We made a very simple editor in the previous section with GtkTextView, GtkTextBuffer and GtkScrolledWindow. We will add file-reading ability to the program and improve it to a file viewer.
The easiest way to give a filename is to use a command line argument.
$ ./a.out filename
The program will open the file and insert its contents into the GtkTextBuffer.
To do this, we need to know how GtkApplication (or GApplication) recognizes arguments. This is described in the GIO API Reference – Application.
When GtkApplication is created, a flag (GApplicationFlags) is given as an argument.
*
GtkApplication (const gchar *application_id, GApplicationFlags flags); gtk_application_new
This tutorial explains only two flags,
G_APPLICATION_DEFAULT_FLAGS
and
G_APPLICATION_HANDLES_OPEN
.
(G_APPLICATION_FLAGS_NONE
was used instead of
G_APPLICATION_DEFAULT_FLAGS
before GIO version2.73.3 (GLib
2.73.3 5/Aug/2022). Some GTK 4 applications still use
G_APPLICATION_FLAGS_NONE
. But now it is deprecated and
G_APPLICATION_DEFAULT_FLAGS
is recommended.) If you want to
handle command line arguments, the
G_APPLICATION_HANDLES_COMMAND_LINE
flag is what you
need.
For further information, see GIO API Reference – ApplicationFlags and GIO API Reference – g_application_run.
We’ve already used G_APPLICATION_DEFAULT_FLAGS
, as it is
the simplest option, and no command line arguments are allowed. If you
give arguments, an error will occur.
The flag G_APPLICATION_HANDLES_OPEN
is the second
simplest option. It allows arguments but only files. The application
assumes all the arguments are filenames.
= gtk_application_new ("com.github.ToshioCP.tfv3", G_APPLICATION_HANDLES_OPEN); app
When G_APPLICATION_HANDLES_OPEN
flag is given to the
application, two signals are available.
The handler of the “open” signal is defined as follows.
void
(
open * self,
GApplication,
gpointer files,
gint n_files* hint,
gchar
gpointer user_data)
The parameters are:
self
— the application instance (usually
GtkApplication)files
— an array of GFiles. [array length=n_files]
[element-type GFile]n_files
— the number of the elements of
files
hint
— a hint provided by the calling instance (usually
it can be ignored)user_data
— user data set when the signal handler was
connected.A file viewer is a program that displays text files. Our file viewer will work as follows.
The program is shown below.
@@@include tfv/tfv3.c @@@
Save it as tfv3.c
. Then compile and run it.
$ comp tfv3
$ ./a.out tfv3.c
The function main
has only two changes from the previous
version.
G_APPLICATION_DEFAULT_FLAGS
is replaced by
G_APPLICATION_HANDLES_OPEN
g_signal_connect (app, "open", G_CALLBACK (app_open), NULL)
is added.When the flag G_APPLICATION_HANDLES_OPEN
is given to
gtk_application_new
function, the application behaves like
this:
The handler app_activate
becomes very simple. It just
outputs the error message and return to the caller. Then the application
quits immediately because no window is created.
The main work is done in the handler app_open
.
GTK_WRAP_WORD_CHAR
in
GtktextViewThe following is the file reading part of the program again.
if (g_file_load_contents (files[0], NULL, &contents, &length, NULL, NULL)) {
(tb, contents, length);
gtk_text_buffer_set_text (contents);
g_free if ((filename = g_file_get_basename (files[0])) != NULL) {
(GTK_WINDOW (win), filename);
gtk_window_set_title (filename);
g_free }
(win);
gtk_widget_show } else {
if ((filename = g_file_get_path (files[0])) != NULL) {
("No such file: %s.\n", filename);
g_printerr (filename);
g_free } else
("File can't be opened.\n");
g_printerr (GTK_WINDOW (win));
gtk_window_destroy }
The function g_file_load_contents
loads the file
contents into a temporary buffer, which is automatically allocated and
sets contents
to point the buffer. The length of the buffer
is assigned to length
. It returns TRUE
if the
file’s contents are successfully loaded or FALSE
if an
error occurs. If you want to know the details about
g_file_load_contents, see g file
load contents.
If it has successfully read the file, it inserts the contents into
GtkTextBuffer, frees the temporary buffer pointed by
contents
, sets the title of the window, frees the memories
pointed by filename
and then shows the window. If it fails,
it outputs an error message and destroys the window and finally make the
program quit.
GtkNotebook is a container widget that contains multiple widgets with tabs. It shows only one child at a time. Another child will be shown when its tab is clicked.
The left image is the window at the startup. The file
pr1.c
is shown and its filename is in the left tab. After
clicking on the right tab, the contents of the file tfv1.c
is shown. The right image is the screenshot.
The following is tfv4.c
. It has GtkNoteBook widget. It
is inserted as a child of GtkApplicationWindow and contains multiple
GtkScrolledWindow.
@@@include tfv/tfv4.c @@@
Most of the changes are in the function app_open
. The
numbers at the left of the following items are line numbers in the
source code.
nb
, lab
and
nbp
are defined. They point GtkNotebook, GtkLabel and
GtkNotebookPage respectively.files[i]
points i-th
GFile, which is created by the GtkApplication from the i-th command line
argument.contents
.filename
is freed..gtk_notebook_get_page
returns the GtkNotebookPage of the
child (GtkScrolledWindow).g_object_set
is a general function to set properties of
objects. See GObject API
Reference – g_object_set.filename
is
freed.filename
is NULL, the “No valid file is
given” message is displayed.