TreeCtrl Overview¶The tree control displays its items in a tree like structure. Each
item has its own (optional) icon and a label. An item may be either
collapsed (meaning that its children are not visible) or expanded
(meaning that its children are shown). Each item in the tree is
identified by its itemId which is of opaque data type
wx.TreeItemId. You can test whether an item is valid by calling
wx.TreeItemId.IsOk.
The items text and image may be retrieved and changed with (Get|Set)ItemText and (Get|Set)ItemImage. In fact, an item may even have two images associated with it: the normal one and another one for selected state which is set/retrieved with (Get|Set)ItemSelectedImage functions, but this functionality might be unavailable on some platforms.
Tree items have several attributes: an item may be selected or not,
visible or not, bold or not. It may also be expanded or collapsed. All
these attributes may be retrieved with the corresponding functions:
wx.TreeCtrl.IsSelected, wx.TreeCtrl.IsVisible,
wx.TreeCtrl.IsBold and wx.TreeCtrl.IsExpanded. Only
one item at a time may be selected, selecting another one (with
wx.TreeCtrl.SelectItem) automatically unselects the previously
selected one.
In addition to its icon and label, a user-specific data structure may
be associated with all tree items. If you wish to do it, you should
derive a class from wx.TreeItemData which is a very simple
class having only one function GetId() which returns the id of the
item this data is associated with. This data will be freed by the
control itself when the associated item is deleted (all items are
deleted when the control is destroyed), so you shouldn’t delete it
yourself (if you do it, you should call SetItemData(None) to prevent
the tree from deleting the pointer second time). The associated data
may be retrieved with wx.TreeCtrl.GetItemData function.
Working with trees is relatively straightforward if all the items are
added to the tree at the moment of its creation. However, for large
trees it may be very inefficient. To improve the performance you may
want to delay adding the items to the tree until the branch containing
the items is expanded: so, in the beginning, only the root item is
created (with wx.TreeCtrl.AddRoot). Other items are added when
wx.EVT_TREE_ITEM_EXPANDING event is received: then all items lying
immediately under the item being expanded should be added, but, of
course, only when this event is received for the first time for this
item - otherwise, the items would be added twice if the user
expands/collapses/re-expands the branch.
The tree control provides functions for enumerating its items. There
are 3 groups of enumeration functions: for the children of a given
item, for the sibling of the given item and for the visible items
(those which are currently shown to the user: an item may be invisible
either because its branch is collapsed or because it is scrolled out
of view). Child enumeration functions require the caller to give them
a cookie parameter: it is a number which is opaque to the caller but
is used by the tree control itself to allow multiple enumerations to
run simultaneously (this is explicitly allowed). The only thing to
remember is that the cookie passed to
wx.TreeCtrl.GetFirstChild and to
wx.TreeCtrl.GetNextChild should be the same variable (and that
nothing should be done with it by the user code).
Among other features of the tree control are:
Item Sorting with wx.TreeCtrl.SortChildren which uses the
user-defined comparison function OnCompareItems (by default the
comparison is the alphabetic comparison of tree labels);
Hit Testing (determining to which portion of the control the given
point belongs, useful for implementing drag-and-drop in the tree)
with wx.TreeCtrl.HitTest;
Editing of the tree item labels in place (see
wx.TreeCtrl.EditLabel).
Finally, the tree control has a keyboard interface: the cursor
navigation (arrow) keys may be used to change the current
selection. HOME and END are used to go to the first/last
sibling of the current item. +, - and * expand, collapse
and toggle the current branch. Note, however, that DEL and INS
keys do nothing by default, but it is common to associate them with
deleting an item from a tree and inserting a new one into it.
See also
