Using lastObject to get dynamic content size of UIScrollView

UIScrollView *uiscrollview = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 320, 560)];

// add subview
[uiscrollview addSubview:[self addImage:UIViewContentModeScaleToFill :CGPointMake(20, 44) :CGSizeMake(280, 280)]];
[uiscrollview addSubview:[self addImage:UIViewContentModeScaleAspectFit :CGPointMake(20, 334) :CGSizeMake(280, 280)]];
[uiscrollview addSubview:[self addImage:UIViewContentModeScaleAspectFill :CGPointMake(20, 624) :CGSizeMake(280, 280)]];
[uiscrollview addSubview:[self addImage:UIViewContentModeTopLeft :CGPointMake(20, 914) :CGSizeMake(280, 280)]];

// get dynamic content size
UIView *lo = [uiscrollview.subviews lastObject];
NSInteger oy = lo.frame.origin.y;
NSInteger ht = lo.frame.size.height;
uiscrollview.contentSize = CGSizeMake(uiscrollview.frame.size.width, oy + ht);

[self.view addSubview:uiscrollview];