Drawing in a nested UIView - iphone

Question

I am trying to make a drawing application following this tutorial: http://www.effectiveui.com/blog/2011/12/02/how-to-build-a-simple-painting-app-for-ios/, and then I tried to make it such that I don't only draw on the entire screen, I only draw on a UIView that is inside of another UIView. (What I call a nested UIView)
My code is currently on github: https://github.com/sammy0025/SimplePaint
The only parts I tweaked with the original code from the tutorial is to change some class prefix names, enabled ARC so no deallocs, used storyboards (which works fine with the original code from the tutorial), and change this code in the main view controller implementation file (SPViewController.m):
-(void)viewDidLoad
{
[super viewDidLoad];
nestedView.backgroundColor=[UIColor colorWithWhite:0 alpha:0]; //This is to make the nested view transparent
SPView *paint = [[SPView alloc] initWithFrame:nestedView.bounds]; //original code is SPView *paint=[[SPView alloc] initWithFrame:self.view.bounds];
[nestedView addSubview:paint]; //original code is [self.view addSubview:paint];
}
My question is how do I make sure that I only draw inside the nested UIView?

Answer 1

Add clipping to your sub view. E.g. self.bounds would cover the whole area of a view.
UIBezierPath *p = [UIBezierPath bezierPathWithRect:self.bounds];
[p addClip];
I believe clipping for a view should be based on bounds initially and that you may shrink it by adding an new clipping. But there might be a difference between iOS and OS X here.

Answer 2

Rather than using an SPView inside a nested view, consider just changing the frame of the SPView to match what you want. This should solve your problem of only allowing drawing within a given rect.
I think you're seeing issues because of your storyboard configuration. I dont know much about storyboard, but I was able to get this to work programmatically by throwing out storyboard's view and building my own in viewDidAppear.
-(void)viewDidAppear:(BOOL)animated{
UIView *newView = [[UIView alloc] initWithFrame:self.view.bounds];
newView.backgroundColor = [UIColor greenColor];
SPView *newPaint = [[SPView alloc] initWithFrame:CGRectInset(self.view.bounds, 40,40)];
[newView addSubview:newPaint];
self.view = newView;
}