self.tree.SetChildrenCount([0], 2)
+        self.tree.RefreshItems()
+        self.tree.ExpandAll()
+        self.assertEqual(3, self.tree.GetCount())
+
+
+class VirtualTreeCtrlTest_OneRoot(unittest.TestCase):
+    def setUp(self):
+        self.frame = wx.Frame(None)
+        self.tree = VirtualTreeCtrl(self.frame)
+        self.tree.SetChildrenCount([], 1)
+        self.tree.RefreshItems()
+
+    def testOneRoot(self):
+        self.assertEqual(1, self.tree.GetCount())
+
+    def testDeleteRootItem(self):
+        self.tree.SetChildrenCount([], 0)
+        self.tree.RefreshItems()
+        self.assertEqual(0, self.tree.GetCount())
+
+    def testAddOneChild(self):
+        self.tree.SetChildrenCount([0], 1)
+        self.tree.RefreshItems()
+        self.tree.ExpandAll()
+        self.assertEqual(2, self.tree.GetCount())
+
+    def testAddTwoChildren(self):
+        self.tree.SetChildrenCount([0], 2)
+        self.tree.RefreshItems()
+        self.tree.ExpandAll()
+        self.assertEqual(3, self.tree.GetCount())
+
+
+
+class TreeAPIHarmonizerTestCase(unittest.TestCase):
+    style = wx.TR_DEFAULT_STYLE
+
+    def setUp(self):
+        self.frame = wx.Frame(None)
+        class HarmonizedTreeCtrl(treemixin.TreeAPIHarmonizer, self.TreeClass):
+            pass
+        self.tree = HarmonizedTreeCtrl(self.frame, style=self.style)
+        self.populateTree()
+
+    def populateTree(self):
+        self.root = self.tree.AddRoot('Root')
+        self.item = self.tree.AppendItem(self.root, 'item')
+
+
+class TreeAPIHarmonizerCommonTests(object):
+    def testSetItemImage(self):
+        self.tree.SetItemImage(self.item, -1, wx.TreeItemIcon_Normal)
+        self.assertEqual(-1, 
+            self.tree.GetItemImage(self.item, wx.TreeItemIcon_Normal))
+
+    def testGetColumnCount(self):
+        self.assertEqual(0, self.tree.GetColumnCount())
+
+    def testGetItemType(self):
+        self.assertEqual(0, self.tree.GetItemType(self.item))
+
+    def testGetMainWindow(self):
+        self.assertEqual(self.tree, self.tree.GetMainWindow())
+
+
+class TreeAPIHarmonizerSingleSelectionTests(object):
+    def testUnselectAll(self):
+        self.tree.SelectItem(self.item)
+        self.tree.UnselectAll()
+        self.assertEqual([], self.tree.GetSelections())
+
+    def testGetSelections_NoSelection(self):
+        self.tree.UnselectAll()
+        self.assertEqual([], self.tree.GetSelections())
+
+    def testGetSelections_OneSelectedItem(self):
+        self.tree.UnselectAll()
+        self.tree.SelectItem(self.item)
+        self.assertEqual([self.item], self.tree.GetSelections())
+
+
+class TreeAPIHarmonizerMultipleSelectionTests(object):
+    style = wx.TR_DEFAULT_STYLE | wx.TR_MULTIPLE
+    
+    def testUnselectAll(self):
+        self.tree.SelectItem(self.item)
+        self.tree.UnselectAll()
+        self.assertEqual([], self.tree.GetSelections())
+
+    def testGetSelections_NoSelection(self):
+        self.tree.UnselectAll()
+        self.assertEqual([], self.tree.GetSelections())
+
+    def testGetSelections_OneSelectedItem(self):
+        self.tree.UnselectAll()
+        self.tree.SelectItem(self.item)
+        self.assertEqual([self.item], self.tree.GetSelections())
+
+    def testGetSelections_TwoSelectedItems(self):
+        self.tree.UnselectAll()
+        item2 = self.tree.AppendItem(self.root, 'item 2')
+        self.tree.SelectItem(self.item)
+        self.tree.SelectItem(item2)
+        self.assertEqual([self.item, item2], self.tree.GetSelections())
+
+
+class TreeAPIHarmonizerWithTreeCtrlTestCase(TreeAPIHarmonizerTestCase):
+    TreeClass = wx.TreeCtrl
+
+class TreeAPIHarmonizerWithTreeCtrl_SingleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerSingleSelectionTests,
