How do I capture UIImage of complete contents of UITableView / UIScrollView and make it work on an ios device

Question

I am using this wonderfully elegant piece of code Getting a screenshot of a UIScrollView, including offscreen parts to capture the entire contents of a UITableView to be exported to a UIImage.

UIGraphicsBeginImageContextWithOptions(self.controller.tableView.contentSize, YES, 0);
{
    CGPoint savedContentOffset = self.controller.tableView.contentOffset;
    CGRect savedFrame = self.controller.tableView.frame;

    self.controller.tableView.contentOffset = CGPointZero;
    self.controller.tableView.frame = CGRectMake(0, 0, self.controller.tableView.contentSize.width, self.controller.tableView.contentSize.height);

    [self.controller.tableView.layer renderInContext: UIGraphicsGetCurrentContext()];
    image = UIGraphicsGetImageFromCurrentImageContext();

    self.controller.tableView.contentOffset = savedContentOffset;
    self.controller.tableView.frame = savedFrame;
}

UIGraphicsEndImageContext();

It works fantastically well in the simulator, however, when I run this code on an iOS device (iphone 4s) i get a whole leap of the following errors when this method is called:

[self.controller.tableView.layer renderInContext: UIGraphicsGetCurrentContext()];

Errors:

Error: CGContextTranslateCTM: invalid context 0x2924b0
Error: CGContextDrawImage: invalid context 0x2924b0
Error: CGContextRestoreGState: invalid context 0x2924b0
Error: CGContextSaveGState: invalid context 0x2924b0
Error: CGContextScaleCTM: invalid context 0x2924b0
Error: CGContextClipToRect: invalid context 0x2924b0
etc...

This code works well when the table views content size is within its bounds but as soon as it is greater than its bounds (even by 1 pixel) it goes into an endless loop of the above errors. But this only happens on the device. Not the simulator.

Any ideas?

Creese

Answer 1

It turns out that using the [UIImage ..] resizableImageWithCapInsets] method and applying it to the cell backgroundView and adjusting the frame causes all sorts of funky badness to happen on actual devices but not the simulator.

Reverting back to the deprecated [UIImage ..] stretchableImageWithLeftCapWidth: topCapHeight:] method solved it.

Creese

Spent a couple hours on this today. Thanks so much. Does anyone know if this issue been reported to Apple? Switching to a deprecated method seems like a poor long term solution. – Locoweed