Chapter 22. Plugs and Sockets

# Chapter 22. Plugs and Sockets

## Overview

From time to time, it may be useful to be able to embed a widget from another application within your application. gtkmm allows you to do this with the `Gtk::Socket` and `Gtk::Plug` classes. It is not anticipated that very many applications will need this functionality, but in the rare case that you need to display a widget that is running in a completely different process, these classes can be very helpful.

The communication between a `Socket` and a `Plug` follows the XEmbed protocol. This protocol has also been implemented in other toolkits (e.g. Qt), which allows the same level of integration when embedding a Qt widget in GTK+ or vice versa.

The way that `Sockets` and `Plugs` work together is through their window ids. Both a `Socket` and a `Plug` have IDs that can be retrieved with their `get_id()` member functions. The use of these IDs will be explained below in the section called “Connecting Plugs and Sockets”.

### Sockets

A `Socket` is a special kind of container widget that provides the ability to embed widgets from one process into another process in a way that is transparent to the user.

### Plugs

A `Plug` is a special kind of Window that can be plugged into a `Socket`. Besides the normal properties and methods of `Gtk::Window`, a `Plug` provides a constructor that takes the ID of a `Socket`, which will automatically embed the `Plug` into the `Socket` that matches that ID.

Since a `Plug` is just a special type of `Gtk::Window` class, you can add containers or widgets to it like you would to any other window.

### Connecting Plugs and Sockets

After a `Socket` or `Plug` object is realized, you can obtain its ID with its `get_id()` function. This ID can then be shared with other processes so that other processes know how to connect to each other.

There are two basic strategies that can be used:

- Create a `Socket` object in one process and pass the ID of that `Socket` to another process so that it can create a `Plug` object by specifying the given `Socket` ID in its constructor. There is no way to assign a `Plug` to a particular `Socket` after creation, so you must pass the `Socket` ID to the `Plug`'s constructor.

- Create a `Plug` independantly from any particular `Socket` and pass the ID of the `Plug` to other processes that need to use it. The ID of the `Plug` can be associated with a particular `Socket` object using the `Socket::add_id()` function. This is the approach used in the example below.

RecentChooser |  | Plugs and Sockets Example