Virtual table for handling properties and method calls for a D-Bus interface.

Since 2.38, if you want to handle getting/setting D-Bus properties asynchronously, give %NULL as your get_property() or set_property() function. The D-Bus call will be directed to your @method_call function, with the provided @interface_name set to "org.freedesktop.DBus.Properties".

Ownership of the #GDBusMethodInvocation object passed to the method_call() function is transferred to your handler; you must call one of the methods of #GDBusMethodInvocation to return a reply (possibly empty), or an error. These functions also take ownership of the passed-in invocation object, so unless the invocation object has otherwise been referenced, it will be then be freed. Calling one of these functions may be done within your method_call() implementation but it also can be done at a later point to handle the method asynchronously.

The usual checks on the validity of the calls is performed. For `Get` calls, an error is automatically returned if the property does not exist or the permissions do not allow access. The same checks are performed for `Set` calls, and the provided value is also checked for being the correct type.

For both `Get` and `Set` calls, the #GDBusMethodInvocation passed to the @method_call handler can be queried with g_dbus_method_invocation_get_property_info() to get a pointer to the #GDBusPropertyInfo of the property.

If you have readable properties specified in your interface info, you must ensure that you either provide a non-%NULL @get_property() function or provide implementations of both the `Get` and `GetAll` methods on org.freedesktop.DBus.Properties interface in your @method_call function. Note that the required return type of the `Get` call is `(v)`, not the type of the property. `GetAll` expects a return value of type `asv`.

If you have writable properties specified in your interface info, you must ensure that you either provide a non-%NULL @set_property() function or provide an implementation of the `Set` call. If implementing the call, you must return the value of type %G_VARIANT_TYPE_UNIT.