The function `tfe_text_view_new` generates a new TfeTextView instance.
@@@ tfe5/tfetextview.c tfe_text_view_new
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 file.)
- 11: Set the wrap mode of GtkTextView as GTK\_WRAP\_WORD\_CHAR.
- 12: Connect "changed" signal to a handler `on_changed`.
"changed" signal is defined in GtkTextBuffer.
It is emitted when the contents in the buffer is changed.
- 2-4: `on_changed` handler records TRUE to `tv->changed` when "changed" signal is emitted.
## Functions and Classes
In Gtk, all objects derived from GObject have class and instance.
Instance is memories which has a structure defined by C structure declaration as I mentioned in the previous two subsections.
And instance can be generated two or more.
Those instances have the same structure.
However, structured memories are insufficient to define its behavior.
We need at least two things.
One is functions and the other is class.
You've already seen many functions, for example, `tfe_text_view_new` is a function to generate TfeTextView instance.
These functions are similar to object methods in object oriented languages such as Java and Ruby.
Functions are public, which means that they are expected to be used by other objects.
Class comprises mainly pointers to functions.
And the functions are used by the object itself or its children objects.
For example, GObject class is declared in `gobject.h` in GLib source files.
@@@ class_gobject.c
I'd like to explain some of the members.
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. First is called disposing and the instance releases all the references to other instances. The second is finalizing.
- 23: A funtion pointed by `finalize` finishes the destruction process.
- The other pointers point functions which are called during 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.
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`.
@@@ tfe5/tfetextview.c 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.
