draw(_ rect: CGRect) not drawing above certain size

Question

I have a custom UIView subclass inside a UIScrollView that (among other things) overrides

override var intrinsicContentSize: CGSize {
    get {
        ...
    }
}

and (minimal example):

override func draw(_ rect: CGRect) {
    print(rect)
    UIColor.white.set() // it has a dark background
    UIBezierPath(rect: CGRect(x: 100, y: 100, width: 10, height: 10)).stroke()
}

Drawing works fine for “smaller” sizes of the view, but above a certain limit nothing draws anymore.

It renders fine for the rects

(0.0, 0.0, 79.5, 7458.5)
(0.0, 0.0, 228.5, 7458.5)
(0.0, 0.0, 149.0, 7738.0)
(0.0, 0.0, 429.0, 7738.0)

But fails for the rects

(0.0, 0.0, 89.5, 8381.0)
(0.0, 0.0, 257.0, 8381.0)

There is no error message or warning. Nothing that would let me know what fails and why. The UIScrollView is still scrollable. Its contents are just empty.

This is happening in a simulated 5th generation iPad and the simulated iPad Pro 9.7".

Hans Hans · Accepted Answer · 2019-06-18T08:31:54

The problem is that draw is only meant as custom drawing for small views and not huge canvases. However I think this point of failure should be documented somewhere. Making the canvas even larger will result in a ignoring bogus layer size warning.

To solve this problem one should either consider

not using draw
using a UITableView or a UICollectionView to load and unload the huge layer bit by bit.

draw(_ rect: CGRect) not drawing above certain size

1 Answers