How to imitate the workflow view of Automator?

Question

I’m starting to develop my first full-blown Cocoa application containing a view which I would like to behave (and look) similar to Automator’s AMWorkflowView.

The basic features I’d like to achieve:

• Positioning of subviews
• Display of subviews in expanded / collapsed states
• Multiple selection
• Drag and drop

In order to get accustomed to Cocoa, I started with a custom NSView which mainly served as a container for the custom subviews and handled their positioning and multiple selection. The subviews are also subclasses of NSView, and contain a variable amount of views themselves, like buttons, labels and popup menus, and therefore can have different heights. This worked quite well, but before going on, I want to make sure to have everything neat and tidy according to the MVC pattern.

I suspect that there already is a class in Cocoa that facilitates the implementation of a view container, like maybe NSCollectionView. It seems that there is no (easy) way to display differently sized views in an NSCollectionView, though. Should I continue implementing my custom NSView (probably using an NSArrayController for selection and sorting support), or are there better ways to go?

Any help is much appreciated

Answer 1

Unfortunately the answer is you'll have to roll your own. NSCollectionView does not allow for variable-sized items (which also rules out expanded/collapsed states).

For a limited number of items, you can accomplish this rather easily (you just need a container view that arranges the subviews properly when asked to layout, then you need to make sure you re-layout when things change). For many subviews, however, you'll need to take care to be as efficient as possible. This can start with laying out as little as possible (only those "after" the resized view, for example) and get as complex as caching a visual representation of a prototype view, drawing the cached images (fast!) for all but the view being edited, and only using/positioning a "real" view for the view being edited.

Drag and drop works the same as it always has, but none of the above accounts for the pretty animation NSCollectionView gives you. :-) It's fast and beautifully-animated precisely because all the subviews are uniform (so the layout calculations are fast and simple). Once you add irregular sizes, the problem becomes significantly more complicated.

The bottom line: If you need variably-sized views, NSCollectionView will not work and you'll need to roll your own or find someone else's shared code, but performance and beautiful animation will not be easy.