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24 <a name="id535323"></a>Interface definition prerequisites</h2></div></div></div>
26 To specify that an interface requires the presence of other interfaces
27 when implemented, GObject introduces the concept of
28 <span class="emphasis"><em>prerequisites</em></span>: it is possible to associate
29 a list of prerequisite interfaces to an interface. For example, if
30 object A wishes to implement interface I1, and if interface I1 has a
31 prerequisite on interface I2, A has to implement both I1 and I2.
34 The mechanism described above is, in practice, very similar to
35 Java's interface I1 extends interface I2. The example below shows
36 the GObject equivalent:
38 <pre class="programlisting">
39 /* inside the GType function of the MamanIbar interface */
40 type = g_type_register_static (G_TYPE_INTERFACE, "MamanIbar", &info, 0);
42 /* Make the MamanIbar interface require MamanIbaz interface. */
43 g_type_interface_add_prerequisite (type, MAMAN_TYPE_IBAZ);
46 The code shown above adds the MamanIbaz interface to the list of
47 prerequisites of MamanIbar while the code below shows how an
48 implementation can implement both interfaces and register their
51 <pre class="programlisting">
53 maman_ibar_do_another_action (MamanIbar *ibar)
55 MamanBar *self = MAMAN_BAR (ibar);
57 g_print ("Bar implementation of IBar interface Another Action: 0x%x.\n",
58 self->instance_member);
62 maman_ibar_interface_init (MamanIbarInterface *iface)
64 iface->do_another_action = maman_ibar_do_another_action;
68 maman_ibaz_do_action (MamanIbaz *ibaz)
70 MamanBar *self = MAMAN_BAR (ibaz);
72 g_print ("Bar implementation of IBaz interface Action: 0x%x.\n",
73 self->instance_member);
77 maman_ibaz_interface_init (MamanIbazInterface *iface)
79 iface->do_action = maman_ibaz_do_action;
83 maman_bar_class_init (MamanBarClass *klass)
89 maman_bar_init (MamanBar *self)
91 self->instance_member = 0x666;
94 G_DEFINE_TYPE_WITH_CODE (MamanBar, maman_bar, G_TYPE_OBJECT,
95 G_IMPLEMENT_INTERFACE (MAMAN_TYPE_IBAZ,
96 maman_ibaz_interface_init)
97 G_IMPLEMENT_INTERFACE (MAMAN_TYPE_IBAR,
98 maman_ibar_interface_init));
101 It is very important to notice that the order in which interface
102 implementations are added to the main object is not random:
103 <code class="function"><a class="link" href="gobject-Type-Information.html#g-type-add-interface-static" title="g_type_add_interface_static ()">g_type_add_interface_static</a></code>,
104 which is called by <code class="function">G_IMPLEMENT_INTERFACE</code>, must be
105 invoked first on the interfaces which have no prerequisites and then on
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