Take a snapshot of a hidden UIView

问题:

I'm trying to take a snapshot of a hidden view but am running into several issues. If I try unhiding it quickly, taking a snapshot, and then rehiding it, I sometimes get a quick flicker on the screen that is pretty jarring.

toCollectionViewCell.hidden = NO;
UIView *toPlaceHolderSnapshot = [toCollectionViewCell resizableSnapshotViewFromRect:toCollectionViewCell.bounds afterScreenUpdates:YES withCapInsets:UIEdgeInsetsZero];
toCollectionViewCell.hidden = YES;

I'm pretty sure the flicker is caused by the afterScreenUpdates:YES, but I can't imagine that is intended behavior.

I've also tried moving the cell/view off screen instead of hiding it, but I can't be certain when that cell might be reloaded and therefore moved back into its place prematurely.

Is there a way to take a snapshot of a hidden view or a more clever way to achieve this? I need this functionality during a custom transition animation where I am pulling a collection view cell out of the collection view and then returning it back into place on dismiss. I am taking snapshots of the before/after state and then transitioning between the two during the animation.

Thanks!

回答1:

Add an extra container view to your view hierarchy. Hiding the container will have the same visual effect, but you'll be able to snapshot the content of a container with ease.

回答2:

I've also tried moving the cell/view off screen instead of hiding it, but I can't be certain when that cell might be reloaded and therefore moved back into its place prematurely.

This approach is probably the simplest. As long as all of your work is done on the main thread, the cell won't move during your snapshot.

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You could also try archiving and then unarchiving the view (to essentially copy it):

id copyOfView = 
[NSKeyedUnarchiver unarchiveObjectWithData:[NSKeyedArchiver archivedDataWithRootObject:originalView]];
UIView *viewCopy = (UIView *)copyOfView;
viewCopy.hidden = NO;

(All views in the hierarchy will need to conform to the NSCoding protocol.)

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Finally, you could draw your cell to a UIImage, and then display it in a UIImageView. Sample code here.