Why does NSTableView use NSCell instead of NSView?

Question

This may be a general discussion instead of a real question. When I started using NSTableView and NSOutlineView, I thought : oh, a instance of NSView may do almost everything. So I return a NSView instance in my delegate and dataSource.

Of couse it did not work and I realized that NSTableView consitsts of instances of NSCell which inherits directly from NSObject.

I sensed that it may be important to understand why Cocoa constructed NSTableView based on NSCell but NSView. But few documents explain it clearly. Therefore I turn to Stackoverflow. Does anyone know that? Thank you at advance!

Answer 1

You can switch to a view based NSTableView or NSOutlineView in the inspector

The reason for a cell based cell would be if your only want to display a string. If you only want to display a string it would be a waste of resources to init a whole view to each cell. It is basically about memory control vs. what you need to display.

Answer 2

@d00dle's answer shows how to use an NSView backed table view, but it doesn't answer the question of why NSTableViews historically used NSCells in the first place.

The answer is that NSViews are heavy objects and expensive to manage. NSTableViews typically need many many rows and columns of "view-like" things, and if you naively added them all as actual NSViews, you can't maintain a responsive UI.

This is reflected in the trickiness Apple added to support NSView-backed table and outline views; it creates a limited number of NSViews and recycles them in clever ways to reduce the total number of NSViews in use at any given moment.