code: def save_figure(self, *args):
      dialog = Gtk.FileChooserNative(
          title="Save the figure",
          transient_for=self.canvas.get_root(),
          action=Gtk.FileChooserAction.SAVE,
          modal=True,
      )
      self._save_dialog = dialog  # Must keep a reference.
  
      ff = Gtk.FileFilter()
      ff.set_name("All files")
      ff.add_pattern("*")
      dialog.add_filter(ff)
      dialog.set_filter(ff)
  
      formats = []
      default_format = None
      for i, (name, fmts) in enumerate(
          self.canvas.get_supported_filetypes_grouped().items()
      ):
          ff = Gtk.FileFilter()
          ff.set_name(name)
          for fmt in fmts:
              ff.add_pattern(f"*.{fmt}")
          dialog.add_filter(ff)
          formats.append(name)
          if self.canvas.get_default_filetype() in fmts:
              default_format = i
      # Setting the choice doesn't always work, so make sure the default
      # format is first.
      formats = [
          formats[default_format],
          *formats[:default_format],
          *formats[default_format + 1 :],
      ]
      dialog.add_choice("format", "File format", formats, formats)
      dialog.set_choice("format", formats[default_format])
  
      dialog.set_current_folder(
          Gio.File.new_for_path(
              os.path.expanduser(mpl.rcParams["savefig.directory"])
          )
      )
      dialog.set_current_name(self.canvas.get_default_filename())
  
      @functools.partial(dialog.connect, "response")
      def on_response(dialog, response):
          file = dialog.get_file()
          fmt = dialog.get_choice("format")
          fmt = self.canvas.get_supported_filetypes_grouped()[fmt][0]
          dialog.destroy()
          self._save_dialog = None
          if response != Gtk.ResponseType.ACCEPT:
              return
          # Save dir for next time, unless empty str (which means use cwd).
          if mpl.rcParams["savefig.directory"]:
              parent = file.get_parent()
              mpl.rcParams["savefig.directory"] = parent.get_path()
          try:
              self.canvas.figure.savefig(file.get_path(), format=fmt)
          except Exception as e:
              msg = Gtk.MessageDialog(
                  transient_for=self.canvas.get_root(),
                  message_type=Gtk.MessageType.ERROR,
                  buttons=Gtk.ButtonsType.OK,
                  modal=True,
                  text=str(e),
              )
              msg.show()
  
      dialog.show()
  
imports: import functools
  import io
  import os
  import matplotlib
  from matplotlib import _api, backend_tools, cbook
  from matplotlib.backend_bases import ToolContainerBase, KeyEvent, LocationEvent, MouseEvent, ResizeEvent, CloseEvent
  from gi.repository import Gio, GLib, Gtk, Gdk, GdkPixbuf
  from .None import _backend_gtk
  from ._backend_gtk import _BackendGTK, _FigureCanvasGTK, _FigureManagerGTK, _NavigationToolbar2GTK, TimerGTK
label_desc: Use image node_id 2 for calling the NavigationToolbar2GTK4 obj's underlying member method code with example usage: obj.save_figure() without return types