+        TreeAPIHarmonizerWithTreeCtrlTestCase):
+    pass
+
+class TreeAPIHarmonizerWithTreeCtrl_MultipleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerMultipleSelectionTests, 
+        TreeAPIHarmonizerWithTreeCtrlTestCase):
+    pass
+
+
+class TreeAPIHarmonizerWithTreeListCtrlTestCase(TreeAPIHarmonizerTestCase):
+    TreeClass = wx.gizmos.TreeListCtrl
+
+    def populateTree(self):
+        self.tree.AddColumn('Column')
+        super(TreeAPIHarmonizerWithTreeListCtrlTestCase, self).populateTree()
+
+
+class TreeAPIHarmonizerWithTreeListCtrl_SingleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerSingleSelectionTests,
+        TreeAPIHarmonizerWithTreeListCtrlTestCase):
+
+    def testGetColumnCount(self):
+        self.assertEqual(1, self.tree.GetColumnCount())
+
+    def testGetMainWindow(self):
+        self.assertNotEqual(self.tree, self.tree.GetMainWindow())
+
+
+class TreeAPIHarmonizerWithTreeListCtrl_MultipleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerMultipleSelectionTests,
+        TreeAPIHarmonizerWithTreeListCtrlTestCase):
+
+    def testGetColumnCount(self):
+        self.assertEqual(1, self.tree.GetColumnCount())
+
+    def testGetMainWindow(self):
+        self.assertNotEqual(self.tree, self.tree.GetMainWindow())
+
+    def testGetSelections_TwoSelectedItems(self):
+        ''' Override TreeAPIHarmonizerMultipleSelectionTests.-
+            testGetSelections_TwoSelectedItems, because 
+            TreeListCtrl.SelectItem needs an extra parameter. '''
+        self.tree.UnselectAll()
+        item2 = self.tree.AppendItem(self.root, 'item 2')
+        self.tree.SelectItem(self.item)
+        self.tree.SelectItem(item2, unselect_others=False)
+        self.assertEqual([self.item, item2], self.tree.GetSelections())
+
+
+class TreeAPIHarmonizerWithCustomTreeCtrlTestCase(TreeAPIHarmonizerTestCase):
+    TreeClass = wx.lib.customtreectrl.CustomTreeCtrl
+
+
+class TreeAPIHarmonizerCustomTreeCtrlTests(object):
+    def testGetCheckItemType(self):
+        item = self.tree.AppendItem(self.root, 'item', ct_type=1)
+        self.assertEqual(1, self.tree.GetItemType(item))
+
+    def testGetRadioItemType(self):
+        item = self.tree.AppendItem(self.root, 'item', ct_type=2)
+        self.assertEqual(2, self.tree.GetItemType(item))
+
+
+class TreeAPIHarmonizerWithCustomTreeCtrl_SingleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerSingleSelectionTests,
+        TreeAPIHarmonizerCustomTreeCtrlTests,
+        TreeAPIHarmonizerWithCustomTreeCtrlTestCase):
+    pass
+
+
+class TreeAPIHarmonizerWithCustomTreeCtrl_MultipleSelection( \
+        TreeAPIHarmonizerCommonTests, TreeAPIHarmonizerMultipleSelectionTests,
+        TreeAPIHarmonizerCustomTreeCtrlTests,
+        TreeAPIHarmonizerWithCustomTreeCtrlTestCase):
+    pass
+
+
+
+if __name__ == '__main__':
+    app = wx.App(False)
+    unittest.main()
+
+
diff --git a/wxPython/wx/lib/mixins/treemixin.py b/wxPython/wx/lib/mixins/treemixin.py
new file mode 100644
index 0000000000..79dc6be3fc
--- /dev/null
+++ b/wxPython/wx/lib/mixins/treemixin.py
@@ -0,0 +1,443 @@
+'''
+treemixin.py 
+
+This module provides two mixin classes that can be used with tree
+controls: 
+- VirtualTree is a class that, when mixed in with a tree control,
+makes the tree control virtual, similar to a ListCtrl in virtual mode. 
+A virtual tree control builds the tree itself by means of callbacks,
+so the programmer is freed from the burden of building the tree herself.
+- DragAndDrop is a mixin class that helps with dragging and dropping of
+items. The graphical part of dragging and dropping tree items is done by
+this mixin class. You only need to implement the OnDrop method that is
+called when the drop happens.
