Re: [hoc-users] Information on how to build a custom NSView subclass

[David C. <dw...@dw...>]

Joe wrote:

> I am trying to create a custom NSView subclass that, specifically one
> that overrides drawRect. What I am having a problem with is
> understanding how to override this function and how to actually get
> some custom drawing done. Actually, I;m not even sure if my class is
> being instantiated. I slapped a view into the ExpressionParser window,
> gave it a custom class with the same name as my class (which would
> normally be all I would need to do in Cocoa).

Joe,

Here's the source for a more complex view that I wrote in Haskell.  I  
can't remember if this compiles/works correctly (it was working at  
one point, but I started tinkering more), but it should give you  
something to go on as far as showing how to declare the draw_rect  
function appropriately.

Of particular note, I believe that I had to export the info_drawRect  
in the $(exportClass) directive in order for the Cocoa system to be  
able to call the haskellized replacement function.

(Also a style note, I was experimenting with some utility functions  
which use unsafePerformIO; said usage is not recommended... :-D)   
Additional disclaimer: this code was written about a year ago, so I'm  
sure there are general improvements which could be made in general.

I might make the following changes to your view, just to see if it  
gives you what you are expecting:

---
{-# OPTIONS -fglasgow-exts -fth #-}

module EPView where

import Cocoa
import AppKit.NSView as NSView hiding (print)

$(declareClass "EPView" "NSView")

$(exportClass "EPView" "ev_"
   [
    InstanceMethod info_drawRect
   ]
  )

obj #. var = obj # getIVar var

ev_drawRect rect self = do
     r <- self # NSView.bounds  -- proper instance selection.
     _NSColor # blackColor >>= set -- class selector
     nsRectFill r
     return ()
---

Regards,

David Christensen