[wxhaskell-users] Creating an new attribute

[Alexander M. <has...@gm...>]

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)

-----------------------------------------------------------------------------

I looked in the CustomControl.hs example, which uses a pre-existing
attribute and does not create a new one in the way that the call to
`objectCreateAttribute` does with GTK.

Thanks,

Vivian


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