Notifying The User With Toasts#

Toasts, or “in-app notifications”, are useful to communicate a change in state from within the application, or to gather feedback from the user.

In this lesson, you will learn how to add a toast overlay to the text viewer application, and how to display a toast when opening a file.

Add a toast overlay#

Toasts are displayed by an overlay, which must contain the rest of the application’s content area.

Update the UI definition file#

Find the UI definition file for TextViewerWindow
Find the definition for the GtkScrolledWindow that contains the main text area
Insert the AdwToastOverlay widget as the child of the TextViewerWindow and the parent of the GtkScrolledWindow, and use the toast_overlay id

<property name="content">
  <object class="AdwToastOverlay" id="toast_overlay">
    <property name="child">
      <object class="GtkScrolledWindow">
        <property name="hexpand">true</property>
        <property name="vexpand">true</property>
        <property name="margin-top">6</property>
        <property name="margin-bottom">6</property>
        <property name="margin-start">6</property>
        <property name="margin-end">6</property>
        <property name="child">
          <object class="GtkTextView" id="main_text_view">
            <property name="monospace">true</property>
          </object>
        </property>
      </object>
    </property>
  </object>
</property>

Bind the overlay in the source#

You now must add a new member to the TextViewerWindow instance structure for the toast_overlay widget:

struct _TextViewerWindow
{
  AdwApplicationWindow  parent_instance;

  /* Template widgets */
  AdwHeaderBar *header_bar;
  GtkTextView *main_text_view;
  GtkButton *open_button;
  GtkLabel *cursor_pos;
  AdwToastOverlay *toast_overlay;
};

Bind the newly added toast_overlay widget to the template in the class initialization function text_viewer_window_class_init of the TextViewerWindow type:

static void
text_viewer_window_class_init (TextViewerWindowClass *klass)
{
  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);

  gtk_widget_class_set_template_from_resource (widget_class, "/com/example/TextViewer/text_viewer-window.ui");
  gtk_widget_class_bind_template_child (widget_class, TextViewerWindow, header_bar);
  gtk_widget_class_bind_template_child (widget_class, TextViewerWindow, main_text_view);
  gtk_widget_class_bind_template_child (widget_class, TextViewerWindow, open_button);
  gtk_widget_class_bind_template_child (widget_class, TextViewerWindow, cursor_pos);
  gtk_widget_class_bind_template_child (widget_class, TextViewerWindow, toast_overlay);
}

Add the toast_overlay widget to the TextViewerWindow class

@Gtk.Template(resource_path='/com/example/TextViewer/window.ui')
class TextViewerWindow(Adw.ApplicationWindow):
    __gtype_name__ = 'TextViewerWindow'

    main_text_view = Gtk.Template.Child()
    open_button = Gtk.Template.Child()
    cursor_pos = Gtk.Template.Child()
    toast_overlay = Gtk.Template.Child()

Add the toast_overlay widget to the TextViewer.Window class

[GtkTemplate (ui = "/org/example/app/window.ui")]
public class TextViewer.Window : Adw.ApplicationWindow {
    [GtkChild]
    private unowned Gtk.TextView main_text_view;

    [GtkChild]
    private unowned Gtk.Button open_button;

    [GtkChild]
    private unowned Gtk.Label cursor_pos;

    [GtkChild]
    private unowned Adw.ToastOverlay toast_overlay;

    // ...
}

Show toasts#

Toasts are especially useful for notifying the user that an asynchronous operation has terminated. Opening a file and saving it are two typical use cases for a notification.

Notify after opening a file#

Find the open_file_complete function for TextViewerWindow
Find the error handling blocks and replace them with a toast
Add a toast at the end of the function

static void
open_file_complete (GObject          *source_object,
                    GAsyncResult     *result,
                    TextViewerWindow *self)
{
  GFile *file = G_FILE (source_object);

  g_autofree char *contents = NULL;
  gsize length = 0;

  g_autoptr (GError) error = NULL;

  // Complete the asynchronous operation; this function will either
  // give you the contents of the file as a byte array, or will
  // set the error argument
  g_file_load_contents_finish (file,
                               result,
                               &contents,
                               &length,
                               NULL,
                               &error);

  // Query the display name for the file
  g_autofree char *display_name = NULL;
  g_autoptr (GFileInfo) info =
  g_file_query_info (file,
                     "standard::display-name",
                     G_FILE_QUERY_INFO_NONE,
                     NULL,
                     NULL);
  if (info != NULL)
    {
      display_name =
        g_strdup (g_file_info_get_attribute_string (info, "standard::display-name"));
    }
  else
    {
      display_name = g_file_get_basename (file);
    }

  // In case of error, show a toast
  if (error != NULL)
    {
      g_autofree char *msg =
        g_strdup_printf ("Unable to open “%s”", display_name);

      adw_toast_overlay_add_toast (self->toast_overlay, adw_toast_new (msg));
      return;
    }

  // Ensure that the file is encoded with UTF-8
  if (!g_utf8_validate (contents, length, NULL))
    {
      g_autofree char *msg =
        g_strdup_printf ("Invalid text encoding for “%s”", display_name);

      adw_toast_overlay_add_toast (self->toast_overlay, adw_toast_new (msg));
      return;
    }

  // Retrieve the GtkTextBuffer instance that stores the
  // text displayed by the GtkTextView widget
  GtkTextBuffer *buffer = gtk_text_view_get_buffer (self->main_text_view);

  // Set the text using the contents of the file
  gtk_text_buffer_set_text (buffer, contents, length);

  // Reposition the cursor so it's at the start of the text
  GtkTextIter start;
  gtk_text_buffer_get_start_iter (buffer, &start);
  gtk_text_buffer_place_cursor (buffer, &start);

