How can I refresh core plot without returning from a method?

Question

Hi. I have a cocoa interface that uses core plot. When I press a button in the interface, a plot is drawn. I wanted to create a sequence of graphs by calling the plotting method multiple times along with calls to sleep() in between. But it seems that even though the call to reload data is made that nothing happens until the function exits(only showing last graph as well). Now I know that CPAnimation exists but before I start using it I was wondering what it is that happens when the function exits that makes the graph refresh. Would I have to yield to the thread that takes care of the refreshing instead of using sleep?

Answer 1

Presumably, Core Plot (or your code) sets the view as needing display. That doesn't happen immediately; it happens when you return to the event loop.

Whenever you use sleep in a Mac OS X application, you kill a puppy. Use NSTimer instead. Have your timer callback method do the work required for one graph, and set whatever instance variables are necessary for your the method to know which graph it should draw, so that the method draws each graph in turn until it runs out of them.

Or, better yet, present a list of graphs that the user can choose from, instead of making the user watch all the graphs as a slide-show. (Unless an explicitly-labeled slide-show is what you're implementing.)

Answer 2

Peter has it right—the reload data method doesn't actually draw anything. The plot is marked as needing display and refreshed the next time the layers are drawn to the screen. If you use sleep, it never gets a chance to draw.

Also note that Core Plot is a fairly young project; CPAnimation and the related classes are stubs. They don't really do anything yet. :-)

Answer 3

Ok I figured out how. I called the reloadData method from a method in a separate thread (which always returns). This boiled down to calling reloadData from an IBAction and also with an NSTimer. Finally instead of using sleep I will use NSConditionLock coordinate the processing and the refreshing

Answer 4

Core Plot, like most Cocoa drawing frameworks, is lazy: it draws at the end of the run loop iteration. This is to ensure that things aren't drawn too often.

Rather than drawing immediately, the layers are marked as needing drawing.

As was pointed out by others, a better approach to sleeping is to use NSTimer to avoid blocking the run loop, or to use NSObject methods like performSelector:withObject:afterDelay: