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class Fl_Group

Class Hierarchy

Include Files

    #include <FL/Fl_Group.H>


The Fl_Group class is the FLTK container widget. It maintains an array of child widgets. These children can themselves be any widget including Fl_Group. The most important subclass of Fl_Group is Fl_Window, however groups can also be used to control radio buttons or to enforce resize behavior.


Fl_Group::Fl_Group(int x, int y, int w, int h, const char *label = 0)

Creates a new Fl_Group widget using the given position, size, and label string. The default boxtype is FL_NO_BOX.

virtual Fl_Group::~Fl_Group()

The destructor also deletes all the children. This allows a whole tree to be deleted at once, without having to keep a pointer to all the children in the user code. A kludge has been done so the Fl_Group and all of it's children can be automatic (local) variables, but you must declare the Fl_Group first, so that it is destroyed last.

void Fl_Group::add(Fl_Widget &w)
void Fl_Group::add(Fl_Widget *w)

The widget is removed from it's current group (if any) and then added to the end of this group.

void Fl_Group::clear()

The clear() method deletes all child widgets from memory recursively.

This method differs from the remove() method in that it affects all child widgets and deletes them from memory.

void Fl_Group::clip_children(int c);
int Fl_Group::clip_children();

The first method controls whether the group widget clips the drawing of child widgets to its bounding box.

The second method returns the current clipping mode.

The default is to not clip (0) the drawing of child widgets.

void Fl_Group::init_sizes()

The Fl_Group widget keeps track of the original widget sizes and positions when resizing occurs so that if you resize a window back to its original size the widgets will be in the correct places. If you rearrange the widgets in your group, call this method to register the new arrangement with the Fl_Group that contains them.

void Fl_Group::insert(Fl_Widget &w, int n)

The widget is removed from it's current group (if any) and then inserted into this group. It is put at index n (or at the end if n >= children(). This can also be used to rearrange the widgets inside a group.

void Fl_Group::insert(Fl_Widget &w, Fl_Widget* beforethis)

This does insert(w, find(beforethis)). This will append the widget if beforethis is not in the group.

void Fl_Group::remove(Fl_Widget &w)

Removes a widget from the group but does not delete it. This method does nothing if the widget is not a child of the group.

This method differs from the clear() method in that it only affects a single widget and does not delete it from memory.

static Fl_Group *Fl_Group::current()
static void Fl_Group::current(Fl_Group *w)

current() returns the currently active group. The Fl_Widget constructor automatically does current()->add(widget) if this is not null. To prevent new widgets from being added to a group, call Fl_Group::current(0).

void Fl_Group::begin()

begin() sets the current group so you can build the widget tree by just constructing the widgets. begin() is automatically called by the constructor for Fl_Group (and thus for Fl_Window as well). begin() is exactly the same as current(this).

Don't forget to end() the group or window!

void Fl_Group::end()

end() is exactly the same as current(this->parent()). Any new widgets added to the widget tree will be added to the parent of the group.

const Fl_Widget **Fl_Group::array() const

Returns a pointer to the array of children. This pointer is only valid until the next time a child is added or removed.

Fl_Widget *Fl_Group::child(int n) const

Returns array()[n]. No range checking is done!

int Fl_Group::children() const

Returns how many child widgets the group has.

int Fl_Group::find(const Fl_Widget *w) const
int Fl_Group::find(const Fl_Widget &w) const

Searches the child array for the widget and returns the index. Returns children() if the widget is NULL or not found.

void Fl_Group::resizable(Fl_Widget *box)
void Fl_Group::resizable(Fl_Widget &box)
Fl_Widget *Fl_Group::resizable() const

The resizable widget defines the resizing box for the group. When the group is resized it calculates a new size and position for all of its children. Widgets that are horizontally or vertically inside the dimensions of the box are scaled to the new size. Widgets outside the box are moved.

In these examples the gray area is the resizable:

Resizeable groups   Resizeable groups

The resizable may be set to the group itself (this is the default value for an Fl_Group, although NULL is the default for Fl_Window and Fl_Pack), in which case all the contents are resized. If the resizable is NULL then all widgets remain a fixed size and distance from the top-left corner.

It is possible to achieve any type of resize behavior by using an invisible Fl_Box as the resizable and/or by using a hierarchy of child Fl_Group's.

Fl_Group &Fl_Group::add_resizable(Fl_Widget &box)

Adds a widget to the group and makes it the resizable widget.

User Comments [ Add Comment ]

From Nathan Black, 19:04 Mar 11, 2004 (score=1)

You must call this AFTER you add all your UI elements, or it will cause the controls not to respond for controls added later.
Reply ]

From greg.ercolano, 10:02 Nov 23, 2006 (score=3)

I think Nathan is referring to calling the init_sizes() method here.
Reply ]


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