2b5f62a0b2
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18040 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
82 lines
4.9 KiB
TeX
82 lines
4.9 KiB
TeX
\section{wxTreeCtrl overview}\label{wxtreectrloverview}
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Classes: \helpref{wxTreeCtrl}{wxtreectrl}, \helpref{wxImageList}{wximagelist}
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The tree control displays its items in a tree like structure. Each item has its
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own (optional) icon and a label. An item may be either collapsed (meaning that
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its children are not visible) or expanded (meaning that its children are
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shown). Each item in the tree is identified by its {\it itemId} which is of
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opaque data type {\it wxTreeItemId}. You can test whether an item is valid
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by calling wxTreeItemId::IsOk.
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The items text and image may be retrieved and changed with
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\helpref{GetItemText}{wxtreectrlgetitemtext}/\helpref{SetItemText}{wxtreectrlsetitemtext}
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and
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\helpref{GetItemImage}{wxtreectrlgetitemimage}/\helpref{SetItemImage}{wxtreectrlsetitemimage}.
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In fact, an item may even have two images associated with it: the normal one
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and another one for selected state which is set/retrieved with
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\helpref{SetItemSelectedImage}{wxtreectrlsetitemselectedimage}/\helpref{GetItemSelectedImage}{wxtreectrlgetitemselectedimage}
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functions, but this functionality might be unavailable on some platforms.
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Tree items have several attributes: an item may be selected or not, visible or
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not, bold or not. It may also be expanded or collapsed. All these attributes
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may be retrieved with the corresponding functions:
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\helpref{IsSelected}{wxtreectrlisselected},
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\helpref{IsVisible}{wxtreectrlisvisible}, \helpref{IsBold}{wxtreectrlisbold}
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and \helpref{IsExpanded}{wxtreectrlisexpanded}. Only one item at a time may be
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selected, selecting another one (with
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\helpref{SelectItem}{wxtreectrlselectitem}) automatically unselects the
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previously selected one.
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In addition to its icon and label, a user-specific data structure may be associated
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with all tree items. If you wish to do it, you should derive a class from {\it
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wxTreeItemData} which is a very simple class having only one function {\it
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GetId()} which returns the id of the item this data is associated with. This
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data will be freed by the control itself when the associated item is deleted
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(all items are deleted when the control is destroyed), so you shouldn't delete
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it yourself (if you do it, you should call
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\helpref{SetItemData(NULL)}{wxtreectrlsetitemdata} to prevent the tree from
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deleting the pointer second time). The associated data may be retrieved with
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\helpref{GetItemData()}{wxtreectrlgetitemdata} function.
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Working with trees is relatively straightforward if all the items are added to
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the tree at the moment of its creation. However, for large trees it may be
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very inefficient. To improve the performance you may want to delay adding the
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items to the tree until the branch containing the items is expanded: so, in the
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beginning, only the root item is created (with
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\helpref{AddRoot}{wxtreectrladdroot}). Other items are added when
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EVT\_TREE\_ITEM\_EXPANDING event is received: then all items lying immediately
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under the item being expanded should be added, but, of course, only when this
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event is received for the first time for this item - otherwise, the items would
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be added twice if the user expands/collapses/re-expands the branch.
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The tree control provides functions for enumerating its items. There are 3
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groups of enumeration functions: for the children of a given item, for the
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sibling of the given item and for the visible items (those which are currently
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shown to the user: an item may be invisible either because its branch is
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collapsed or because it is scrolled out of view). Child enumeration functions
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require the caller to give them a {\it cookie} parameter: it is a number which
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is opaque to the caller but is used by the tree control itself to allow
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multiple enumerations to run simultaneously (this is explicitly allowed). The
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only thing to remember is that the {\it cookie} passed to
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\helpref{GetFirstChild}{wxtreectrlgetfirstchild} and to
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\helpref{GetNextChild}{wxtreectrlgetnextchild} should be the same variable (and
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that nothing should be done with it by the user code).
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Among other features of the tree control are: item sorting with
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\helpref{SortChildren}{wxtreectrlsortchildren} which uses the user-defined comparison
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function \helpref{OnCompareItems}{wxtreectrloncompareitems} (by default the
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comparison is the alphabetic comparison of tree labels), hit testing
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(determining to which portion of the control the given point belongs, useful
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for implementing drag-and-drop in the tree) with
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\helpref{HitTest}{wxtreectrlhittest} and editing of the tree item labels in
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place (see \helpref{EditLabel}{wxtreectrleditlabel}).
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Finally, the tree control has a keyboard interface: the cursor navigation (arrow) keys
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may be used to change the current selection. <HOME> and <END> are used to go to
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the first/last sibling of the current item. '+', '-' and '*' expand, collapse
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and toggle the current branch. Note, however, that <DEL> and <INS> keys do
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nothing by default, but it is usual to associate them with deleting item from
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a tree and inserting a new one into it.
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