UIImage from a UIView created with snapshotViewAfterScreenUpdates:

Question

Is it possible to get a UIImage from a UIView created with snapshotViewAfterScreenUpdates?

A UIView returned from snapshotViewAfterScreenUpdates looks fine when added as a subview, but the following produces a black image:

UIView *snapshotView = [someView snapshotViewAfterScreenUpdates:YES]; 
UIImage *snapshotImage = [self imageFromView:snapshotView]; 

- (UIImage *)imageFromView:(UIView *)view
{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, YES, 0.0);
    // [view.layer renderInContext:UIGraphicsGetCurrentContext()]; // <- same result...
    [view drawViewHierarchyInRect:view.bounds afterScreenUpdates:NO];
    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return img;
}

It is of course possible to get the image without relying on snapshotViewAfterScreenUpdates:

UIImage *snapshotImage = [self imageFromView:someView];

Unfortunately, when capturing a complex view, drawViewHierarchyInRect can't match the speed of snapshotViewAfterScreenUpdates. I was hoping that it would be faster to get the UIImage from a view created by snapshotViewAfterScreenUpdates, is this possible?

carton · Accepted Answer · 2013-11-25T21:47:20.593

21

The answer seems to be NO and Apple's documentation implicitly confirms this:

If you want to apply a graphical effect, such as blur, to a snapshot, use the drawViewHierarchyInRect:afterScreenUpdates: method instead.

It's worth noting that the Implementing Engaging UI on iOS session from WWDC13 lists snapshotViewAfterScreenUpdates as the fastest method, but uses drawViewHierarchyInRect in the example code.

edited Nov 25 '13 at 21:47

answered Nov 25 '13 at 21:41

carton

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I think the reason this is not working is that the view returned by snapshot is actually NOT a full fledged view. If you step through the debugger, you will see that it's type is '_UIReplicantView'. This makes me think that it is just an optimized copy of the other view and doesn't have the same 'layer' characteristics of a 'full' UIView... – MobileVet Nov 26 '13 at 16:27
1

Thanks @MobileVet, that's good to know. Still frustrating that there's no way to get the pixels from a feature that is all about quick screen capture... – carton Nov 27 '13 at 20:55
1

Apple confirms that this is not possible. See: http://www.raywenderlich.com/forums/viewtopic.php?f=37&t=8993&start=10 – Carlos Guzman Jun 11 '14 at 06:48
@CarlosGuzman thanks for adding that link, it contains some helpful explanations. – carton Jun 11 '14 at 20:24
Very frustrating. drawViewHierarchyInRect is too slow and uses too much CPU. You'd think there'd be a simple way to get an OpenGL texture or at least a CVPixelBufferRef from a view since it's all OpenGL underneath anyway... – jjxtra Feb 04 '15 at 04:56

UIImage from a UIView created with snapshotViewAfterScreenUpdates:

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