How to add a gradient to a scrollview? - iphone

Question

I am trying to add a bunch of gradients to different UIScrollView's and UITableView's. The most common example of how to achieve this that i have come across is from Matt Galagher's awesome blog where he posted an example of how to use gradients here:
http://cocoawithlove.com/2009/08/adding-shadow-effects-to-uitableview.html
My question though is what advantages/benefits do you gain by inserting the gradient in the layoutSubviews method vs setting up the gradient in the viewDidLoad method? I realize that by goin the viewDidLoad route you would have to update the view manually when the orientation changes but it would seem from a performance standpoint that this method would only be called once when the view loads and then again when the orientation changes. In contrast the layoutSubviews method gets called everytime time the view changes which in the case of a scrollview/tableview is a lot!
//
// Construct the origin shadow if needed
//
if (!originShadow)
{
originShadow = [self shadowAsInverse:NO];
[self.layer insertSublayer:originShadow atIndex:0];
}
else if (![[self.layer.sublayers objectAtIndex:0] isEqual:originShadow])
{
[self.layer insertSublayer:originShadow atIndex:0];
}
[CATransaction begin];
[CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
//
// Stretch and place the origin shadow
//
CGRect originShadowFrame = originShadow.frame;
originShadowFrame.size.width = self.frame.size.width;
originShadowFrame.origin.y = self.contentOffset.y;
originShadow.frame = originShadowFrame;
[CATransaction commit];
He also seems to be resizing the frame everytime the method is called? Wouldnt it be better to initialize and size the gradient in the viewDidLoad method and then do any resizing when/if the orientation changes?
Pretty sure im missing something here so any clarification would be appreciated.
Thx

Answer 1

I wouldn't create the gradient in layoutSubviews. Layout subviews might get called more often than is optimal for this kind of drawing. By doing something CPU intensive in layoutSubviews, like creating a gradient, you might adversely impact performance.
Instead, what I would do is put your gradient on a subview and then add your subview into your scrollview (viewDidLoad, init, or awakeFromNib is good for this) and let it handle it's drawing automatically. Then, in layoutSubviews, adjust the layout of your subview, and let it handle figuring out what portions of the view need to be redrawn to update things.