OOP Using GObject (9) – A Dynamic Type

Recall there are 3 types in GObject type system: Fundamental, static and dynamic. A fundamental type is a top-most type which has no parent type. Most of them are pre-defined. Static types never load/unload its class type (say, their class struct) at runtime, since they are static. On the contrary, dynamic types can be dynamically loaded/unloaded at runtime. They are normally used within a module.

We can call g_type_register_dynamic() to register a dynamic type. When used in a module of GObject library (may be a GTypeModule type), We can also call g_type_module_register_type() to create your dynamic types. g_type_register_dynamic() is invoked for you in that function. Let’s go through the code:

NOTE: PLEASE READ ALL COMMENT CAREFULLY.

The implementation structure may be a little different with the stuff when creating a static type. An additional parameter GTypeModule is passed in. It represents the module your dynamic type belongs to. So, when the module is unloaded, all dynamic types in it are unaccessible.

Also note the bar_type_class_finalize() function. We use it to override the finalize() virtual function in GObjectClass. Now you can do un-initialiation in this function. It is like the destructor in a C++ class.

Let’s move on to the module type. This type inherits GTypeModule:

GTypeModule is an abstract type. We should implements its load() and unload() virtual function.

Our test code:

Another dynamic type BarType is defined in addition to FooType to demo the usage. The output maybe:

See the init/finalize process?

At the end of my note, Let me summarize to compare GObject library with C++ implementation:

1. Member Variables:

GObject C++
in class struct class meta info
in object struct class instance member
global variable class static member

2. Function Callbacks:

GObject C++
base_init init class dynamic meta info
base_finalize finalize dynamic class meta info, only dynamic types use it
class_init init class static meta info
class_finalize finalize class static meta info, only dynamic types use it
instance_init init instace, like C++ constructor
override finalize in GObjectClass finalize instance, like C++ destructor

All source code is available in my skydrive: http://cid-481cbe104492a3af.office.live.com/browse.aspx/share/dev/TestOO. In the TestGObject-{date}.zip/TestGObject7 folder.

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