How can I scroll a UIView of indefinite size within a UIScrollView

Question

I'm trying to draw a graph that is indefinitely large horizontally, and the same height as the screen. I've added a UIScrollView, and a subclass of a UIView within it, which implements the -drawRect: method. In the simulator, everything works fine, but on the device, it can't seem to draw the graph after it reaches a certain size.

I'm already caching pretty much everything I can, and basically only calling CGContextAddLineToPoint in the -drawRect: section. I'm only drawing what's visible on the screen. I have a delegate to the UIScrollView which listens for -scrollViewDidScroll: which then tells the graph to redraw itself ([graphView setNeedsDisplay]).

I found one method that tells me to override the +layerClass method and return [CATiledLayer class]. This does allow the graph to actually draw on the device, but it functions very poorly. It's incredibly slow to actually draw, and the fade in that occurs is undesirable.

Any suggestions?

Answer 1

Well, here's my answer: I basically did something similar to how the UITableView works with cells: I have an NSMutableSet of GraphView objects which store unused graphs. When a section of the scroll view becomes visible, I take a graph view from that set (or make a new one if the set is empty). It already had a scrollX property to determine which part of it was supposed to draw. I set the scrollX property to the correct value and, instead of using the screen width, I gave it an arbitrary width to draw. When it goes out of the scroll view, it is removed from the UIScrollView and added to the set.

I wonder though if I really even need to remove them when they go outof the view? It may be prudent to try leaving them in and remove the ones not on screen only if I get a low memory warning? This might get rid of the pause whenever it needs to redraw a section of graph that hasn't changed.

My saving grace here was that my GraphView already was set up to draw only a portion of the graph. All I needed to do then was just make more than one of them.

Answer 2

I think this is a limitation of the iPhone graphics hardware. Through experimentation, I have seen that the iPhone will refuse to draw a frame that is bigger than 2000 pixels in either height or width. It probably has something to do with limited size for frame buffers in hardware.