iOS 8 Snapshotting a view that has not been rendered results in an empty snapshot

Question

I'm pretty sure this is just a bug in iOS 8.0. It's reproducible with the simplest of POC apps that does nothing more than attempt to present a UIImagePickerController like you're doing above. Furthermore, there's no alternative pattern to displaying the image picker/camera, to my knowledge. You can even download Apple's Using UIImagePickerController sample app, run it, and it will generate the same error out of the box.

That said, the functionality still works for me. Other than the warning/error, do you have issues with the functioning of your app?

I was struggling with this issue for several hours, i have read every relevant topic and found out that the error was caused because under the privacy settings of my device, the camera access to my app was blocked!!! I have never denied access to camera and i don't know how it was blocked but that was the problem!

I don't have enough reputation points to comment on @greg's answer above, so will add my observations here. I have a Swift project for both iPad and iPhone. I have a method inside my main view controller (relevant bit below). When I test this on a phone, everything works properly and no warnings are generated. When I run it on an iPad, everything works properly but I see the warning about snapshotting the view. The interesting bit, however, is that when I run on an iPad without using the popover controller, everything works properly with no warning. Unfortunately, Apple mandates that the image picker must be used within a popover on iPad, if the camera is not being used.

    dispatch_async(dispatch_get_main_queue(), {
        let imagePicker: UIImagePickerController = UIImagePickerController();
        imagePicker.sourceType = UIImagePickerControllerSourceType.SavedPhotosAlbum;
        imagePicker.mediaTypes = [kUTTypeImage];
        imagePicker.allowsEditing = false;
        imagePicker.delegate = self;

        if(UIDevice.currentDevice().userInterfaceIdiom == .Pad){ // on a tablet, the image picker is supposed to be in a popover
            let popRect: CGRect = buttonRect;
            let popover: UIPopoverController = UIPopoverController(contentViewController: imagePicker);
            popover.presentPopoverFromRect(popRect, inView: self.view, permittedArrowDirections: UIPopoverArrowDirection.Up, animated: true);
        }else{
            self.presentViewController(imagePicker, animated: true, completion: nil);
        }
    });

I ran into this after calling UIImagePickerController presentViewController: from the callback to a UIAlertView delegate. I solved the issue by pushing the presentViewController: call off the current execution trace using dispatch_async.

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
    dispatch_async(dispatch_get_main_queue(), ^{
        UIImagePickerController *imagePickerController = [[UIImagePickerController alloc] init];
        imagePickerController.delegate = self;

        if (buttonIndex == 1)
            imagePickerController.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        else
            imagePickerController.sourceType = UIImagePickerControllerSourceTypeCamera;

        [self presentViewController: imagePickerController
                           animated: YES
                         completion: nil];
    });
}

I had this issue when animating some views and the app would go into background mode and come back. I handled it by setting a flag isActive. I set it to NO in

- (void)applicationWillResignActive:(UIApplication *)application

and YES in

- (void)applicationDidBecomeActive:(UIApplication *)application

and animate or not animate my views accordingly. Took care of the issue.

I had this with an UIAlertControllerStyleActionSheet giving the user the option to take a photo with the camera or use one from library.

I tried a symbolic breakpoint on the error message

That showed me the error is produced by the intern use of a UICollectionView during presentation

[self presentViewController:alert animated:YES completion:nil];

I fixed this by explixitly setting the frame before presenting

[alert setPreferredContentSize: alert.view.frame.size];

Here is the complete methode that is working without the error

-(void)showImageSourceAlertFromSender:(id)sender{
UIButton *senderButton = (UIButton*)sender;
UIAlertController *alert = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
UIAlertAction *cameraAction = [UIAlertAction actionWithTitle:@"Camera" style:UIAlertActionStyleDefault
                                                     handler:^(UIAlertAction *action) {
                                                         [self takePhoto];
                                                     }];
UIAlertAction *libraryAction = [UIAlertAction actionWithTitle:@"Library" style:UIAlertActionStyleDefault
                                                      handler:^(UIAlertAction *action) {
                                                          [self selectPhotoFromLibraryFromSender:sender];
                                                      }];
[alert addAction:cameraAction];
[alert addAction:libraryAction];
alert.popoverPresentationController.delegate = self;
alert.popoverPresentationController.sourceRect = senderButton.frame;
alert.popoverPresentationController.sourceView = self.view;

[alert setPreferredContentSize: alert.view.frame.size];

[self presentViewController:alert animated:YES completion:^(){
}];}

You can silence the "Snapshotting a view" warning by referencing the view property before presenting the view controller. Doing so causes the view to load and allows iOS render it before taking the snapshot.

UIAlertController *controller = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
controller.modalPresentationStyle = UIModalPresentationPopover;
controller.popoverPresentationController.barButtonItem = (UIBarButtonItem *)sender;

... setup the UIAlertController ... 

[controller view]; // <--- Add to silence the warning.

[self presentViewController:controller animated:YES completion:nil];