+
+Both mixin classes work with wx.TreeCtrl, wx.gizmos.TreeListCtrl, 
+and wx.lib.customtree.CustomTreeCtrl. They can be used together or 
+separately.
+
+Both mixins force the wx.TR_HIDE_ROOT style.
+
+Frank Niessink <frank@niessink.com>
+License: wxWidgets license
+Version: 0.5
+Date: 11 February 2007
+'''
+
+import wx
+
+class TreeAPIHarmonizer(object):
+    ''' This class attempts to hide the differences in API between the
+    different tree controls currently supported. '''
+
+    def GetColumnCount(self):
+        # Only TreeListCtrl has columns, return 0 if we are mixed in
+        # with another tree control.
+        try:
+            return super(TreeAPIHarmonizer, self).GetColumnCount()
+        except AttributeError:
+            return 0
+
+    def GetItemType(self, item):
+        # Only CustomTreeCtrl has different item types, return the
+        # default item type if we are mixed in with another tree control.
+        try:
+            return super(TreeAPIHarmonizer, self).GetItemType(item)
+        except AttributeError:
+            return 0
+
+    def SetItemImage(self, item, imageIndex, which, column=0):
+        # The SetItemImage signature is different for TreeListCtrl and
+        # other tree controls. This adapter method hides the differences.
+        if self.GetColumnCount():
+            args = (item, imageIndex, column, which)
+        else:
+            args = (item, imageIndex, which)
+        super(TreeAPIHarmonizer, self).SetItemImage(*args)
+
+    def GetMainWindow(self):
+        # Only TreeListCtrl has a separate main window, return self if we are 
+        # mixed in with another tree control.
+        try:
+            return super(TreeAPIHarmonizer, self).GetMainWindow()
+        except AttributeError:
+            return self
+
+    def UnselectAll(self):
+        if self.GetWindowStyle() & wx.TR_MULTIPLE:
+            super(TreeAPIHarmonizer, self).UnselectAll()
+        else:
+            self.Unselect()
+
+    def GetSelections(self):
+        if self.GetWindowStyle() & wx.TR_MULTIPLE:
+            return super(TreeAPIHarmonizer, self).GetSelections()
+        else:
+            selection = self.GetSelection()
+            if selection:
+                return [selection]
+            else:
+                return []
+
+    def HitTest(self, *args, **kwargs):
+        # Only TreeListCtrl has columns, return 0 for the column if we are 
+        # mixed in with another tree control.
+        hitTestResult = super(TreeAPIHarmonizer, self).HitTest(*args, **kwargs)
+        try:
+            item, flags, column = hitTestResult
+        except ValueError:
+            (item, flags), column = hitTestResult, 0
+        return item, flags, column
+
+    def GetItemChildren(self, item, recursively=False):
+        ''' Return the children of item as a list. This method is not
+        part of the API of any tree control, but merely convenient to
+        have available. '''
+        children = []
+        child, cookie = self.GetFirstChild(item)
+        while child:
+            children.append(child)
+            if recursively:
+                children.extend(self.GetItemChildren(child, True))
+            child, cookie = self.GetNextChild(item, cookie)
+        return children
+
+
+class VirtualTree(TreeAPIHarmonizer):
+    ''' This is a mixin class that can be used to allow for virtual tree
+    controls. It can be mixed in with wx.TreeCtrl, wx.gizmos.TreeListCtrl, 
+    wx.lib.customtree.CustomTreeCtrl.
+
+    To use it derive a new class from this class and one of the tree
+    controls, e.g.:
+    class MyTree(VirtualTree, wx.TreeCtrl):
+        ...
+
+    You *must* implement OnGetChildrenCount and OnGetItemText so that
+    this class knows how many items to draw and what text to use. To
+    also draw images, change colours, etc., override one or more of the
+    other OnGetXXX methods.
+
+    About specifying item indices: the VirtualTree uses various item 
+    callbacks (such as OnGetItemText) to retrieve information needed 
+    to display the items. To specify what item a callback needs
+    information about, the callback passes a list of indices. The first
+    index in the list is the index of the root item. If no more indices
+    are in the list (i.e. the length of the list of indices is exactly
+    1), the callback should return the information about that root item.
+    If the list contains two indices, the first index is the index of
+    the root item, and the second index is the index of the child of
+    that root item. For example, if OnGetItemText is called with
+    indices=[0,2], the callback should return information about that the
+    third child of the first root item. OnGetChildrenCount may also be
+    called with indices == [] to get the number of root items in the
+    tree.
