snapshotView of UIView render/draw in context with nothing

Question

I'm trying to render/draw the snapshotView of a UIView in contex to get a UIImage.then set it as a CAlayer.contents. I try this method to get snapshotView:

snapshotViewAfterScreenUpdates:

then convert UIView to UIImage:

UIGraphicsBeginImageContext(view.bounds.size);
[view.layer renderInContext:UIGraphicsGetCurrentContext()];
//I'm trying this method too
[view drawViewHierarchyInRect:view.bounds afterScreenUpdates:NO];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

the problem is I'm using the code above, but I get a empty image.

In Apple's doc, `snapshotViewAfterScreenUpdates ` can't render in context. If snap image needed, try `[window.layer.presentationLayer drawViewHierarchyInRect. window.bounds afterScreenUpdates:NO]` — ooOlly, Mar 02 '17 at 06:44
`presentationLayer` will copy layer object that represents the state of the layer as it currently appears onscreen. — ooOlly, Mar 02 '17 at 06:46

score 8 · Accepted Answer · answered Mar 15 '15 at 13:50

8

If you need a snapshot UIImage in the first place just use the method in your second code block. Create a UIView's category like

@implementation UIView (takeSnapshot)

- (UIImage *)takeASnapshot {
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, [UIScreen mainScreen].scale);

    [self drawViewHierarchyInRect:self.bounds afterScreenUpdates:YES];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

@end

That's enough. You don't need snapshot a view and convert it to a image. In your case this process might cause the problem

answered Mar 15 '15 at 13:50

dopcn

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thanks,this works for me.I fix my project with some code changing,but I really want to know what happen in my situation. – ooOlly Mar 16 '15 at 06:52
3

Apple 'doc: **If you want to apply a graphical effect, such as blur, to a snapshot, use the drawViewHierarchyInRect:afterScreenUpdates: method instead.** – ooOlly Mar 02 '17 at 06:51

score 6 · Answer 2 · answered Jun 13 '18 at 08:29

Had a similar issue when building interactive animations with floating snapshots. Here what we did:

UIView extension:

extension UIView {

   public func snapshot(scale: CGFloat = 0, isOpaque: Bool = false, afterScreenUpdates: Bool = true) -> UIImage? {
      UIGraphicsBeginImageContextWithOptions(bounds.size, isOpaque, scale)
      drawHierarchy(in: bounds, afterScreenUpdates: afterScreenUpdates)
      let image = UIGraphicsGetImageFromCurrentImageContext()
      UIGraphicsEndImageContext()
      return image
   }


   public enum CASnapshotLayer: Int {
      case `default`, presentation, model
   }

   /// The method drawViewHierarchyInRect:afterScreenUpdates: performs its operations on the GPU as much as possible
   /// In comparison, the method renderInContext: performs its operations inside of your app’s address space and does
   /// not use the GPU based process for performing the work.
   /// https://stackoverflow.com/a/25704861/1418981
   public func caSnapshot(scale: CGFloat = 0, isOpaque: Bool = false,
                          layer layerToUse: CASnapshotLayer = .default) -> UIImage? {
      var isSuccess = false
      UIGraphicsBeginImageContextWithOptions(bounds.size, isOpaque, scale)
      if let context = UIGraphicsGetCurrentContext() {
         isSuccess = true
         switch layerToUse {
         case .default:
            layer.render(in: context)
         case .model:
            layer.model().render(in: context)
         case .presentation:
            layer.presentation()?.render(in: context)
         }
      }
      let image = UIGraphicsGetImageFromCurrentImageContext()
      UIGraphicsEndImageContext()
      return isSuccess ? image : nil
   }
}

Usage example (inside interactive animation):

private func makeSnapshot(view: UIView, snapshotLayer: UIView.CASnapshotLayer) -> UIView? {
   // There is 3 ways for taking snapshot:
   // 1. Replicate view: `view.snapshotView(afterScreenUpdates: true)`
   // 2. Draw Hierarchy: `view.drawHierarchy(in: bounds, afterScreenUpdates: true)`
   // 3. Render Layer: `layer.render(in: context)`
   //
   // Only #3 is working reliable during UINavigation controller animated transitions.
   // For modally presented UI also trick by combining #1 and #2 seems works.
   // I.e. `view.snapshotView(afterScreenUpdates: true).snapshot()`
   //
   // If this call causes error listed below, then this indicate that something wrong with one of the views layout.
   // [Snapshotting] View (_UIReplicantView) drawing with afterScreenUpdates:YES inside CoreAnimation commit is not supported.
   // See also: https://stackoverflow.com/a/29676207/1418981
   if let image = view.caSnapshot(layer: snapshotLayer) {
      let imageView = ImageView(image: image)
      imageView.clipsToBounds = true
      imageView.contentMode = .scaleAspectFit
      shapshots[view] = image
      return imageView
   }
   return nil
}

Wow, what a great solution. Tested and works on Swift 5 – Johno2110 Sep 22 '19 at 07:54 — Johno2110, Sep 22 '19 at 07:54
For me not working when controller modally presented – V.V.V Jun 10 '20 at 10:42 — V.V.V, Jun 10 '20 at 10:42

snapshotView of UIView render/draw in context with nothing

2 Answers2