Gtk4-tutorial/gfm/sec12.md

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Functions in TfeTextView

In this section I will explain functions in TfeTextView object.

tfe.h and tfetextview.h

tfe.h is a top header file and it includes gtk.h and all the header files. C source files tfeapplication.c and tfenotebook.c include tfe.h at the beginning.

1 #include <gtk/gtk.h>
2 
3 #include "../tfetextview/tfetextview.h"
4 #include "tfenotebook.h"

../tfetextview/tfetextview.h is a header file which describes the public functions in tfetextview.c.

 1 #ifndef __TFE_TEXT_VIEW_H__
 2 #define __TFE_TEXT_VIEW_H__
 3 
 4 #include <gtk/gtk.h>
 5 
 6 #define TFE_TYPE_TEXT_VIEW tfe_text_view_get_type ()
 7 G_DECLARE_FINAL_TYPE (TfeTextView, tfe_text_view, TFE, TEXT_VIEW, GtkTextView)
 8 
 9 /* "open-response" signal response */
10 enum TfeTextViewOpenResponseType
11 {
12   TFE_OPEN_RESPONSE_SUCCESS,
13   TFE_OPEN_RESPONSE_CANCEL,
14   TFE_OPEN_RESPONSE_ERROR
15 };
16 
17 GFile *
18 tfe_text_view_get_file (TfeTextView *tv);
19 
20 void
21 tfe_text_view_open (TfeTextView *tv, GtkWindow *win);
22 
23 void
24 tfe_text_view_save (TfeTextView *tv);
25 
26 void
27 tfe_text_view_saveas (TfeTextView *tv);
28 
29 GtkWidget *
30 tfe_text_view_new_with_file (GFile *file);
31 
32 GtkWidget *
33 tfe_text_view_new (void);
34 
35 #endif /* __TFE_TEXT_VIEW_H__ */

• 1,2,35: Thanks to these three lines, the following lines are included only once.
• 4: Includes gtk4 header files. The header file gtk4 also has the same mechanism to avoid including it multiple times.
• 6-7: These two lines define TfeTextView type, its class structure and some useful macros.
• 9-15: A definition of the value of the parameter of "open-response" signal.
• 17-33: Declarations of public functions on TfeTextView.

Functions to create TfeTextView object

TfeTextView Object is created with tfe_text_view_new or tfe_text_view_new_with_file.

GtkWidget *tfe_text_view_new (void);

tfe_text_view_new just creates a new TfeTextView object and returns the pointer to the new object.

GtkWidget *tfe_text_view_new_with_file (GFile *file);

tfe_text_view_new_with_file is given a Gfile object as the argument and it loads the file into the GtkTextBuffer object, then returns the pointer to the new object. If an error occurs during the creation process, NULL is returned.

Each function is defined as follows.

 1 GtkWidget *
 2 tfe_text_view_new_with_file (GFile *file) {
 3   g_return_val_if_fail (G_IS_FILE (file), NULL);
 4 
 5   GtkWidget *tv;
 6   GtkTextBuffer *tb;
 7   char *contents;
 8   gsize length;
 9 
10   if (! g_file_load_contents (file, NULL, &contents, &length, NULL, NULL)) /* read error */
11     return NULL;
12 
13   tv = tfe_text_view_new();
14   tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
15   gtk_text_buffer_set_text (tb, contents, length);
16   g_free (contents);
17   TFE_TEXT_VIEW (tv)->file = g_file_dup (file);
18   return tv;
19 }
20 
21 GtkWidget *
22 tfe_text_view_new (void) {
23   return GTK_WIDGET (g_object_new (TFE_TYPE_TEXT_VIEW, NULL));
24 }

• 21-24: tfe_text_view_new function. Just returns the value from the function g_object_new but casts it to the pointer to GtkWidget. Initialization is done in tfe_text_view_init which is called in the process of g_object_new function.
• 1-19: tfe_text_view_new_with_file function.
• 3: g_return_val_if_fail is described in Glib API reference. It tests whether the argument file is a pointer to GFile. If it's true, then the program goes on to the next line. If it's false, then it returns NULL (the second argument) immediately. And at the same time it logs out the error message (usually the log is outputted to stderr or stdout). This function is used to check the programmer's error. If an error occurs, the solution is usually to change the (caller) program and fix the bug. You need to distinguish programmer's errors and runtime errors. You shouldn't use this function to find runtime errors.
• 10-11: If an error occurs when reading the file, then return NULL.
• 13: Calls the function tfe_text_view_new. The function creates TfeTextView instance and returns the pointer to the instance.
• 14: Gets the pointer to GtkTextBuffer corresponds to tv. The pointer is assigned to tb
• 15: Assigns the contents read from the file to GtkTextBuffer pointed by tb.
• 16: Frees the memories pointed by contents.
• 17: Duplicates file and sets tv->file to point it.
• 18: Returns tv, which is a pointer to the newly created TfeTextView instance..

