Re: [wxhaskell-users] Creating an new attribute

[Jeremy O'D. <jer...@gm...>]

Hi,

On 28 February 2012 03:28, Alexander McPhail <
has...@gm...> wrote:

> Hi,
>
> Using GTK, the following works
>
> <code>
>
> -- | create a new 'Figure' plot
> --     click on the window to save
> plotNew :: FigureHandle -> IO DrawingArea
> plotNew f = do
>    canvas <- drawingAreaNew
>
>    set canvas [maybeFigure := (Just f)]
>
>    return canvas
>
>
> -----------------------------------------------------------------------------
>
> -- | the figure attribute
> figure :: Attr DrawingArea FigureState
> figure = newAttr getFigure setFigure
>    where getFigure o = do
>                        Just f <- get o maybeFigure
>                        readMVar f
>          setFigure o f = set o [maybeFigure :~> (\(Just h) -> do
>                                                               modifyMVar_
> h (\_ -> return f)
>                                                               return $
> Just h)]
>
>
> -----------------------------------------------------------------------------
>
> maybeFigure :: Attr DrawingArea (Maybe FigureHandle)
> maybeFigure = unsafePerformIO $ objectCreateAttribute
> {-# NOINLINE maybeFigure #-}
>
>
> -----------------------------------------------------------------------------
>
> </code>
>
> I am attempting to port this code to WxHaskell but can not see how to
> create a new attribute for the `FigureHandle`.
>
> This is the code I have so far
>
> type FigureHandle = MVar FigureState
>
>
> -----------------------------------------------------------------------------
> -- | create a new 'Figure' plot
> --     click on the window to save
> plot ::  Frame () -> FigureHandle -> IO (Panel ())
> plot fr f = do
>   p <- panel fr [figure := f]
>   set p [on paint := paintFigure p]
>   return p
>
> paintFigure :: Panel () -> DC a -> Rect -> IO ()
>
> -- | the figure attribute
> figure :: Attr (Panel a) FigureHandle
> figure = newAttr "figure" getFigure setFigure
>    where getFigure o = do
>            readMVar figureHandle
>          setFigure o f = do
>            modifyMVar_ figureHandle (\_ -> return f)
>

You may find this entry from my blog helpful:
http://wewantarock.wordpress.com/2010/01/11/custom-controls-in-wxhaskell-part-3/

I think you cannot create an attribute for FigureHandle. Attributes in
wxHaskell are typed on the control to which they apply, for example (taken
from the blog) if you have a DiffViewer control, then to create a diffFiles
attribute which sets the files to be compared has the type signature below

> diffFiles :: Attr (DiffViewer a) (FilePath, FilePath)
> diffFiles = newAttr "diffFiles" dvGetFiles dvSetFiles
>     where
>     dvGetFiles win = {- Code follows... -}
>     dvSetFiles win (txt1, txt2) = {- Code follows -}

You can just as easily create a new attribute for an existing control. In
this case, I think that what you need is much closer to the code you have
for GTK than what you have shown for wxHaskell.

Hope this helps - I don't have a Gtk2Hs install to let me check they types
of your working code, I'm afraid, so there is a bit of guesswork on my side.

Best regards
Jeremy