+    '''
+
+    def __init__(self, *args, **kwargs):
+        kwargs['style'] = kwargs.get('style', wx.TR_DEFAULT_STYLE) | \
+                          wx.TR_HIDE_ROOT
+        super(VirtualTree, self).__init__(*args, **kwargs)
+        self.Bind(wx.EVT_TREE_ITEM_EXPANDING, self.OnItemExpanding)
+        self.Bind(wx.EVT_TREE_ITEM_COLLAPSED, self.OnItemCollapsed)
+
+    def OnGetChildrenCount(self, indices):
+        ''' This function must be overloaded in the derived class. It
+        should return the number of child items of the item with the
+        provided indices. If indices == [] it should return the number
+        of root items. '''
+        raise NotImplementedError
+
+    def OnGetItemText(self, indices, column=0):
+        ''' This function must be overloaded in the derived class. It 
+        should return the string containing the text of the specified
+        item. '''
+        raise NotImplementedError
+
+    def OnGetItemFont(self, indices):
+        ''' This function may be overloaded in the derived class. It 
+        should return the wx.Font to be used for the specified item. '''
+        return wx.NullFont 
+
+    def OnGetItemTextColour(self, indices):
+        ''' This function may be overloaded in the derived class. It 
+        should return the wx.Colour to be used as text colour for the 
+        specified item. '''
+        return wx.NullColour
+
+    def OnGetItemBackgroundColour(self, indices):
+        ''' This function may be overloaded in the derived class. It 
+        should return the wx.Colour to be used as background colour for 
+        the specified item. '''
+        return wx.NullColour
+
+    def OnGetItemImage(self, indices, which=wx.TreeItemIcon_Normal, column=0):
+        ''' This function may be overloaded in the derived class. It 
+        should return the index of the image to be used. '''
+        return -1
+
+    def OnGetItemType(self, indices):
+        ''' This function may be overloaded in the derived class, but
+        that only makes sense when this class is mixed in with a tree 
+        control that supports checkable items, e.g. CustomTreeCtrl. 
+        This method should return whether the item is to be normal (0,
+        the default), a checkbox (1) or a radiobutton (2). 
+        Note that OnGetItemChecked should return whether the item is
+        actually checked. '''
+        return 0 
+
+    def OnGetItemChecked(self, indices):
+        ''' This function may be overloaded in the derived class, but
+        that only makes sense when this class is mixed in with a tree 
+        control that supports checkable items, e.g. CustomTreeCtrl. 
+        This method should return whether the item is to be checked. 
+        Note that OnGetItemType should return 1 (checkbox) or 2
+        (radiobutton) for this item. '''
+        return False 
+
+    def RefreshItems(self):
+        ''' Redraws all visible items. '''
+        rootItem = self.GetRootItem()
+        if not rootItem:
+            rootItem = self.AddRoot('Hidden root')
+        self.RefreshChildrenRecursively(rootItem, [], 
+                                        self.OnGetChildrenCount([]))
+
+    def RefreshChildrenRecursively(self, item, indices, childrenCount):
+        ''' Refresh the children of item, reusing as much of the
+        existing items in the tree as possible. '''
+        existingChildren = self.GetItemChildren(item)
+        for childIndex in range(childrenCount):
+            childIndices = indices + [childIndex]
+            if childIndex < len(existingChildren):
+                child = existingChildren[childIndex]
+            else:
+                child = self.AppendItem(item, '')
+            self.RefreshRecursively(child, childIndices)
+        # Delete left-over items:
+        for existingChild in existingChildren[childrenCount:]:
+            self.Delete(existingChild)
+
+    def RefreshRecursively(self, item, indices):
+        childrenCount = self.OnGetChildrenCount(indices)
+        self.RefreshItem(item, indices, bool(childrenCount))
+        # We need to refresh the children when the item is expanded and
+        # when the item has no children, because in the latter case we
+        # might have to delete old children from the tree:
+        if self.IsExpanded(item) or not childrenCount:
+            self.RefreshChildrenRecursively(item, indices, childrenCount)
+        self.SetItemHasChildren(item, bool(childrenCount))
+            
+    def RefreshItem(self, item, indices, hasChildren):
+        ''' Refresh one item. '''
+        item = self.RefreshItemType(item, indices)
+        self.RefreshItemText(item, indices)
+        self.RefreshColumns(item, indices)
+        self.RefreshFont(item, indices)
+        self.RefreshTextColour(item, indices)
+        self.RefreshBackgroundColour(item, indices)
+        self.RefreshItemImage(item, indices, hasChildren)
+        self.RefreshCheckedState(item, indices)
+
+    def RefreshItemType(self, item, indices):
+        try:
+            currentType = self.GetItemType(item)
+        except AttributeError:
+            return item
+        type = self.OnGetItemType(indices)
+        if type != currentType:
+            # There's no way to change the type so we create a new item
+            # and delete the old one.