Save and saveas functions

Save and saveas functions write the contents in GtkTextBuffer to a file.

void tfe_text_view_save (TfeTextView *tv)

The function save writes the contents in GtkTextBuffer to a file specified by tv->file. If tv->file is NULL, then it shows GtkFileChooserDialog and prompts the user to choose a file to save. Then it saves the contents to the file and sets tv->file to point the GFile of the file.

void tfe_text_view_saveas (TfeTextView *tv)

The function saveas uses GtkFileChooserDialog and prompts the user to select a existed file or specify a new file to save. Then, the function changes tv->file and save the contents to the specified file. If an error occurs, it is shown to the user through the message dialog. The error is managed only in the TfeTextView instance and no information is notified to the caller.

 1 static gboolean
 2 save_file (GFile *file, GtkTextBuffer *tb, GtkWindow *win) {
 3   GtkTextIter start_iter;
 4   GtkTextIter end_iter;
 5   gchar *contents;
 6   GtkWidget *message_dialog;
 7   GError *err = NULL;
 8 
 9   /* This function doesn't check G_IS_FILE (file). The caller should check it. */
10   gtk_text_buffer_get_bounds (tb, &start_iter, &end_iter);
11   contents = gtk_text_buffer_get_text (tb, &start_iter, &end_iter, FALSE);
12   if (g_file_replace_contents (file, contents, strlen (contents), NULL, TRUE, G_FILE_CREATE_NONE, NULL, NULL, &err)) {
13     gtk_text_buffer_set_modified (tb, FALSE);
14     return TRUE;
15   } else {
16     message_dialog = gtk_message_dialog_new (win, GTK_DIALOG_MODAL,
17                                              GTK_MESSAGE_ERROR, GTK_BUTTONS_CLOSE,
18                                             "%s.\n", err->message);
19     g_signal_connect (message_dialog, "response", G_CALLBACK (gtk_window_destroy), NULL);
20     gtk_widget_show (message_dialog);
21     g_error_free (err);
22     return FALSE;
23   }
24 }
25 
26 static void
27 saveas_dialog_response (GtkWidget *dialog, gint response, TfeTextView *tv) {
28   GtkTextBuffer *tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
29   GFile *file;
30   GtkWidget *win = gtk_widget_get_ancestor (GTK_WIDGET (tv), GTK_TYPE_WINDOW);
31 
32   if (response == GTK_RESPONSE_ACCEPT) {
33     file = gtk_file_chooser_get_file (GTK_FILE_CHOOSER (dialog));
34     if (! G_IS_FILE (file))
35       g_warning ("TfeTextView: gtk_file_chooser_get_file returns non GFile object.\n");
36     else if (save_file(file, tb, GTK_WINDOW (win))) {
37       if (G_IS_FILE (tv->file))
38         g_object_unref (tv->file);
39       tv->file = file;
40       g_signal_emit (tv, tfe_text_view_signals[CHANGE_FILE], 0);
41     }
42   }
43   gtk_window_destroy (GTK_WINDOW (dialog));
44 }
45 
46 void
47 tfe_text_view_save (TfeTextView *tv) {
48   g_return_if_fail (TFE_IS_TEXT_VIEW (tv));
49 
50   GtkTextBuffer *tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
51   GtkWidget *win = gtk_widget_get_ancestor (GTK_WIDGET (tv), GTK_TYPE_WINDOW);
52 
53   if (! gtk_text_buffer_get_modified (tb))
54     return; /* no need to save it */
55   else if (tv->file == NULL)
56     tfe_text_view_saveas (tv);
57   else if (! G_IS_FILE (tv->file))
58     g_error ("TfeTextView: The pointer in this object isn't NULL nor GFile object.\n");
59   else
60     save_file (tv->file, tb, GTK_WINDOW (win));
61 }
62 
63 void
64 tfe_text_view_saveas (TfeTextView *tv) {
65   g_return_if_fail (TFE_IS_TEXT_VIEW (tv));
66 
67   GtkWidget *dialog;
68   GtkWidget *win = gtk_widget_get_ancestor (GTK_WIDGET (tv), GTK_TYPE_WINDOW);
69 
70   dialog = gtk_file_chooser_dialog_new ("Save file", GTK_WINDOW (win), GTK_FILE_CHOOSER_ACTION_SAVE,
71                                       "Cancel", GTK_RESPONSE_CANCEL,
72                                       "Save", GTK_RESPONSE_ACCEPT,
73                                       NULL);
74   g_signal_connect (dialog, "response", G_CALLBACK (saveas_dialog_response), tv);
75   gtk_widget_show (dialog);
76 }

