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<H2><A NAME="sec_Tree_Widgets"></A> <A NAME="s12">12. Tree Widget </A></H2>
<P>The purpose of tree widgets is to display hierarchically-organized
data. The Tree widget itself is a vertical container for widgets of
type TreeItem. Tree itself is not terribly different from
CList - both are derived directly from Container, and the
Container methods work in the same way on Tree widgets as on
CList widgets. The difference is that Tree widgets can be nested
within other Tree widgets. We'll see how to do this shortly.
<P>The Tree widget has its own window, and defaults to a white
background, as does CList. Also, most of the Tree methods work in
the same way as the corresponding CList ones. However, Tree is
not derived from CList, so you cannot use them interchangeably.
<P>
<P>
<H2><A NAME="ss12.1">12.1 Creating a Tree</A>
</H2>
<P>A Tree is created in the usual way, using:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget *gtk_tree_new( void );
</PRE>
</CODE></BLOCKQUOTE>
<P>Like the CList widget, a Tree will simply keep growing as more
items are added to it, as well as when subtrees are expanded. For
this reason, they are almost always packed into a
ScrolledWindow. You might want to use gtk_widget_set_usize() on the
scrolled window to ensure that it is big enough to see the tree's
items, as the default size for ScrolledWindow is quite small.
<P>Now that you have a tree, you'll probably want to add some items to
it.
<A HREF="#sec_Tree_Item_Widget">The Tree Item Widget</A> below
explains the gory details of TreeItem. For now, it'll suffice to
create one, using:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget *gtk_tree_item_new_with_label( gchar *label );
</PRE>
</CODE></BLOCKQUOTE>
<P>You can then add it to the tree using one of the following (see
<A HREF="#sec_Tree_Functions">Functions and Macros</A>
below for more options):
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_append( GtkTree *tree,
GtkWidget *tree_item );
void gtk_tree_prepend( GtkTree *tree,
GtkWidget *tree_item );
</PRE>
</CODE></BLOCKQUOTE>
<P>Note that you must add items to a Tree one at a time - there is no
equivalent to gtk_list_*_items().
<P>
<H2><A NAME="ss12.2">12.2 Adding a Subtree</A>
</H2>
<P>A subtree is created like any other Tree widget. A subtree is added
to another tree beneath a tree item, using:
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_item_set_subtree( GtkTreeItem *tree_item,
GtkWidget *subtree );
</PRE>
</CODE></BLOCKQUOTE>
<P>You do not need to call gtk_widget_show() on a subtree before or after
adding it to a TreeItem. However, you <EM>must</EM> have added the
TreeItem in question to a parent tree before calling
gtk_tree_item_set_subtree(). This is because, technically, the parent
of the subtree is <EM>not</EM> the GtkTreeItem which "owns" it, but
rather the GtkTree which holds that GtkTreeItem.
<P>When you add a subtree to a TreeItem, a plus or minus sign appears
beside it, which the user can click on to "expand" or "collapse" it,
meaning, to show or hide its subtree. TreeItems are collapsed by
default. Note that when you collapse a TreeItem, any selected
items in its subtree remain selected, which may not be what the user
expects.
<P>
<H2><A NAME="ss12.3">12.3 Handling the Selection List</A>
</H2>
<P>As with CList, the Tree type has a <CODE>selection</CODE> field, and
it is possible to control the behaviour of the tree (somewhat) by
setting the selection type using:
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_set_selection_mode( GtkTree *tree,
GtkSelectionMode mode );
</PRE>
</CODE></BLOCKQUOTE>
<P>The semantics associated with the various selection modes are
described in the section on the CList widget. As with the CList
widget, the "select_child", "unselect_child" (not really - see
<A HREF="#sec_Tree_Signals">Signals</A> below for an explanation),
and "selection_changed" signals are emitted when list items are
selected or unselected. However, in order to take advantage of these
signals, you need to know <EM>which</EM> Tree widget they will be
emitted by, and where to find the list of selected items.
<P>This is a source of potential confusion. The best way to explain this
is that though all Tree widgets are created equal, some are more equal
than others. All Tree widgets have their own X window, and can
therefore receive events such as mouse clicks (if their TreeItems or
their children don't catch them first!). However, to make
<CODE>GTK_SELECTION_SINGLE</CODE> and <CODE>GTK_SELECTION_BROWSE</CODE> selection
types behave in a sane manner, the list of selected items is specific
to the topmost Tree widget in a hierarchy, known as the "root tree".
<P>Thus, accessing the <CODE>selection</CODE> field directly in an arbitrary
Tree widget is not a good idea unless you <EM>know</EM> it's the root
tree. Instead, use the <CODE>GTK_TREE_SELECTION (Tree)</CODE> macro, which
gives the root tree's selection list as a GList pointer. Of course,
this list can include items that are not in the subtree in question if
the selection type is <CODE>GTK_SELECTION_MULTIPLE</CODE>.
<P>Finally, the "select_child" (and "unselect_child", in theory) signals
are emitted by all trees, but the "selection_changed" signal is only
emitted by the root tree. Consequently, if you want to handle the
"select_child" signal for a tree and all its subtrees, you will have
to call gtk_signal_connect() for every subtree.