  // Set the title using the display name
  gtk_window_set_title (GTK_WINDOW (self), display_name);

  // Show a toast for the successful loading
  g_autofree char *msg =
    g_strdup_printf ("Opened “%s”", display_name);

  adw_toast_overlay_add_toast (self->toast_overlay, adw_toast_new (msg));
}

def open_file_complete(self, file, result):
    info = file.query_info("standard::display-name", Gio.FileQueryInfoFlags.NONE)
    if info:
        display_name = info.get_attribute_string("standard::display-name")
    else:
        display_name = file.get_basename()

    contents = file.load_contents_finish(result)

    if not contents[0]:
        self.toast_overlay.add_toast(Adw.Toast(title=f"Unable to open “{display_name}”"))
        return

    try:
        text = contents[1].decode('utf-8')
    except UnicodeError as err:
        self.toast_overlay.add_toast(Adw.Toast(title=f"Invalid text encoding for “{display_name}”")
        return

    buffer = self.main_text_view.get_buffer()
    buffer.set_text(text)
    start = buffer.get_start_iter()
    buffer.place_cursor(start)

    self.set_title(display_name)
    self.toast_overlay.add_toast(Adw.Toast(title=f"Opened “{display_name}”"))

private void open_file (File file) {
    file.load_contents_async.begin (null, (object, result) => {
        string display_name;
        // Query the display name for the file
        try {
            FileInfo? info = file.query_info ("standard::displayname", FileQueryInfoFlags.NONE);
            display_name = info.get_attribute_string ("standard::displayname");
        } catch (Error e) {
            display_name = file.get_basename ();
        }

        uint8[] contents;
        try {
            // Complete the asynchronous operation; this function will either
            // give you the contents of the file as a byte array, or will
            // raise an exception
            file.load_contents_async.end (result, out contents, null);
        } catch (Error e) {
            // In case of an error, show a toast
            this.toast_overlay.add_toast (new Adw.Toast (@"Unable to open “$display_name“"));
        }

        // Ensure that the file is encoded with UTF-8
        if (!((string) contents).validate ())
            this.toast_overlay.add_toast (new Adw.Toast (@"Invalid text encoding for “$display_name“"));

        // Retrieve the GtkTextBuffer instance that stores the
        // text displayed by the GtkTextView widget
        Gtk.TextBuffer buffer = this.main_text_view.buffer;

        // Set the text using the contents of the file
        buffer.text = (string) contents;

        // Reposition the cursor so it's at the start of the text
        Gtk.TextIter start;
        buffer.get_start_iter (out start);
        buffer.place_cursor (start);

        // Set the title using the display name
        this.title = display_name;

        // Show a toast for the successful loading
        this.toast_overlay.add_toast (new Adw.Toast (@"Opened “$display_name“"));
    });
}

Notify after saving to a file#

In the save_file_complete function you can use a toast to notify the user that the operation succeeded or failed

static void
save_file_complete (GObject          *source_object,
                    GAsyncResult     *result,
                    TextViewerWindow *self)
{
  GFile *file = G_FILE (source_object);

  g_autoptr (GError) error =  NULL;
  g_file_replace_contents_finish (file, result, NULL, &error);

  // Query the display name for the file
  g_autofree char *display_name = NULL;
  g_autoptr (GFileInfo) info =
  g_file_query_info (file,
                     "standard::display-name",
                     G_FILE_QUERY_INFO_NONE,
                     NULL,
                     NULL);
  if (info != NULL)
    {
      display_name =
        g_strdup (g_file_info_get_attribute_string (info, "standard::display-name"));
    }
  else
    {
      display_name = g_file_get_basename (file);
    }

  g_autofree char *msg = NULL;
  if (error != NULL)
    msg = g_strdup_printf ("Unable to save as “%s”", display_name);
  else
    msg = g_strdup_printf ("Saved as “%s”", display_name);

  adw_toast_overlay_add_toast (self->toast_overlay, adw_toast_new (msg));
}

def save_file_complete(self, file, result):
    res = file.replace_contents_finish(result)
    # Query the display name for the file
    info = file.query_info("standard::display-name",
                           Gio.FileQueryInfoFlags.NONE)
    if info:
        display_name = info.get_attribute_string("standard::display-name")
    else:
        display_name = file.get_basename()
    if not res:
        msg = f"Unable to save as “{display_name}”")
    else:
        msg = f"Saved as “{display_name}”"
    self.toast_overlay.add_toast(Adw.Toast(title=msg))

private void save_file (File file) {
    Gtk.TextBuffer buffer = this.main_text_view.buffer;

    // Retrieve the iterator at the start of the buffer
    Gtk.TextIter start;
    buffer.get_start_iter (start);

    // Retrieve the iterator at the end of the buffer
    Gtk.TextIter end;
    buffer.get_end_iter (end);

    // Retrieve all the visible text between the two bounds
    string? text = buffer.get_text (start, end, false);

    if (text == null || text.length == 0)
        return;

    var bytes = new Bytes.take (text);

    file.replace_contents_bytes_async.begin (bytes, null, false, FileCreateFlags.NONE, (object, result) => {
        string display_name;
        // Query the display name for the file
        try {
            FileInfo info = file.query_info ("standard::display-name",
                                             FileQueryInfoFlags.NONE);
            display_name = info.get_attribute_string ("standard::display-name");
        } catch (Error e) {
            display_name = file.get_basename ();
        }

        string message;

        try {
            file.replace_contents_async.end (result, null);
            message = @"Unable to save as “$display_name“";
        } catch (Error e) {
            message = @"Saved as “$display_name“";
        }

        this.toast_overlay.add_toast (new Adw.Toast (message));
    });
}

In this lesson you learned how to notify the user of a long running operation that either succeeded or failed using toasts.