Smalltalk and Object Orientation: an Introduction - Free

27.3 VisualWorks window painting tools
Figure 27.1: The user interface builder and resource Launcher buttons
The VisualWorks user interface builder is initiated using the canvas tool button on the VisualLauncher.
This button has a picture of an easel with an artist’s canvas on it (see Figure 27.1). The user interface
builder is comprised of three tools. These tools are the palette, which contains the elements to be placed
on a window, the canvas, which is the drawing area for the window and the canvas tool, which allows
the user to issue specific commands such as the installation of a window.
The user interface builder in VisualWorks allows the user to create the window of an application
from a wide range of visual components. These visual components are available from the Palette and
include components such as buttons, text, sliders, tables and static visuals like rectangles and lines.
Using these components the user can build up a window much in the same way as a diagram might be
drawn in an object based drawing tool.
The user interface builder also provides a set of layout options in the canvas tool for relative and
absolute positioning and sizing, alignment and grouping of objects. Again this is done in a similar
manner to that of an object based drawing tool.
Figure 27.2 illustrates the window painting facilities being used to draw a modified VisualLauncher.
On the left of the diagram is the Palette on which iconic versions of graphic objects are made available
to the user. On the right of the Palette is the canvas on which the l ayout of the window is drawn.
Additional tools are available which allow the user to specify the properties associated with the graphic
objects, for example, it is possible to specify what action should be performed when a button is pressed
etc. The Canvas Control is displayed above the canvas window. This window allows the properties of
the canvas to be specified.
Figure 27.2: Creating a new Launcher using the window painting facilities
It is also possible for the user to generate an actual working version of the window which has just
been painted. This can be done by first installing the window. This actually generates a class definition
for the window. However, this is o nly the first step towards generating a functioning window. It is then
necessary to create the appropriate methods for displaying and updating values displayed in the window
and to produce stub methods for any actions which should be associated with the gr aphic objects in the
window. Such information can be entered by the user via the definer option in the canvas tool. This
generates accessor methods for the variables referred to or stub methods for the actions entered earlier
by the user. These stub method s must then be “filed out” with Smalltalk code using the standard set of
browsers.
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