CODEWITHSUNDEEP
cocoamacosnsview
ryyst
ryyst

Reputation: 9801

Cocoa - efficient view drawing

in my program, I'm implementing a custom view, a bit like a table view. To do so, I have subclassed NSView. Now my question is, what's the most efficient way to draw all the table view cells. Should I just use NSViews or possibly something else, like CALayers?

Thanks!

P.S.: This is on Mac OS X, not on iOS.

Upvotes: 0

Views: 718

Answers (1)

Joshua Nozzi
Joshua Nozzi

Reputation: 61228

Based on your question and comment, I propose two alternatives:

NSCollectionView / NSCollectionViewItem - This is useful only if all of your "cells" (instances of your prototype view) are the same dimensions. That is, you can't have one that's wider or taller than the others (or narrower or shorter). This is highly efficient and a ready part of AppKit. Even with a single column and n rows, it works like a charm.

Roll Your Own - This is harder but gives you flexibility. Much like NSCollectionView / NSCollectionViewItem, you'd have a view that serves as the container and you'd ideally have a view you reuse to draw the various "items" it's showing. Using the same view to set its represented object and "stamp" it into place (pose it and draw it), you can roll through your entire collection in one go then use that same view as the live, active view for whatever selected, focused item you have. Even faster: roll through and cache the images and sizes of each item with your reusable item view and draw all from the cache except the selected item (which would use a live, real view posed in its proper location, updating the cached image of itself as its contents change for when it's not selected). Faster still: 1 live view and 1 "for caching" view, and draw only the computed rects of the cached images that intersect the visible rect (sans the "live" / selected view). Note: the caching will have to be re-done each time the container's frame's width changes, since presumably shrinking horizontally means all items grow vertically. If you can, take advantage of NSOperation / NSOperationQueue to handle the caching in the background, only flagging for re-display when all cached items 0 - n (where n is the highest-indexed item intersecting the visible rect) are available.

I use something very close to the latter in one of my own applications, where the "item" is an entry with varying-length text. I don't employ all the tactics I mentioned in my own solution but most and the performance increase is very satisfying. :-)

Hope this helps.

Upvotes: 1

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