Drawing incrementally in a UIView (iPhone)

Question

As far as I have understood so far, every time I draw something in the drawRect: of a UIView, the whole context is erased and then redrawn.

So I have to do something

Answer 1

If you are able to cache the drawing as an image, you can take advantage of UIView's CoreAnimation backing. This will be much faster than using Quartz, as Quartz does its drawing in software.

- (CGImageRef)cachedImage {
    /// Draw to an image, return that
}
- (void)refreshCache {
    myView.layer.contents = [self cachedImage];
}
- (void)actionThatChangesWhatNeedsToBeDrawn {
    [self refreshCache];
}