I am looking into GUI development with Racket. I would like to create a tab-panel%, with multiple tabs. The documentation says, that a switch of tab does only call a procedure and does not make a content change happen automatically. I think this is quite clever behavior, but I have a problem implementing an initially empty tab-panel, which only gets content (children) when I select one of the tabs.
This is the code I already have:
#lang racket/gui
(require racket/gui/base)
(define nil '())
(define application-frame
(new frame%
[label "Example"]
[width 400]
[height 300]))
(define menu-bar
(new menu-bar%
[parent application-frame]))
(define file-menu
(new menu%
[label "&File"]
[parent menu-bar]))
(new menu%
[label "&Edit"]
[parent menu-bar])
(new menu%
[label "&Help"]
[parent menu-bar])
(new menu-item%
[label "E&xit"]
[parent file-menu]
[callback
(λ (m event)
(exit nil))])
(define tab-panel
(new tab-panel%
[parent application-frame]
[choices '("&Lookup" "&Training")]
[callback
(λ (tp event)
(case (send tp get-item-label (send tp get-selection))
[("&Lookup")
(send tp change-children
(λ (children)
(list lookup-panel)))]
[("&Training")
(send tp change-children
(λ (children)
(list training-panel)))]))]))
(define get-lookup-panel
(lambda (children)
(let
[(lookup-panel (new panel% [parent tab-panel]))]
[(new message%
[parent lookup-panel]
[label "The content of the lookup panel for the lookup tab."])
lookup-panel])))
(define lookup-panel (new panel% [parent tab-panel]))
(define lookup-panel-content
(new message%
[parent lookup-panel]
[label "The content of the lookup panel for the lookup tab."]))
(define training-panel (new panel% [parent tab-panel]))
(define training-panel-content
(new message%
[parent training-panel]
[label "The content of the training panel for the training tab."]))
(define status-message
(new message%
[parent application-frame]
[label "No events so far..."]
[auto-resize #t]))
(send application-frame show #t)
The problem here is, that initially both children of the tab-panel are visible, although (naturally) only one tab is selected. When I change tab, the behavior is corrected by the lambdas inside the case form.
However, I cannot simply give those panels, which I set as children no parent, because racket will tell me, that I need to specify the required initial argument parent. This means they will be initially added to the tab-panel. Is it necessary to create the panels and then again remove them from the tab-panel? That would seem a bit dirty. I think there is probably a better way.
I already tried to dynamically create the panel, as can be seen in the get-lookup-panel procedure, but I couldn't get that to work in the case form.
What is the correct way to implement it?
edit1
I found a way to define a procedure, which can be used in the way I want to use it:
(define (get-lookup-panel4 children)
(define lookup-panel (new panel% [parent tab-panel]))
(define lookup-panel-message (new message% [parent lookup-panel] [label "LOOKUP"]))
(list lookup-panel))
Which can be used as follows:
(define tab-panel
(new tab-panel%
[parent application-frame]
[choices '("&Lookup" "&Training")]
[callback
(λ (tp event)
(case (send tp get-item-label (send tp get-selection))
[("&Lookup")
(send tp change-children get-lookup-panel4)]
[("&Training")
(send tp change-children
(λ (children)
(list training-panel)))]))]))
But I don't understand what the difference between this procedure and the other one with the let expression is and another problem with this approach is, that I cannot afterwards modify the created panel or message, because their scope is the procedure.
