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Aggregating Widgets in a Single Widget

Problem

You would like to deal with many widgets as though they were a single widget.

Solution

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

Addenda

this can be done as a macro;

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

-- StephenDeGabrielle - 17 Jul 2008

Discussion

GUI programming is non-standard. A PLT Solution has been given.

When designing a GUI, it is common to design widget groups that are reused. This is done by creating a subclass of the panel type and defining the widgets in that class.

The above sample displays a push button with the label "Push Me" above a Text Box with the label "Enter Text".

The first thing to do is start scheme with the graphics toolkit enabled:

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

(this is equivalent to importing the required libraries)

Then, we would like to define a new widget class and bind it to a name. It is customary to name classes with a % suffix. This will be a subclass of the vertical-panel% widget which will provide layout geometry for child widgets.

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

Since panel widgets cannot be top level windows (frames in the MrEd and wxWidget nomenclature), we must give this widget a parent that must be set on instantiation. This is done with the init-field expression:

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

If we wanted, we could set it to an initial value much the same way we set initial values in a let expression.

Next instantiate the vertical-panel[Initialize the superclass]. As we mentioned before, panels cannot be top level windows, so they must have parents. That means we need to pass the parent parameter to the super-instantiate expression:

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

Don't worry that the parent expression has the same name as the parameter. The values are resolved by position in the expression as well as name, so Scheme won't be confused.

The next step is to instantiate the component widgets. This is quite straight forward:

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

The keyword ''this'' allows us to place the component widgets (button and text-field) within the vertical-panel.

Constructing and showing the window are straight forward: 500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)


Comments about this recipe

Refactored to include changes suggested by comments and updated for PLT-Scheme 4+. (please see the history)

Thanks to DanielSilva and EwanHiggs

-- StephenDeGabrielle - 16 Jul 2008

Here is another example - but but the widget is created from drawing toolkit elements, rather than existing widgets.

500 Can't connect to 127.0.0.1:8778 (connect: Connection refused)

-- StephenDeGabrielle - 21 Sep 2007

Contributors

-- EwanHiggs - 01 Sep 2004

CookbookForm
TopicType: Recipe
ParentTopic: GUIRecipes
TopicOrder: 030

 
 
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