How to write plugins for gedit

This is a comprehensive guide on writing plugins for gedit in Python3.

Requirements

Structure

  • name.plugin It tells gedit where the plugin is found. It contains author’s details. This file is in .desktop format.

  • name.py or name/__init.py__ This file contains the actual code. It can also be a python package.

Both files are placed in either /usr/lib/gedit/plugins/ (system-wide) or ~/.local/share/gedit/plugins/ (single-user).

gedit plugin interfaces

This section will try to explain how gedit plugins work.

A Python plugin will be able to have one or more extensions. Each extension is derived from GObject.Object and must implement one of the interfaces that gedit provides for the extension points. These define the entry points in your code.

All extension points will have the defined gedit object as a property.

Example: Extension point from gedit.AppActivatable will have app property and hence would be able to use Gedit.App API.

Refer to the following list to know which interface should be used and when:

  • Gedit.AppActivatable : App

    Provides do_activate, do_deactivate.
    gedit usually only runs one instance, even if you launch it several times hence, you can get application menu extension, or can initialize singleton objects using this interface.

  • Gedit.WindowActivatable : Window

    Provides do_activate, do_deactivate, do_update_state.
    Should be used when you want to change/delete/create tabs, to access bottom bar, etc.

  • Gedit.ViewActivatable : View

    Provides do_activate, do_deactivate, do_update_state.
    When operations on all views are required. Like removing trailing whitespaces on document save.

do_activate is called in the extension point when gedit object of its defined type is created.

do_deactivate is called in the extension point when gedit object of its defined type is destroyed.

do_update_state is called in the extension point when gedit object of its defined type needs a UI update.

Example: Gedit.WindowActivatable.do_activate is called when a window object is created.

When a plugin is activated, all “activate” methods from the extension points will be called, and when the plugin is deactivated the “deactivate” methods from all extension points will be called.

Example Plugin

Let us create an example plugin which instantly clears the document.

  • Plugin File

    [Plugin]
    Loader=python3
    Module=example
    IAge=3
    Name=Example
    Icon=example
    Description=An example plugin which clears the document.
    Authors= theawless <theawless@gmail.com>
    Copyright=Copyright © 2016 Abhinav Singh <theawless@gmail.com>
    Website=https://github.com/theawless/Clear-Doc
    

    Most of the fields are pretty obvious in the .plugin file. Here are some tips

    • IAge is always 3.
    • Module does not have .py extension. And you can also specify a package here.
    • Icon

      You should install your icon in $prefix/share/icons/hicolor/scalable/apps and then update the icon cache using command gtk-update-icon-cache-3.0.
      Read more about icon specification here.

  • Imports

    PeasGtk for implementing settings – more on this later
    Gio for menu
    Gtk is the gnome’s UI library
    Gedit for gedit’s API functions
    GObject : Fundamental object. Many gnome libraries like Gtk, Pango inherit from it

    from gi.repository import GObject, Gtk, Gedit, PeasGtk, Gio
    
  • Activatable

    Let’s define a basic Activatable.

    class ExampleAppActivatable(GObject.Object, Gedit.AppActivatable):
      app = GObject.property(type=Gedit.App)
      __gtype_name__ = "ExampleAppActivatable"
    
      def __init__(self):
          GObject.Object.__init__(self)
    
      def do_activate(self):
          pass
    
      def do_deactivate(self):
          pass
    
  • Menu

    Gedit.AppActivatable: We need to create an AppActivatable class first. We insert the menu to the main menu and set accelerators(keyboard shortcuts). Real action is defined later. Menu creation should be done in do_activate and deletion should be done in do_deactivate. You should read about Gio.Menu.

      #call me in do_activate
      def _build_menu(self):
          # Get the extension from tools menu        
          self.menu_ext = self.extend_menu("tools-section")
          # This is the submenu which is added to a menu item and then inserted in tools menu.        
          menu = Gio.Menu()
          sub_menu_item = Gio.MenuItem.new("Clear Document", 'win.clear_document')
          menu.append_item(sub_menu_item)
          self.menu_item = Gio.MenuItem.new_submenu("Example", menu)
          self.menu_ext.append_menu_item(self.menu_item)
          # Setting accelerators, now our action is called when Ctrl+Alt+1 is pressed.
          self.app.set_accels_for_action("win.clear_document", ("<Primary><Alt>1", None))
    
      #call me in do_deactivate
      def _remove_menu(self):
          # removing accelerator and destroying menu items
          self.app.set_accels_for_action("win.dictonator_start", ())
          self.menu_ext = None
          self.menu_item = None
    

    Gedit.WindowActivatable: We need to create a WindowActivatable class too. Here we connect to the menu and define the action of clearing the document. We will connect the action to a callback function. That’s how signals (similar to events) are used in Gtk. As soon as activate is fired, action_cb is called. It’s now clear why we used WindowActivatable. It has the power to give us the active document so that we can clear it.

      #call me in do_activate
      def _connect_menu(self):
          action = Gio.SimpleAction(name='clear_document')
          action.connect('activate', self.action_cb)
          self.window.add_action(action)
    
      def action_cb(self, action, data):
          # On action clear the document.
          doc = self.window.get_active_document()
          doc.set_text("")
    
      # this is called every time the gui is updated
      def do_update_state(self):
          # if there is no document in sight, we disable the action, so we don't get NoneException
          if self.window.get_active_view() is not None:
              self.window.lookup_action('clear_document').set_enabled(true)
    

    However weird it may seem; here, gui for menu is created in Gedit.AppActivatable while action is defined in Gedit.WindowActivatable. Gtk supports app-menu(which is available for all windows) and window-menu(which is defined for each window). Now because gedit is a single window application, but it creates the menu in appmenu, we have to first create AppActivatable. It may be a little hard to understand for those new to Gtk.

  • Bottom Panel/Side Panel

    The bottom panel is a Gtk.Stack. You will need to learn to read the C documentation for Gnome Libraries, because Python Documentation is out-dated and incomplete. Addition of bottom panel should also be done in do_activate.

      #call me in do_activate
      def _insert_bottom_panel(self):
          # Add elements to panel.
          self.bottom_bar.add(Gtk.Label("Hello There!"))
          # Get bottom bar (A Gtk.Stack) and add our bar.        
          panel = self.window.get_bottom_panel()
          panel.add_titled(self.bottom_bar, 'example', "Example")
          # Make sure everything shows up.
          panel.show()
          self.bottom_bar.show_all()
          panel.set_visible_child(self.bottom_bar)
    
      #call me in do_deactivate
      def _remove_bottom_panel(self):
          panel = self.window.get_bottom_panel()
          panel.remove(self.bottom_bar)
    
  • Configuration Dialog

    Let’s implement the configurable dialog, it can be used to change plugin settings. First we need to inherit from PeasGtk.Configurable

    class ExampleWindowActivatable(GObject.Object, Gedit.WindowActivatable, PeasGtk.Configurable):
      window = GObject.property(type=Gedit.Window)
      __gtype_name__ = "ExampleWindowActivatable"
    
      def __init__(self):
          GObject.Object.__init__(self)
    
      def do_create_configure_widget(self):
          # Just return your box, PeasGtk will automatically pack it into a box and show it.
          box=Gtk.Box()
          box.add(Gtk.Label("Settings Here!"))
          return box
    

Source Code

Get the full source code of the Example Plugin.
You can also visit Dict’O’nator, a dictation plugin I wrote for gedit.

Reference Pages

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