+            oldItem = item
+            item = self.InsertItem(self.GetItemParent(oldItem), item, '', 
+                ct_type=type)
+            self.Delete(oldItem)
+        return item
+
+    def RefreshItemText(self, item, indices):
+        itemText = self.OnGetItemText(indices)
+        if self.GetItemText(item) != itemText:
+            self.SetItemText(item, itemText)
+
+    def RefreshColumns(self, item, indices):
+        for columnIndex in range(1, self.GetColumnCount()):
+            itemText = self.OnGetItemText(indices, columnIndex)
+            if self.GetItemText(item, columnIndex) != itemText:
+                self.SetItemText(item, itemText, columnIndex)
+
+    def RefreshFont(self, item, indices):
+        font = self.OnGetItemFont(indices)
+        if self.GetItemFont(item) != font:
+            self.SetItemFont(item, font)
+
+    def RefreshTextColour(self, item, indices):
+        colour = self.OnGetItemTextColour(indices)
+        if self.GetItemTextColour(item) != colour:
+            self.SetItemTextColour(item, colour)
+
+    def RefreshBackgroundColour(self, item, indices):
+        # This one only seems to work for wx.TreeCtrl and not for
+        # wx.gizmos.TreeListCtrl and wx.lib.customtreectrl.CustomTreeCtrl...
+        colour = self.OnGetItemBackgroundColour(indices)
+        if self.GetItemBackgroundColour(item) != colour:
+            self.SetItemBackgroundColour(item, colour)
+
+    def RefreshItemImage(self, item, indices, hasChildren):
+        regularIcons = [wx.TreeItemIcon_Normal, wx.TreeItemIcon_Selected]
+        expandedIcons = [wx.TreeItemIcon_Expanded, 
+                         wx.TreeItemIcon_SelectedExpanded]
+        # Refresh images in first column:
+        for icon in regularIcons:
+            imageIndex = self.OnGetItemImage(indices, icon)
+            if self.GetItemImage(item, icon) != imageIndex:
+                self.SetItemImage(item, imageIndex, icon)
+        for icon in expandedIcons:
+            if hasChildren:
+                imageIndex = self.OnGetItemImage(indices, icon)
+            else:
+                imageIndex = -1
+            if self.GetItemImage(item, icon) != imageIndex or imageIndex == -1:
+                self.SetItemImage(item, imageIndex, icon)
+        # Refresh images in remaining columns, if any:
+        for columnIndex in range(1, self.GetColumnCount()):
+            for icon in regularIcons:
+                imageIndex = self.OnGetItemImage(indices, icon, columnIndex)
+                if self.GetItemImage(item, columnIndex, icon) != imageIndex:
+                    self.SetItemImage(item, imageIndex, icon, columnIndex)
+
+    def RefreshCheckedState(self, item, indices):
+        try: 
+            isChecked = self.IsItemChecked(item)
+        except AttributeError:
+            return # Checking not supported
+        shouldBeChecked = self.OnGetItemChecked(indices)
+        if isChecked != shouldBeChecked:
+            self.CheckItem(item, shouldBeChecked)
+
+    def OnItemExpanding(self, event):
+        indices = self.ItemIndices(event.GetItem())
+        childrenCount = self.OnGetChildrenCount(indices)
+        self.RefreshChildrenRecursively(event.GetItem(), indices, childrenCount)
+        event.Skip()
+
+    def OnItemCollapsed(self, event):
+        parent = self.GetItemParent(event.GetItem())
+        if not parent:
+            parent = self.GetRootItem()
+        indices = self.ItemIndices(parent)
+        childrenCount = self.OnGetChildrenCount(indices)
+        self.RefreshChildrenRecursively(parent, indices, childrenCount)
+        event.Skip()
+        
+    def ItemIndices(self, item):
+        ''' Construct index list for item. '''
+        parent = self.GetItemParent(item)
+        if parent:
+            parentIndices = self.ItemIndices(parent)
+            ownIndex = self.GetItemChildren(parent).index(item)
+            return parentIndices + [ownIndex]
+        else:
+            return []
+
+
+class DragAndDrop(TreeAPIHarmonizer):
+    ''' This is a mixin class that can be used to easily implement
+    dragging and dropping of tree items. It can be mixed in with 
+    wx.TreeCtrl, wx.gizmos.TreeListCtrl, or wx.lib.customtree.CustomTreeCtrl.