• 1-24: save_file function. This function is called from saveas_dialog_response and tfe_text_view_save. This function saves the contents of the buffer to the file given as an argument. If error happens, it displays an error message.
• 10-11: Gets the text contents from the buffer.
• 12-14: Saves the contents to the file. If it's been done without error, set the modified flag to be FALSE. This means that the buffer is not modified since it has been saved. And return TRUE to the caller.
• 15-22: If it's failed to save the contents, displays an error message. Creates a message dialog with the error message. Connects the "response" signal to gtk_window_destroy, so that the dialog disappears when a user clicked on the button. Shows the window, frees err and returns FLASE to the caller.
• 26-44: saveas_dialog_response function. This is a signal handler for a "response" signal on GtkFileChooserDialog created by tfe_text_view_saveas function. This handler analyzes the response and determines whether to save the contents.
• 32-44: If the response is GTK_RESPONSE_ACCEPT, the user has clicked on the Save button. So, it tries to save.
• 33-35: Gets the GFile file from GtkFileChooserDialog. If it doesn't point GFile, it outputs an error message to the log.
• 36-42: Otherwise, it calls save_file to save the contents to the file. tv->file is changed, but if the old GFile pointed by tv->file exists, it is freed in advance. Emits "change-file" signal.
• 46-61: Tfe_text_view_save function.
• 48: If tv is not a pointer to TfeTextView, then it logs an error message and immediately returns. This function is similar to g_return_val_if_fail function, but no value is returned because tfe_text_view_save doesn't return a value.
• 53-54: If the buffer hasn't modified, then it doesn't need to save it. So the function returns.
• 55-56: If tv->file is NULL, no file has given yet. It calls tfe_text_view_saveas which prompts a user to select a file or specify a new file to save.
• 57-58: If tv->file doesn't point GFile, somethig bad has happened. Logs an error message.
• 59-60: Calls save_file and saves the contents to the file. It is possible that save_filefails, but no notification will be given to the caller.
• 63-76: tfe_text_view_saveas function. It shows GtkFileChooserDialog and prompts the user to choose a file.
• 70-73: Creates GtkFileChooserDialog. The title is "Save file". Transient parent of the dialog is win, which is the top level window. The action is save mode. The buttons are Cancel and Save.
• 74: connects the "response" signal of the dialog and saveas_dialog_response handler.

When you use GtkFileChooserDialog, you need to divide the program into two parts. One is a function which creates GtkFileChooserDialog and the other is a signal handler. The function just creates and shows GtkFileChooserDialog. The rest is done by the handler. It gets Gfile from GtkFileChooserDialog and saves the buffer to the file by calling tfe_text_view_save.

Open function

Open function shows GtkFileChooserDialog to users and prompts them to choose a file. Then it reads the file and puts the text to GtkTextBuffer.

void tfe_text_view_open (TfeTextView *tv, GtkWindow *win);

The parameter win is the top level window. It will be a transient parent window of GtkFileChooserDialog when the dialog is created. This allows window managers to keep the dialog on top of the parent window, or center the dialog over the parent window. It is possible to give no parent window to the dialog. However, it is encouraged to give a parent window to dialog. This function might be called just after tv has been created. In that case, tv has not been incorporated into the widget hierarchy. Therefore it is impossible to get the top window from tv. That's why the function needs win parameter.

This function is usually called when the buffer of tv is empty. However, even if the buffer is not empty, tfe_text_view_open doesn't treat it as an error. If you want to revert the buffer, calling this function is appropriate. Otherwise probably bad things will happen.

