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<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="howto-interface-implement"></a>How To define implement an Interface?</h2></div></div></div>
<p>
Once the interface is defined, implementing it is rather trivial. Source code showing how to do this
for the <span class="type">IBaz</span> interface defined in the previous section is located in
<code class="filename">sample/interface/maman-baz.{h|c}</code>.
</p>
<p>
The first step is to define a normal GType. Here, we have decided to use a GType which derives from
GObject. Its name is <span class="type">MamanBaz</span>:
</p>
<pre class="programlisting">
#ifndef MAMAN_BAZ_H
#define MAMAN_BAZ_H
#include <glib-object.h>
#define MAMAN_TYPE_BAZ (maman_baz_get_type ())
#define MAMAN_BAZ(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), MAMAN_TYPE_BAZ, Mamanbaz))
#define MAMAN_BAZ_CLASS(vtable) (G_TYPE_CHECK_CLASS_CAST ((vtable), MAMAN_TYPE_BAZ, MamanbazClass))
#define MAMAN_IS_BAZ(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_BAZ))
#define MAMAN_IS_BAZ_CLASS(vtable) (G_TYPE_CHECK_CLASS_TYPE ((vtable), MAMAN_TYPE_BAZ))
#define MAMAN_BAZ_GET_CLASS(inst) (G_TYPE_INSTANCE_GET_CLASS ((inst), MAMAN_TYPE_BAZ, MamanbazClass))
typedef struct _MamanBaz MamanBaz;
typedef struct _MamanBazClass MamanBazClass;
struct _MamanBaz {
GObject parent;
int instance_member;
};
struct _MamanBazClass {
GObjectClass parent;
};
GType maman_baz_get_type (void);
#endif //MAMAN_BAZ_H
</pre>
<p>
There is clearly nothing specifically weird or scary about this header: it does not define any weird API
or derives from a weird type.
</p>
<p>
The second step is to implement <code class="function">maman_baz_get_type</code>:
</p>
<pre class="programlisting">
GType
maman_baz_get_type (void)
{
static GType type = 0;
if (type == 0) {
static const GTypeInfo info = {
sizeof (MamanBazClass),
NULL, /* base_init */
NULL, /* base_finalize */
NULL, /* class_init */
NULL, /* class_finalize */
NULL, /* class_data */
sizeof (MamanBaz),
0, /* n_preallocs */
baz_instance_init /* instance_init */
};
static const GInterfaceInfo ibaz_info = {
(GInterfaceInitFunc) baz_interface_init, /* interface_init */
NULL, /* interface_finalize */
NULL /* interface_data */
};
type = g_type_register_static (G_TYPE_OBJECT,
"MamanBazType",
&info, 0);
g_type_add_interface_static (type,
MAMAN_TYPE_IBAZ,
&ibaz_info);
}
return type;
}
</pre>
<p>
This function is very much like all the similar functions we looked at previously. The only interface-specific
code present here is the call to <code class="function"><a href="gobject-Type-Information.html#g-type-add-interface-static">g_type_add_interface_static</a></code> which is used to inform
the type system that this just-registered <span class="type"><a href="gobject-Type-Information.html#GType">GType</a></span> also implements the interface
<code class="function">MAMAN_TYPE_IBAZ</code>.
</p>
<p>
<code class="function">baz_interface_init</code>, the interface initialization function, is also pretty simple:
</p>
<pre class="programlisting">
static void baz_do_action (MamanBaz *self)
{
g_print ("Baz implementation of IBaz interface Action: 0x%x.\n", self->instance_member);
}
static void
baz_interface_init (gpointer g_iface,
gpointer iface_data)
{
MamanIbazInteface *iface = (MamanIbazInteface *)g_iface;
iface->do_action = (void (*) (MamanIbaz *self))baz_do_action;
}
static void
baz_instance_init (GTypeInstance *instance,
gpointer g_class)
{
MamanBaz *self = MAMAN_BAZ(instance);
self->instance_member = 0xdeadbeaf;
}
</pre>
<p>
<code class="function">baz_interface_init</code> merely initializes the interface methods to the implementations
defined by <span class="type">MamanBaz</span>: <code class="function">maman_baz_do_action</code> does nothing very useful
but it could :)
</p>
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