Functions in GtkNotebook

GtkNotebook is a very important object in the text file editor tfe. It connects the application and TfeTextView objects. A set of public functions are declared in tfenotebook.h. The word “tfenotebook” is used only in filenames. There’s no “TfeNotebook” object.

@@@include tfe5/tfenotebook.h @@@

This header file describes the public functions in tfenotebook.c.

• 1-2: notebook_page_save saves the current page to the file of which the name specified in the tab. If the name is untitled or untitled followed by digits, FileChooserDialog appears and a user can choose or specify a filename.
• 4-5: notebook_page_close closes the current page.
• 7-8: notebook_page_open shows a file chooser dialog and a user can choose a file. The file is inserted to a new page.
• 10-11: notebook_page_new_with_file creates a new page and a file given as an argument is read and inserted into the page.
• 13-14: notebook_page_new creates a new empty page.

You probably find that the functions except notebook_page_close are higher level functions of

• tfe_text_view_save
• tef_text_view_open
• tfe_text_view_new_with_file
• tfe_text_view_new

respectively.

There are two layers. One of them is tfe_text_view ..., which is the lower level layer. The other is note_book ..., which is the higher level layer.

Now let’s look at the program of each function.

notebook_page_new

@@@include tfe5/tfenotebook.c get_untitled notebook_page_build notebook_page_new @@@

• 26-38: notebook_page_new function.
• 28: g_return_if_fail is used to check the argument.
• 33-34: Creates TfeTextView object. If it fails, no notebook page is created and the function returns to the caller.
• 35: Creates filename, which is “Untitled”, “Untitled1”, … .
• 1-8: get_untitled function.
• 3: Static variable c is initialized at the first call of this function. After that c keeps its value unless it is changed explicitly.
• 4-7: Increases c by one and if it is zero, it returns “Untitled”. If it is a positive integer, it returns “Untitled<the integer>”, for example, “Untitled1”, “Untitled2”, and so on. The function g_strdup_printf creates a string and it should be freed by g_free when it becomes useless. The caller of get_untitled is in charge of freeing the string.
• 36: calls notebook_page_build to build the contents of the page.
• 37: frees filename.
• 10- 24: notebook_page_build function. A parameter with const qualifier doesn’t change in the function. It means that the argument filename is owned by the caller. The caller needs to free it when it becomes useless.
• 12: Creates GtkScrolledWindow.
• 17: Inserts tv to GtkscrolledWindow as a child.
• 18-19: Creates GtkLabel, then appends scr and lab to the GtkNotebook instance nb.
• 20-21: Sets “tab-expand” property to TRUE. The function g_object_set sets properties on an object. The object is any object derived from GObject. In many cases, an object has its own function to set its properties, but sometimes not. In that case, use g_object_set to set the property.
• 22: Sets the current page to the newly created page.
• 23: Connects “change-file” signal and file_changed_cb handler.

notebook_page_new_with_file

@@@include tfe5/tfenotebook.c notebook_page_new_with_file @@@

• 9-10: Calls tfe_text_view_new_with_file. If the function returns NULL, an error has happend. Then, it does nothing and returns.
• 11-13: Gets the filename, builds the contents of the page and frees filename.

notebook_page_open

@@@include tfe5/tfenotebook.c open_response notebook_page_open @@@

• 18-28: notebook_page_open function.
• 24-25: Creates TfeTextView object. If NULL is returned, an error has happened. Then, it returns to the caller.
• 26: Connects the signal “open-response” and the handler open_response.
• 27: Calls tfe_text_view_open. The “open-response” signal will be emitted later to inform the result of opening and reading a file.
• 1-16: open_response handler.
• 6-8: If the response code is not TFE_OPEN_RESPONSE_SUCCESS, it has failed to open and read a new file. Then, what notebook_page_open did in advance need to be canceled. The instance tv hasn’t been a child widget of GtkScrolledWindow yet. Such instance has floating reference. Floating reference will be explained later. You need to call g_object_ref_sink first. Then the floating reference is converted into an ordinary reference. Now you call g_object_unref to decrease the reference count by one.
• 9-15: Otherwise, everything is okay. Gets the filename, builds the contents of the page and frees filename.

Floating reference

All the widgets are derived from GInitiallyUnowned. GObject and GInitiallyUnowned are almost the same. The difference is like this. When an instance of GInitiallyUnowned is created, the instance has a floating reference and its reference count is zero. On the other hand, when an instance of GObject (not GInitiallyUnowned) is created, no floating reference is given. And the instance has a normal reference count instead of floating reference. Their descendants inherits them, so every widget has a floating reference at first. Non-widget class, for example, GtkTextBuffer is a direct sub class of GObject and it doesn’t have floating reference. Its reference count is one when it is created.

The function g_object_ref_sink converts the floating reference into an ordinary reference. If the instance doesn’t have a floating reference, g_object_ref_sink simply increases the reference count by one. It is used when an widget is added to another widget as a child.

GtkTextView *tv = gtk_text_view_new (); // floating reference
GtkScrolledWindow *scr = gtk_scrolled_window_new ();
gtk_scrolled_window_set_child (scr, tv); // tv's reference count is one

When tv is added to scr as a child, g_object_ref_sink is used.

g_object_ref_sink (tv);

So, the floating reference is converted into an ordinary reference. That is to say, floating reference is deleted, and reference count turns to one. Thanks to this, the caller doesn’t need to decrease tv’s reference count. If an Object_A is not a descendant of GInitiallyUnowned, the program is like this:

Object_A *obj_a = object_a_new (); // reference count is one
GtkScrolledWindow *scr = gtk_scrolled_window_new ();
gtk_scrolled_window_set_child (scr, obj_a); // obj_a's reference count is two
// obj_a is referred by the caller (this program) and scrolled window
g_object_unref (obj_a); // obj_a's reference count is one because the caller no longer refers obj_a.

This example tells us that the caller needs to unref obj_a.

If you use g_object_unref to an instance that has a floating reference, you need to convert the floating reference to a normal reference in advance. See GObject API reference for further information.

notebook_page_close

@@@include tfe5/tfenotebook.c notebook_page_close @@@

This function closes the current page. If the page is the only page the notebook has, then the function destroys the top-level window and quits the application.

• 8-10: If the page is the only page the notebook has, it calls gtk_window_destroy to destroys the top-level window.
• 11-13: Otherwise, removes the current page. The child widget (TfeTextView) is also destroyed.

notebook_page_save

@@@include tfe5/tfenotebook.c get_current_textview notebook_page_save @@@

• 13-21: notebook_page_save.
• 19: Gets TfeTextView belongs to the current page.
• 20: Calls tfe_text_view_save.
• 1-11: get_current_textview. This function gets the TfeTextView object belongs to the current page.
• 7: Gets the page number of the current page.
• 8: Gets the child widget scr, which is a GtkScrolledWindow instance, of the current page.
• 9-10: Gets the child widget of scr, which is a TfeTextView instance, and returns it.

file_changed_cb handler

The function file_changed_cb is a handler connected to “change-file” signal. If a file in a TfeTextView instance is changed, it emits this signal. This handler changes the label of the GtkNotebookPage.

@@@include tfe5/tfenotebook.c file_changed_cb @@@

• 8: Gets the GFile instance from tv.
• 9: Gets the GkScrolledWindow instance which is the parent widget of tv.
• 10-12: If file points GFile, then assigns the filename of the GFile into filename. Then, unref the GFile object file.
• 13-14: Otherwise (file is NULL), assigns untitled string to filename.
• 15-16: Creates a GtkLabel instance label with the filename and set the label of the GtkNotebookPage with label.