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<div class="sect1" title="How To define implement an Interface?">
<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.
</p>
<p>
The first step is to define a normal GObject class, like:
</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_IS_BAZ(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_BAZ))
#define MAMAN_BAZ_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), MAMAN_TYPE_BAZ, MamanbazClass))
#define MAMAN_IS_BAZ_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), MAMAN_TYPE_BAZ))
#define MAMAN_BAZ_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), MAMAN_TYPE_BAZ, MamanbazClass))
typedef struct _MamanBaz MamanBaz;
typedef struct _MamanBazClass MamanBazClass;
struct _MamanBaz
{
GObject parent_instance;
int instance_member;
};
struct _MamanBazClass
{
GObjectClass parent_class;
};
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 <span class="type">MamanBaz</span> by defining
its GType. Instead of using <code class="function">G_DEFINE_TYPE</code> we
use <code class="function">G_DEFINE_TYPE_WITH_CODE</code> and the
<code class="function">G_IMPLEMENT_INTERFACE</code> macros.
</p>
<pre class="programlisting">
static void maman_ibaz_interface_init (MamanIbazInterface *iface);
G_DEFINE_TYPE_WITH_CODE (MamanBar, maman_bar, G_TYPE_OBJECT,
G_IMPLEMENT_INTERFACE (MAMAN_TYPE_IBAZ,
maman_ibaz_interface_init));
</pre>
<p>
This definition 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">G_IMPLEMENT_INTERFACE</code>.
</p>
<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>Classes can implement multiple interfaces by using multiple
calls to <code class="function">G_IMPLEMENT_INTERFACE</code> inside the call
to <code class="function">G_DEFINE_TYPE_WITH_CODE</code>.</p>
</div>
<p>
<code class="function">maman_baz_interface_init</code>, the interface
initialization function: inside it every virtual method of the interface
must be assigned to its implementation:
</p>
<pre class="programlisting">
static void
maman_baz_do_action (MamanBaz *self)
{
g_print ("Baz implementation of IBaz interface Action: 0x%x.\n",
self->instance_member);
}
static void
maman_ibaz_interface_init (MamanIbazInterface *iface)
{
iface->do_action = baz_do_action;
}
static void
maman_baz_init (MamanBaz *self)
{
MamanBaz *self = MAMAN_BAZ (instance);
self->instance_member = 0xdeadbeaf;
}
</pre>
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