<P>
<H2><A NAME="ss12.4">12.4 Tree Widget Internals</A>
</H2>
<P>The Tree's struct definition looks like this:
<P>
<BLOCKQUOTE><CODE>
<PRE>
struct _GtkTree
{
GtkContainer container;
GList *children;
GtkTree* root_tree; /* owner of selection list */
GtkWidget* tree_owner;
GList *selection;
guint level;
guint indent_value;
guint current_indent;
guint selection_mode : 2;
guint view_mode : 1;
guint view_line : 1;
};
</PRE>
</CODE></BLOCKQUOTE>
<P>The perils associated with accessing the <CODE>selection</CODE> field
directly have already been mentioned. The other important fields of
the struct can also be accessed with handy macros or class functions.
<CODE>GTK_IS_ROOT_TREE (Tree)</CODE> returns a boolean value which
indicates whether a tree is the root tree in a Tree hierarchy, while
<CODE>GTK_TREE_ROOT_TREE (Tree)</CODE> returns the root tree, an object of
type GtkTree (so, remember to cast it using <CODE>GTK_WIDGET (Tree)</CODE> if
you want to use one of the gtk_widget_*() functions on it).
<P>Instead of directly accessing the children field of a Tree widget,
it's probably best to cast it using >tt/GTK_CONTAINER (Tree)/, and
pass it to the gtk_container_children() function. This creates a
duplicate of the original list, so it's advisable to free it up using
g_list_free() after you're done with it, or to iterate on it
destructively, like this:
<P>
<BLOCKQUOTE><CODE>
<PRE>
children = gtk_container_children (GTK_CONTAINER (tree));
while (children) {
do_something_nice (GTK_TREE_ITEM (children->data));
children = g_list_remove_link (children, children);
}
</PRE>
</CODE></BLOCKQUOTE>
<P>The <CODE>tree_owner</CODE> field is defined only in subtrees, where it
points to the TreeItem widget which holds the tree in question.
The <CODE>level</CODE> field indicates how deeply nested a particular tree
is; root trees have level 0, and each successive level of subtrees has
a level one greater than the parent level. This field is set only
after a Tree widget is actually mapped (i.e. drawn on the screen).
<P>
<H3><A NAME="sec_Tree_Signals"></A> Signals</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
void selection_changed( GtkTree *tree );
</PRE>
</CODE></BLOCKQUOTE>
<P>This signal will be emitted whenever the <CODE>selection</CODE> field of a
Tree has changed. This happens when a child of the Tree is
selected or deselected.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void select_child( GtkTree *tree,
GtkWidget *child );
</PRE>
</CODE></BLOCKQUOTE>
<P>This signal is emitted when a child of the Tree is about to get
selected. This happens on calls to gtk_tree_select_item(),
gtk_tree_select_child(), on <EM>all</EM> button presses and calls to
gtk_tree_item_toggle() and gtk_item_toggle(). It may sometimes be
indirectly triggered on other occasions where children get added to or
removed from the Tree.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void unselect_child (GtkTree *tree,
GtkWidget *child);
</PRE>
</CODE></BLOCKQUOTE>
<P>This signal is emitted when a child of the Tree is about to get
deselected. As of GTK 1.0.4, this seems to only occur on calls to
gtk_tree_unselect_item() or gtk_tree_unselect_child(), and perhaps on
other occasions, but <EM>not</EM> when a button press deselects a
child, nor on emission of the "toggle" signal by gtk_item_toggle().
<P>
<H3><A NAME="sec_Tree_Functions"></A> Functions and Macros</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
guint gtk_tree_get_type( void );
</PRE>
</CODE></BLOCKQUOTE>
<P>Returns the "GtkTree" type identifier.
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget* gtk_tree_new( void );
</PRE>
</CODE></BLOCKQUOTE>
<P>Create a new Tree object. The new widget is returned as a pointer to a
GtkWidget object. NULL is returned on failure.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_append( GtkTree *tree,
GtkWidget *tree_item );
</PRE>
</CODE></BLOCKQUOTE>
<P>Append a tree item to a Tree.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_prepend( GtkTree *tree,
GtkWidget *tree_item );
</PRE>
</CODE></BLOCKQUOTE>
<P>Prepend a tree item to a Tree.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_insert( GtkTree *tree,
GtkWidget *tree_item,
gint position );
</PRE>
</CODE></BLOCKQUOTE>
<P>Insert a tree item into a Tree at the position in the list
specified by <CODE>position.</CODE>
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_remove_items( GtkTree *tree,
GList *items );
</PRE>
</CODE></BLOCKQUOTE>
<P>Remove a list of items (in the form of a GList *) from a Tree.
Note that removing an item from a tree dereferences (and thus usually)
destroys it <EM>and</EM> its subtree, if it has one, <EM>and</EM> all
subtrees in that subtree. If you want to remove only one item, you
can use gtk_container_remove().
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_tree_clear_items( GtkTree *tree,
gint start,
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