A custom background for a modal VC and rotation - ios

Question

I've implemented a custom (blurred) background for a modal view controller on iPad. Here's how I do it: in the presented VC's viewWillShow: I take a snapshot image of the presenting VC's view, blur it, and add a UIImage view on top of the presenting VC. This works well.
However, when I rotate the device while the modal is showing, the blurred image gets out of sync with the view controller it represents. The image gets stretched to fill the screen, but the view controller doesn't resize its views the same way. So when the modal is dismissed and the blur goes away, the transition looks bad.
I've tried taking another snapshot in didRotateFromInterfaceOrientation:, and replacing the blurred image, but that didn't work.
Any advice on how to solve this?
UPDATE: a sample project
My code (in the modal view controller):
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[self drawBackgroundBlurView];
}
- (void)drawBackgroundBlurView
{
if(_blurModalBackground) {
[_backgroundBlurView removeFromSuperview];
CGRect backgroundFrame = self.presentingViewController.view.bounds;
_backgroundBlurView = [[UIImageView alloc] initWithFrame:backgroundFrame];
_backgroundBlurView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
[_backgroundBlurView setImage:[STSUtils imageByBlurringView:self.presentingViewController.view]];
[self.presentingViewController.view addSubview:_backgroundBlurView];
}
}
Utils code
+ (UIImage *)imageByBlurringView:(UIView *)view
{
UIWindow *window = [[[UIApplication sharedApplication] windows] lastObject];
BOOL isPortrait = (UIInterfaceOrientationIsPortrait([[UIApplication sharedApplication] statusBarOrientation]));
CGRect frame;
if(isPortrait) {
frame = CGRectMake(view.frame.origin.x, view.frame.origin.y, view.frame.size.height, view.frame.size.width);
}
else {
frame = CGRectMake(view.frame.origin.x, view.frame.origin.y, view.frame.size.width, view.frame.size.height);
}
UIGraphicsBeginImageContextWithOptions(frame.size, NO, window.screen.scale);
[view drawViewHierarchyInRect:frame afterScreenUpdates:NO];
// Get the snapshot
UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
// Apply blur
UIColor *tintColor = [UIColor colorWithWhite:1.0 alpha:0.3];
UIImage *blurredSnapshotImage = [snapshotImage applyBlurWithRadius:8
tintColor:tintColor
saturationDeltaFactor:1.8
maskImage:nil];
UIGraphicsEndImageContext();
return blurredSnapshotImage;
}

Answer 1

I coded a simple example that takes a screenshot from presentingViewController and sets it as background image. Here is the implementaion of my modal view controller. And it works well (both on viewWillAppear and handles rotation properly). Could you please also post STSUtils code?
#import "ScreenshoterViewController.h"
#interface ScreenshoterViewController ()
#property (weak, nonatomic) IBOutlet UIImageView *imageView;
- (IBAction)buttonBackPressed;
#end
#implementation ScreenshoterViewController
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self updateImage];
}
- (void)updateImage
{
UIGraphicsBeginImageContext(self.view.bounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[self.presentingViewController.view.layer renderInContext:context];
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
self.imageView.image = img;
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation
{
[self updateImage];
}
- (IBAction)buttonBackPressed {
[self dismissViewControllerAnimated:YES
completion:NULL];
}
#end
Update
In your utils code just replace this
[view drawViewHierarchyInRect:frame afterScreenUpdates:NO];
with this
[view drawViewHierarchyInRect:frame afterScreenUpdates:YES];
From apple docs:
afterUpdates A Boolean value that indicates whether the snapshot
should be rendered after recent changes have been incorporated.
Specify the value NO if you want to render a snapshot in the view
hierarchy’s current state, which might not include recent changes.
So you were taking screenshot that did not included latest changes in the view.