Downloading tiles for CATiledLayer with NSURLConnection

I'm looking into the Apple ScrollViewSuite and the Photoscroller, and I wonder how to implement a CATiledLayer when downloading the tiles through an NSURLConnection: how do I notify drawRect: that a specific tile has been downloaded and how do I keep track of the r开发者_JAVA百科ects and contexts associated with each tile?

Regards Fredrik

When you finish downloading, cache the results, and then call setNeedsDisplayInRect: with the tile's rect. It will call drawLayer:inContext: again, and you can then draw the cached results.

I thing there are just no way for doing this because it is supposed to work to other way around. Tiles are rendered in separated thread and thus you could start downloading the tile from the drawLayer:InContext: method. Of course don't forget to implement caching for the downloaded tiles otherwise you will kill both your app and your invoice :-)

There's no way to get the necessary information out of the tiled layer. I'm currently simply invalidating/redrawing the layer once every few seconds to get some kind of "eventual consistency". That is, at some point in time I expect all visible tiles to have been loaded and cached (by my own controller). The redraw will then simply render all tiles using images from my cache.

For that to work, you need to be able to calculate the set of visible tiles and (re)download them if they're not cached. This approach has the huge benefit of allowing me to cancel connections for tiles that are no longer visible. And it allows the map to, eventually, recover from connection/server errors etcetera.

The tiled layer would need to export a lot of internals if you wanted to get away from this 'polling' approach, like which tiles it has cached and which it is currently interested in.