When this function is run, the following procedure is gone through.
1. Initialize GObject instance in TfeTextView instance.
2. Initialize GtkWidget instance in TfeTextView instance.
3. Initialize GtkTextView instance in TfeTextView instance.
4. Initialize TfeTextView instance.
Step one through three is done automatically.
Step four is done by the function `tfe_text_view_init`.
> In the same way, `gtk_text_view_init`, `gtk_widget_init` and `g_object_init` is the initialization functions of GtkTextView, GtkWidget and GObject respectively.
> You can find them in the GTK or GLib source files.
There's a pointer to the function `dispose` in line 22.
void (*dispose) (GObject *object);
The declaration is a bit complicated.
The asterisk before the identifier `dispose` means pointer.
So, the pointer `disopse` points a function which has one parameter , which points a GObject structure, and returns no value because of void type.
In the same way, line 23 says `finalize` is a pointer to the function which has one paremeter, which points a GObject structure, and returns no value.
void (*finalize) (GObject *object);
Look at the declaration of `_GObjectClass` so that you would find that most of the members are pointers to functions.
- 10: A function pointed by `constructor` is called when the instance is generated. It completes the initialization of the instance.
- 22: A function pointed by `dispose` is called when the instance destructs itself. Destruction process is divided into two phases. The first one is called disposing and the instance releases all the references to other instances. The second one is finalizing.
- 23: A funtion pointed by `finalize` finishes the destruction process.
- The other pointers point functions which are called while the instance lives.
## TfeTextView class
TfeTextView class is a structure and it includes all its ancestors' class in it.
Let's look at all the classes from GObject, which is the top level object, to TfeTextView object, which is the lowest.
104 /* The following definition is generated by the macro G_DECLARE_FINAL_TYPE
105 typedef struct {
106 GtkTextView parent_class;
107 } TfeTextViewClass;
108
- 105-107: This three lines are generated by the macro G\_DECLARE\_FINAL\_TYPE.
So, they are not written in either `tfe_text_view.h` or `tfe_text_view.c`.
- 2, 73, 106: Each derived class puts its parent class at the first member of its structure.
It is the same as instance structures.
- Class members in ancesters are open to the descendent class.
So, they can be changed in `tfe_text_view_class_init` function.
For example, the `dispose` pointer in GObjectClass will be overridden later in `tfe_text_view_class_init`.
(Override is an object oriented programing terminology.
Override is rewriting ancestors' class methods in the descendent class.)
- Some class methods are often overridden.
`set_property`, `get_property`, `dispose`, `finalize` and `constructed` are such methods.
TfeTextViewClass includes its ancsestors' class in it.
It is illustrated in the following diagram.
## Destruction of TfeTextView
Every Object derived from GObject has a reference count.
If an object A uses an object B, then A keeps a pointr to B in A and at the same time increaces the reference count of B by one with the function `g_object_ref (B)`.
If A doesn't need B any longer, then A discards the pointer to B (usually it is done by assigning NULL to the pointer) and decreaces the reference count of B by one with the function `g_object_unref (B)`.
If two objects A and B refer to C, then the reference count of C is two.
After A used C and if A no longer needs C, A discards the pointer to C and decreases the reference count in C by one.
Now the reference count of C is one.
In the same way, when B no longer needs C, B discards the pointer to C and decreases the reference count in C by one.
At this moment, no object refers C and the reference count of C is zero.
This means C is no longer useful.
Then C destructs itself and finally the memories allocated to C is freed.
The idea above is based on an assumption that an object refered by nothing has reference count of zero.
When the reference count drops to zero, the object starts its destruction process.
The destruction process is split in two phases: disposing and finalizing.
In the disposing process, the object invokes the handler pointed by `dispose` in its class to release all references to other objects.
In the finalizing process, it invokes the handler pointed by `finalize` in its class to complete the destruction process.
In the destruction process of TfeTextView, the reference count of widgets related to TfeTextView is automatically decreased.
But GFile pointed by `tv->file` needs to decrease its reference count by one.
You must write the code in the dispose handler `tfe_text_view_dispose`.
- 5,6: If `tv->file` points a GFile, decrease its reference count.
`g_clear_object` decreases the reference count and assigns NULL to `tv->file`. In dispose handlers, we usually use `g_clear_object` rather than `g_object_unref`.
- 8: invoke parent's despose handler. (This will be explained later.)
In the desposing process, the object uses the pointer in its class to call the handler.
Therefore, `tfe_text_view_dispose` needs to be registerd in the class when the TfeTextView class is initialized.
The function `tfe_text_view_class_init` is the class initialization function and it is declared in the replacement produced by `G_DEFINE_TYPE` macro.
