GtkAda Reference Manual - Package Gtk.Object

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# Package Gtk.Object

This is the base class of the widget hierarchy. Everything in GtkAda inherits from this class Gtk_Object, except for a few structures in the Gdk.* packages (low-level drawing routines).

This class provides a set of handful features that you can choose to reuse in your applications:

- Reference counting: an object is not deleted while there exists at least one reference to it. Although GtkAda mostly takes care of that aspect transparently, you might need in some obscure cases to increment or decrement the reference counting for a widget manually, so that it is not removed from memory while you still need it.
- User data: any number of data can be attached to a Gtk_Object or one of its children. Theses data are referenced by a String, in a hash-table. GtkAda itself uses this feature to provide an easy conversion between C and Ada widgets. Although you might prefer to have a completely object-oriented application (and thus associate data through class inheritance), it might be convenient to directly attach some data to your objects.
- It also contains the basic structures and subprograms required for signal emission. This is of course used to implement the signal mechanism in GtkAda itself, but can also be used to implement a Model/View/Controller framework.

Note that a lot of functions provided in the C interface are not provided here. They are used to emulate an object-oriented language in C, which can of course be done much more conveniently in Ada. Therefore most of these functions are not needed.

Here is a brief explanation on how the reference counting and destruction process work. You should not have to understand all this to use GtkAda, but it might help anyway.

When an object (descendant of Gtk.Object) is created, it has initially a ref_count of 1. A flag is set to say the object is "floating". See the Flags functions in this package for how to retrieve the status of this flag.

When the object gets a parent (ie Gtk.Widget.Set_Parent is called, possibly from other subprograms like Gtk.Container.Add, Gtk.Box.Pack_Start, ...), the ref_count of the object is incremented to 2. If the object was still "floating", it is also "sinked", ie its ref_count is decremented to 1, and the "floating" flag is cleared.

The same behavior as above happens when the object is registered as a top-level widget (i.e. we know it won't have any parent).

Thus the normal life cycle of an object is to have a ref_count to 1, and not be a "floating" object.

When the object is destroyed, the following happens: A temporary reference to the object is created (call to Ref), and ref_count to 2. The object is shutdown: It is removed from its parent (if any), and its ref_count is decremented to 1. The "destroy" signal is emitted, the user's handlers are called, and then all the handlers connected to the object are destroyed. The object is unref-ed. If its ref_count goes down to 0 (normal case), the memory used by the object and its user_data is freed.

- Gtk.Object Widget Hierarchy
- Gtk.Object Signals
- Gtk.Object Subprograms

## Widget Hierarchy

    GObject                       (see section Package Glib.Object)
    Gtk_Object                    (see section Package Gtk.Object)

## Signals

- "destroy" procedure Handler (Object : access Gtk_Object_Record'Class);
  Raised when the object is about to be destroyed. The "destroyed" flag has been set on the object first. Handlers should not keep a reference on the object. Note that when your destroy handlers are called, the user_data is still available. The default implementation destroys all the handlers.

## Subprograms

    procedure Sink
      (Object             : access Gtk_Object_Record);
| Sink the object. If the object is floating (does not have a parent yet), it is unref-ed once and the floating flag is cleared.
    procedure Destroy
      (Object             : access Gtk_Object_Record);
| Destroy the object. This emits a "destroy" signal, calls all your handlers, and then unconnects them all. The object is then unref-ed, and if its reference count goes down to 0, the memory associated with the object and its user data is freed. Note that when you destroy handlers are called, the user_data is still available.
    function Get_Type              return Gtk.Gtk_Type;
| Return the internal value associated with a Gtk_Object internally.
    function Get_Type
      (Object             : access Gtk_Object_Record)
       return Gtk_Type;
| This function is now obsolete, and is temporarily kept for backward compatibility only. Use Glib.Object.Get_Type instead. ???
### Flags
Each object is associated with a set of flags, that reports the state of the object. The following flags are known by all objects: "Destroyed": Set if the object is marked as destroyed (if its reference count is not yet 0, the memory has not been freed, but you should not use it anyway). "Floating": The object has no parent yet, since it was just created. Its reference count is still 1 (as it was initially). This flag is cleared as soon as Set_Parent is called on the widget or the widget is qualified as a toplevel widget (see Gtk.Container.Register_Toplevel).
    function Flags
      (Object             : access Gtk_Object_Record)
       return Guint32;
| Return the flags that are set for the object, as a binary mask.
    procedure Set_Flags
      (Object             : access Gtk_Object_Record;
       Flags              :        Guint32);
| Set some specific flags for the object. Flags is a mask that will be added to the current flags of the object.
    procedure Unset_Flags
      (Object             : access Gtk_Object_Record;
       Flags              :        Guint32);
| Unset some specific flags for the object. Flags is a mask that will be deleted from the current flags of the object.
    function Flag_Is_Set
      (Object             : access Gtk_Object_Record;
       Flag               :        Guint32)
       return Boolean;
| Return True if the specific flag Flag is set for the object.
    function In_Destruction_Is_Set
      (Object             : access Gtk_Object_Record'Class)
       return Boolean;
| Test if the Destroyed flag is set for the object.
    function Floating_Is_Set
      (Object             : access Gtk_Object_Record'Class)
       return Boolean;
| Test if the Floating flag is set for the object.

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