 1 static void
 2 open_dialog_response(GtkWidget *dialog, gint response, TfeTextView *tv) {
 3   GtkTextBuffer *tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
 4   GFile *file;
 5   char *contents;
 6   gsize length;
 7   GtkWidget *message_dialog;
 8   GError *err = NULL;
 9 
10   if (response != GTK_RESPONSE_ACCEPT)
11     g_signal_emit (tv, tfe_text_view_signals[OPEN_RESPONSE], 0, TFE_OPEN_RESPONSE_CANCEL);
12   else if (! G_IS_FILE (file = gtk_file_chooser_get_file (GTK_FILE_CHOOSER (dialog)))) {
13     g_warning ("TfeTextView: gtk_file_chooser_get_file returns non GFile object.\n");
14     g_signal_emit (tv, tfe_text_view_signals[OPEN_RESPONSE], 0, TFE_OPEN_RESPONSE_ERROR);
15   } else if (! g_file_load_contents (file, NULL, &contents, &length, NULL, &err)) { /* read error */
16     if (G_IS_FILE (file))
17       g_object_unref (file);
18     message_dialog = gtk_message_dialog_new (GTK_WINDOW (dialog), GTK_DIALOG_MODAL,
19                                              GTK_MESSAGE_ERROR, GTK_BUTTONS_CLOSE,
20                                             "%s.\n", err->message);
21     g_signal_connect (message_dialog, "response", G_CALLBACK (gtk_window_destroy), NULL);
22     gtk_widget_show (message_dialog);
23     g_error_free (err);
24     g_signal_emit (tv, tfe_text_view_signals[OPEN_RESPONSE], 0, TFE_OPEN_RESPONSE_ERROR);
25   } else {
26     gtk_text_buffer_set_text (tb, contents, length);
27     g_free (contents);
28     if (G_IS_FILE (tv->file))
29       g_object_unref (tv->file);
30     tv->file = file;
31     gtk_text_buffer_set_modified (tb, FALSE);
32     g_signal_emit (tv, tfe_text_view_signals[OPEN_RESPONSE], 0, TFE_OPEN_RESPONSE_SUCCESS);
33     g_signal_emit (tv, tfe_text_view_signals[CHANGE_FILE], 0);
34   }
35   gtk_window_destroy (GTK_WINDOW (dialog));
36 }
37 
38 void
39 tfe_text_view_open (TfeTextView *tv, GtkWindow *win) {
40   g_return_if_fail (TFE_IS_TEXT_VIEW (tv));
41   g_return_if_fail (GTK_IS_WINDOW (win));
42 
43   GtkWidget *dialog;
44 
45   dialog = gtk_file_chooser_dialog_new ("Open file", win, GTK_FILE_CHOOSER_ACTION_OPEN,
46                                         "Cancel", GTK_RESPONSE_CANCEL,
47                                         "Open", GTK_RESPONSE_ACCEPT,
48                                         NULL);
49   g_signal_connect (dialog, "response", G_CALLBACK (open_dialog_response), tv);
50   gtk_widget_show (dialog);
51 }

• 38-51: tfe_text_view_open function.
• 45-48: Creates GtkFileChooserDialog. The title is "Open file". Transient parent window is the top level window of the application, which is given by the caller. The action is open mode. The buttons are Cancel and Open.
• 49: connects the "response" signal of the dialog and open_dialog_response signal handler.
• 50: Shows the dialog.
• 1-36: open_dialog_response signal handler.
• 10-11: If the response from GtkFileChooserDialog is not GTK_RESPONSE_ACCEPT, which means the user has clicked on the "Cancel" button or close button on the header bar, then it emits "open-response" signal with the parameter TFE_OPEN_RESPONSE_CANCEL.
• 12-14: Gets a pointer to Gfile by gtk_file_chooser_get_file. If it doesn't point GFile, maybe an error occurred. Then it emits "open-response" signal with the parameter TFE_OPEN_RESPONSE_ERROR.
• 15-24: If an error occurs at file reading, then it decreases the reference count of the Gfile, shows a message dialog to report the error to the user and emits "open-response" signal with the parameter TFE_OPEN_RESPONSE_ERROR.
• 25-33: If the file has successfully been read, then the text is inserted to GtkTextBuffer, frees the temporary buffer pointed by contents and sets tv->file to point the file (no duplication or unref is not necessary). Then, it emits "open-response" signal with the parameter TFE_OPEN_RESPONSE_SUCCESS and emits "change-file" signal.
• 35: closes GtkFileCooserDialog.

Now let's think about the whole process between the other object (caller) and TfeTextView. It is shown in the following diagram and you would think that it is really complicated. Because signal is the only way for GtkFileChooserDialog to communicate with others. In Gtk3, gtk_dialog_run function is available. It simplifies the process. However, in Gtk4, gtk_dialog_run is unavailable any more.

1. A caller gets a pointer tv to TfeTextView by calling tfe_text_view_new.
2. The caller connects the handler (left bottom in the diagram) and the signal "open-response".
3. It calls tfe_text_view_open to prompt the user to select a file from GtkFileChooserDialog.
4. The dialog emits a signal and it invokes the handler open_dialog_response.
5. The handler reads the file and inserts the text into GtkTextBuffer and emits a signal to inform the response status.
6. The handler outside TfeTextView receives the signal.

Get file function

gtk_text_view_get_file is a simple function shown as follows.

1 GFile *
2 tfe_text_view_get_file (TfeTextView *tv) {
3   g_return_val_if_fail (TFE_IS_TEXT_VIEW (tv), NULL);
4 
5   if (G_IS_FILE (tv->file))
6     return g_file_dup (tv->file);
7   else
8     return NULL;
9 }

The important thing is to duplicate tv->file. Otherwise, if the caller frees the GFile object, tv->file is no more guaranteed to point the GFile.

API document and source file of tfetextview.c

Refer API document of TfeTextView. It is under the directory src/tfetextview.

All the source files are listed in Section 15. You can find them under src/tfe5 and src/tfetextview directories.

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