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Creating a window containing text

Problem

You want to create a GUI window containing some text.

Solution

PltScheme provides a cross-platform GUI toolkit called MrEd. MrEd builds upon the PltScheme's default object system, contained in the class.ss library in MzLib?.

Code to create a window and display the text "Hello World!" is:

(require (lib "mred.ss" "mred")
         (lib "class.ss" "mzlib"))

(define the-frame
  (new frame%
       (label "Hello!")
       (width 400)
       (height 400)))

(define the-pane
  (new pane%
       (parent the-frame)))

(define the-message
  (new message%
       (label "Hello World!")
       (parent the-pane)))

(send the-frame show #t)

Discussion

Like most GUI systems, MrEd consists of a hierarchy of graphical containers and containees.

A frame is a top-level container (meaning it has no parent container) that corresponds to a window. The code to create a frame with the given label (titlebar), height, and width is:

(define the-frame
  (new frame%
       (label "Hello!")
       (width 400)
       (height 400)))

A pane is another container that exists only to manage the layout of its children objects. In this example we don't need a pane, as with only one child, the message, there is no layout to manage. More complex examples will need to use panes. The code is create a pane is given below. Note that the parent is set to the frame.

(define the-pane
  (new pane%
       (parent the-frame)))

The message is an containee object that displays a text string. The code to create it is given below. Note how the parent is set to the pane. We could change the pane to the frame and this example would still work.

(define the-message
  (new message%
       (label "Hello World!")
       (parent the-pane)))

To actually get a frame drawn on the screen it is necessary to tell the frame to draw itself. This is done by sending the frame a draw message:

(send the-frame show #t)

Comments about this recipe

Contributors

-- NoelWelsh - 10 May 2005