I am one of the developers on the ActionStep project (http://osflash.org/projects/actionstep), which is an OSS implementation of Cocoa in ActionScript 2.0 (Flash).
Now this may seem like a completely elementary question, but for I’m having the hardest time figuring out how highlighting and states interact during the drawing of NSButtonCell. Would someone be so kind as to describe the big picture surrounding these two concepts, and how they affect drawing. Just pick a button type…let’s say NSSwitchButton.
Thank you, Scott Hyndman
(And if you’re interested in looking at some our code, here’s the repo address http://svn1.cvsdude.com/osflash/actionstep/trunk/src/org/actionstep/)
Highlight and state are two abstract pieces of metadata that are given a visual interpretation using the showsStateBy and highlightsBy masks.
State can be on, off, or mixed. All buttons change state when they are clicked, but most buttons do not display a visual difference when on, due to the contents of the showsStateBy mask.
Highlight is just on or off. Unfortunately it means slightly different things for different kinds of cells. For a button, highlighted is pretty much synonymous with “pressed”. All buttons turn highlighted when pressed, but they show the highlight differently following the highlightsBy mask.
The visual interpretation mask options are NSPushInCellMask, NSContentsCellMask, NSChangeGrayCellMask and NSChangeBackgroundCellMask. Unfortunately, these date back to the NeXTStep operating system and make less sense now then they did then.
NSPushInCellMask is easy. Look pushed.
NSContentsCellMask means “use alternate title and image”. So if the showsStateBy mask contains NSContentsCellMask, then an on button will display its alternate image. If the highlightsBy mask contains NSContentsCellMask, then a pressed button cell will display its alternate image.
NSChangeGrayCellMask and NSChangeBackgroundCellMask are interpreted pretty loosely these days as “look different”. They’re effectively similar to NSPushInCellMask.
IB doesn’t directly expose the highlightsBy and showsStateBy masks. It lets you call setButtonType:, which is a convenience method for setting up collections of button attributes. For most button types, the only attributes set are the highlightsBy mask and showsStateBy mask.
A lot of this stuff is the way it is for compatibility with older code.
Checkboxes are also a funky case. Most other complex button styles are exposed as ‘bezel types’, where the bezel drawing is a monolithic drawBezel method (which means it can have an arbitrary number of different looks). Checkboxes are borderless (== no bezel) buttons, which draw the checkbox as images. Buuut there are many different images, while NSButtonCell can only be configured with two (image, alternateImage).
But, at a very high level it’s the same. state gives on, off or mixed, highlighted gives pressed or unpressed.
 For most cells, setting the highlight to YES is something done by, say, NSTableView for cells that are in a selected row. NSTableView has to know that NSButtonCell interprets highlight as pressed, and thus not set it in this circumstance.
Thank you. I think that’s all I need to continue.
*  For most cells, setting the highlight to YES is something done by, say, NSTableView for cells that are in a selected row. NSTableView has to know that NSButtonCell interprets highlight as pressed, and thus not set it in this circumstance. *
Wow, that seems like very poor design. I actually just finished writing the table view and that’s why I’m getting into this business. Let’s hope I can figure out a workaround without special cases all over the place.