[racket] how to tell, or trigger, on when an object is ready in tool on on startup

Hi,

I'm working on the tools facilities to build extensions for DrRacket,
and I'm having some trouble;

I think I'm getting the ''send: target is not an object: #<undefined>
for method: is-shown?
'' error on startup because the frame, tabs or text% is not yet
finished starting up.

I'd appreciate any help on how to run my method when DrRacket is ready?

Cheers,

Stephen


-- 
send: target is not an object: #<undefined> for method: is-shown?

 === context ===
/Applications/Racket
v5.0/collects/racket/private/class-internal.rkt:4543:0: obj-error
/Applications/Racket
v5.0/collects/racket/private/class-internal.rkt:3786:0:
find-method/who
/Applications/Racket
v5.0/collects/gui-debugger/debug-tool.rkt:1404:10:
check-current-language-for-debugger method in
...ugger/debug-tool.rkt:1048:8
/Applications/Racket
v5.0/collects/gui-debugger/debug-tool.rkt:1393:10: on-tab-change
method in ...ugger/debug-tool.rkt:1048:8
/Applications/Racket v5.0/collects/drracket/syncheck.rkt:1027:8:
on-tab-change method in ...rracket/syncheck.rkt:1019:6
/Applications/Racket
v5.0/collects/drracket/private/module-language-tools.rkt:58:6:
on-tab-change method in ...e-language-tools.rkt:49:4
/Applications/Racket v5.0/collects/drracket/private/tracing.rkt:168:6:
on-tab-change method in .../private/tracing.rkt:163:4
/Applications/Racket v5.0/collects/drracket/private/debug.rkt:1580:6:
on-tab-change method in ...et/private/debug.rkt:1506:4
/Applications/Racket v5.0/collects/drracket/private/unit.rkt:2847:8:
change-to-tab method in ...ket/private/unit.rkt:1419:6
/Applications/Racket v5.0/collects/drracket/private/unit.rkt:2817:10: core
/Applications/Racket v5.0/collects/racket/private/map.rkt:45:11: for-each
/Applications/Racket v5.0/collects/cosmonaut/tabs.rkt:26:6
/Applications/Racket
v5.0/collects/racket/private/class-internal.rkt:3596:0:
continue-make-super
/Applications/Racket v5.0/collects/gui-debugger/debug-tool.rkt:1048:8
/Applications/Racket
v5.0/collects/racket/private/class-internal.rkt:3596:0:
continue-make-super
/Applications/Racket v5.0/collects/macro-debugger/tool.rkt:118:6
...


--

#lang racket/gui
(require racket/class
         framework
         racket/unit
         racket/path
         drracket/tool)

(preferences:set-default
 'ProjectManager:tabs "/Users/spdegabrielle/tabs.sp"
 ; (path->string (build-path (find-system-path 'home-dir) "tabs.sp"))
 string?)

(provide tool@)
(define tool@
  (unit
    (import drracket:tool^)
    (export drracket:tool-exports^)
    (define (phase1) (void))
    (define (phase2) (void))
    ;
    ;    (define tab-mixin
    ;      (mixin ()()
    ;        (super-new)
    ;        ))
    (define (save/load-tabs-mixin super%)
      (class super%
        (inherit open-in-new-tab get-tabs)

        ;        ;; 'ProjectManager:tabs ; path to tabs file
        (field (saved-tabs-file (string->path "/Users/spdegabrielle/tabs.sp")))
                                 ;(preferences:get 'ProjectManager:tabs))))
        ;
        ;; save-tabs : out-file tabs -> void
        (define/private (save-tabs-file out-file tabs)
          (call-with-output-file out-file; saved-tabs-file-path
            (lambda (i) (write tabs i))
            #:exists 'replace))
        ;
        ;; each-tab -> list of files
        ;; return the paths for all tabs that have one
        (define/private (get-tab-files)
          (map path->string
               (filter (lambda (filename) filename)
                       (map
                        (λ (t) (send (send t get-defs) get-filename))
                        (get-tabs)))))
        ;
        (define (save-tabs-to-file-on-exit-callback)
          (save-tabs-file saved-tabs-file (get-tab-files)))

        ;
        (super-new)
        ;
        ;; reload-tab-from-file : in-file -> void
        (define/private (reload-my-tabs-from-file tabs-file)
          (let ((list-of-files (call-with-input-file tabs-file read)))
            (for-each (λ (f) (open-in-new-tab f)) list-of-files)))

        ;; get-tab-filename a-drscheme:unit:tab? -> (or/c path-string? false/c)
        ;; return #f if tab has no filename
        (define (get-tab-filename tab)
          (send (send tab get-defs) get-filename))

        (reload-my-tabs-from-file saved-tabs-file)

        (exit:insert-on-callback save-tabs-to-file-on-exit-callback)
        ))

    ;   (drracket:get/extend:extend-tab tab-mixin)
    (drracket:get/extend:extend-unit-frame save/load-tabs-mixin)
    ))
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