Creating a blurring overlay view

Question

In the Music app of the new iOS, we can see an album cover behind a view that blurs it.

How can something like that be accomplished? I've read the documentation, but did not find anything there.

Answer 1

An important supplement to @Joey's answer

This applies to a situation where you want to present a blurred-background UIViewController with UINavigationController.

// suppose you've done blur effect with your presented view controller
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController];

// this is very important, if you don't do this, the blur effect will darken after view did appeared
// the reason is that you actually present navigation controller, not presented controller
// please note it's "OverFullScreen", not "OverCurrentContext"
nav.modalPresentationStyle = UIModalPresentationOverFullScreen;

UIViewController *presentedViewController = [[UIViewController alloc] init]; 
// the presented view controller's modalPresentationStyle is "OverCurrentContext"
presentedViewController.modalPresentationStyle = UIModalPresentationOverCurrentContext;

[presentingViewController presentViewController:nav animated:YES completion:nil];

Enjoy!

Answer 2

I don't think I'm allowed to post the code, but the above post mentioning the WWDC sample code is correct. Here is the link: https://developer.apple.com/downloads/index.action?name=WWDC%202013

The file you're looking for is the category on UIImage, and the method is applyLightEffect.

As I noted above in a comment, the Apple Blur has saturation and other things going on besides blur. A simple blur will not do... if you are looking to emulate their style.

Answer 3

Accepted answer is correct but there's an important step missing here, in case this view - for which you want blurred background - is presented using

[self presentViewController:vc animated:YES completion:nil]

By default, this will negate the blur as UIKit removes the presenter's view, which you are actually blurring. To avoid that removal, add this line before the previous one

vc.modalPresentationStyle = UIModalPresentationOverFullScreen;

Or use other Over styles.

Answer 4

Custom blur scale

You can try UIVisualEffectView with custom setting as -

class BlurViewController: UIViewController {
    private let blurEffect = (NSClassFromString("_UICustomBlurEffect") as! UIBlurEffect.Type).init()

    override func viewDidLoad() {
        super.viewDidLoad()
        let blurView = UIVisualEffectView(frame: UIScreen.main.bounds)
        blurEffect.setValue(1, forKeyPath: "blurRadius")
        blurView.effect = blurEffect
        view.addSubview(blurView)
    }   
}

Output:- for blurEffect.setValue(1... & blurEffect.setValue(2..

Answer 5

You can use UIVisualEffectView to achieve this effect. This is a native API that has been fine-tuned for performance and great battery life, plus it's easy to implement.

Swift:

//only apply the blur if the user hasn't disabled transparency effects
if !UIAccessibilityIsReduceTransparencyEnabled() {
    view.backgroundColor = .clear

    let blurEffect = UIBlurEffect(style: .dark)
    let blurEffectView = UIVisualEffectView(effect: blurEffect)
    //always fill the view
    blurEffectView.frame = self.view.bounds
    blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

    view.addSubview(blurEffectView) //if you have more UIViews, use an insertSubview API to place it where needed
} else {
    view.backgroundColor = .black
}

Objective-C:

//only apply the blur if the user hasn't disabled transparency effects
if (!UIAccessibilityIsReduceTransparencyEnabled()) {
    self.view.backgroundColor = [UIColor clearColor];

    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
    UIVisualEffectView *blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    //always fill the view
    blurEffectView.frame = self.view.bounds;
    blurEffectView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

    [self.view addSubview:blurEffectView]; //if you have more UIViews, use an insertSubview API to place it where needed
} else {
    self.view.backgroundColor = [UIColor blackColor];
}

If you are presenting this view controller modally to blur the underlying content, you'll need to set the modal presentation style to Over Current Context and set the background color to clear to ensure the underlying view controller will remain visible once this is presented overtop.

Answer 6

I decided to post a written Objective-C version from the accepted answer just to provide more options in this question..

- (UIView *)applyBlurToView:(UIView *)view withEffectStyle:(UIBlurEffectStyle)style andConstraints:(BOOL)addConstraints
{
  //only apply the blur if the user hasn't disabled transparency effects
  if(!UIAccessibilityIsReduceTransparencyEnabled())
  {
    UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:style];
    UIVisualEffectView *blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
    blurEffectView.frame = view.bounds;

    [view addSubview:blurEffectView];

    if(addConstraints)
    {
      //add auto layout constraints so that the blur fills the screen upon rotating device
      [blurEffectView setTranslatesAutoresizingMaskIntoConstraints:NO];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeTop
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeTop
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeBottom
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeBottom
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeLeading
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeLeading
                                                      multiplier:1
                                                        constant:0]];

      [view addConstraint:[NSLayoutConstraint constraintWithItem:blurEffectView
                                                       attribute:NSLayoutAttributeTrailing
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:view
                                                       attribute:NSLayoutAttributeTrailing
                                                      multiplier:1
                                                        constant:0]];
    }
  }
  else
  {
    view.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.7];
  }

  return view;
}

The constraints could be removed if you want incase if you only support portrait mode or I just add a flag to this function to use them or not..