+
+    To use it derive a new class from this class and one of the tree
+    controls, e.g.:
+    class MyTree(DragAndDrop, wx.TreeCtrl):
+        ...
+
+    You *must* implement OnDrop. OnDrop is called when the user has
+    dropped an item on top of another item. It's up to you to decide how
+    to handle the drop. If you are using this mixin together with the
+    VirtualTree mixin, it makes sense to rearrange your underlying data
+    and then call RefreshItems to let de virtual tree refresh itself.
+    '''    
+ 
+    def __init__(self, *args, **kwargs):
+        kwargs['style'] = kwargs.get('style', wx.TR_DEFAULT_STYLE) | \
+                          wx.TR_HIDE_ROOT
+        super(DragAndDrop, self).__init__(*args, **kwargs)
+        self.Bind(wx.EVT_TREE_BEGIN_DRAG, self.OnBeginDrag)
+
+    def OnDrop(self, dropItem, dragItem):
+        ''' This function must be overloaded in the derived class.
+        dragItem is the item being dragged by the user. dropItem is the
+        item dragItem is dropped upon. If the user doesn't drop dragItem
+        on another item, dropItem equals the (hidden) root item of the
+        tree control. '''
+        raise NotImplementedError
+
+    def OnBeginDrag(self, event):
+        # We allow only one item to be dragged at a time, to keep it simple
+        self._dragItem = self.GetSelections()[0]
+        if self._dragItem: 
+            self.StartDragging()
+            event.Allow()
+        else:
+            event.Veto()
+
+    def OnEndDrag(self, event):
+        self.StopDragging()
+        dropTarget = event.GetItem()
+        if not dropTarget:
+            dropTarget = self.GetRootItem()
+        if self.IsValidDropTarget(dropTarget):
+            self.UnselectAll()
+            if dropTarget != self.GetRootItem():
+                self.SelectItem(dropTarget)
+            self.OnDrop(dropTarget, self._dragItem)
+
+    def OnDragging(self, event):
+        if not event.Dragging():
+            self.StopDragging()
+            return
+        item, flags, column = self.HitTest(wx.Point(event.GetX(), event.GetY()))
+        if not item:
+            item = self.GetRootItem()
+        if self.IsValidDropTarget(item):
+            self.SetCursorToDragging()
+        else:
+            self.SetCursorToDroppingImpossible()
+        if flags & wx.TREE_HITTEST_ONITEMBUTTON:
+            self.Expand(item)
+        selections = self.GetSelections()
+        if selections != [item]:
+            self.UnselectAll()
+            if item != self.GetRootItem():
+                self.SelectItem(item)
+        event.Skip()
+        
+    def StartDragging(self):
+        self.GetMainWindow().Bind(wx.EVT_MOTION, self.OnDragging)
+        self.Bind(wx.EVT_TREE_END_DRAG, self.OnEndDrag)
+        self.SetCursorToDragging()
+
+    def StopDragging(self):
+        self.GetMainWindow().Unbind(wx.EVT_MOTION)
+        self.Unbind(wx.EVT_TREE_END_DRAG)
+        self.ResetCursor()
+        self.UnselectAll()
+        self.SelectItem(self._dragItem)
+
+    def SetCursorToDragging(self):
+        self.GetMainWindow().SetCursor(wx.StockCursor(wx.CURSOR_HAND))
+        
+    def SetCursorToDroppingImpossible(self):
+        self.GetMainWindow().SetCursor(wx.StockCursor(wx.CURSOR_NO_ENTRY))
+        
+    def ResetCursor(self):
+        self.GetMainWindow().SetCursor(wx.NullCursor)
+
+    def IsValidDropTarget(self, dropTarget):
+        if dropTarget: 
+            allChildren = self.GetItemChildren(self._dragItem, recursively=True)
+            parent = self.GetItemParent(self._dragItem) 
+            return dropTarget not in [self._dragItem, parent] + allChildren
+        else:
+            return True        
+
+