Ruby/Tk Tutorial


Ruby/Tk provides Ruby with a graphical user interface (GUI). The Tk extension works on Windows, Mac OS X and Unix systems.

Previous versions of the Ruby One-Click Installer contained an (old) version of Tcl/Tk. Now this Ruby installer only contains the Ruby bindings to whatever version of Tcl/Tk you wish to install. It's recommended to use ActiveTcl. Download the file ActiveTcl8. and install it. Reboot your PC.

Tk works along a composition model - that is, you start by creating a container (such as a TkFrame or TkRoot) and then create widgets (GUI components) that populate it, such as buttons or labels. When you are ready to start the GUI, you invoke Tk.mainloop. The Tk engine then takes control of the program, displaying widgets and calling your code in response to GUI events.

Simple Tk applications

Let's understand the following program p074hellotk.rb

The Tk documentation shows the class hierarchy. Briefly, the hierarchy is as follows:


There are many modules like:
Tk, Tk::Wm and many others.

TkKernel is the superclass of TkObject. The subclass redefines the class method new to take a block.
TkObject is the superclass of all widgets and has an included Tk module.
TkRoot class represents the root widget. The root widget is at the top of the Ruby/Tk widget hierarchy and has the included module Tk::Wm for communicating with a window manager. The methods introduced here are normally used as instance methods of TkRoot.

In the program, after loading the tk extension module, we create a root-level frame using With Tk you create widgets and then bind code blocks to them. When something happens (like the user clicking a widget), Tk runs the appropriate code block. In our program, we use the title and minsize instance methods (of module Tk::Wm) in the code block to We are now ready with our GUI and we invoke Tk.mainloop

Let us now add some widgets to the above program, namely a TkLabel. The modified program is p075hellotk1.rb

Here, we make a TkLabel widget (representing a label) as a child of the root frame, setting several options for the label. Finally, we pack the root frame and enter the main GUI event loop.

We also need to be able to get information back from our widgets while our program is running by setting up callbacks (routines invoked when certain events happen) and sharing data. The next example, p076hellotk2.rb does that.

Callbacks are very easy to setup. The command option takes a Proc object, which will be called when the callback fires. This means that the code block passed into the command method is run when the user clicks the button, allowing you to programmatically execute the same functionality that would be invoked on an actual button press. Note that the Kernel#exit method terminates your program here.

We shall now build a rudimentary GUI interface to our SOAP server hosted at The program is the p077soapguiclient.rb

Logger class

In the above program, we reconfigure a widget while it's running. Every widget supports the configure method, which takes a code block in the same manner as new. We have also modified the earlier p072soapserver.rb program, as below. We have included the Logger class.

The Logger class helps write log messages to a file or stream. It supports time- or size-based rolling of log files. Messages can be assigned severities, and only those messages at or above the logger's current reporting level will be logged. Here, we log to a file called soapserver.log, which is rotated when it gets about 10K bytes and keeps up to five old files.