IOS: How to make a shadow for UIView on 4 side (top,right,bottom and left)

Only following code will do the job for your requirement, You don't need to create UIBezierPath for shadow path.

// *** Set masks bounds to NO to display shadow visible ***
self.avatarImageView.layer.masksToBounds = NO;
// *** Set light gray color as shown in sample ***
self.avatarImageView.layer.shadowColor = [UIColor lightGrayColor].CGColor;
// *** *** Use following to add Shadow top, left ***
self.avatarImageView.layer.shadowOffset = CGSizeMake(-5.0f, -5.0f);

// *** Use following to add Shadow bottom, right ***
//self.avatarImageView.layer.shadowOffset = CGSizeMake(5.0f, 5.0f);

// *** Use following to add Shadow top, left, bottom, right ***
// avatarImageView.layer.shadowOffset = CGSizeZero;
// avatarImageView.layer.shadowRadius = 5.0f;

// *** Set shadowOpacity to full (1) ***
self.avatarImageView.layer.shadowOpacity = 1.0f;

Without using UIBezierPath, CGSize.zero is the key here

yourView.layer.masksToBounds = false
yourView?.layer.shadowColor = UIColor.red.cgColor
yourView?.layer.shadowOffset =  CGSize.zero
yourView?.layer.shadowOpacity = 0.5
yourView?.layer.shadowRadius = 4

Like this:

float shadowSize = 10.0f;
UIBezierPath *shadowPath = [UIBezierPath bezierPathWithRect:CGRectMake(self.avatarImageView.frame.origin.x - shadowSize / 2,
                                                                       self.avatarImageView.frame.origin.y - shadowSize / 2,
                                                                       self.avatarImageView.frame.size.width + shadowSize,
                                                                       self.avatarImageView.frame.size.height + shadowSize)];
self.avatarImageView.layer.masksToBounds = NO;
self.avatarImageView.layer.shadowColor = [UIColor blackColor].CGColor;
self.avatarImageView.layer.shadowOffset = CGSizeMake(0.0f, 0.0f);
self.avatarImageView.layer.shadowOpacity = 0.8f;
self.avatarImageView.layer.shadowPath = shadowPath.CGPath;

Swift 3 version:

    let shadowSize : CGFloat = 5.0
    let shadowPath = UIBezierPath(rect: CGRect(x: -shadowSize / 2,
                                               y: -shadowSize / 2,
                                               width: self.avatarImageView.frame.size.width + shadowSize,
                                               height: self.avatarImageView.frame.size.height + shadowSize))
    self.avatarImageView.layer.masksToBounds = false
    self.avatarImageView.layer.shadowColor = UIColor.black.cgColor
    self.avatarImageView.layer.shadowOffset = CGSize(width: 0.0, height: 0.0)
    self.avatarImageView.layer.shadowOpacity = 0.5
    self.avatarImageView.layer.shadowPath = shadowPath.cgPath

Little less code for swift 3:

    view.layer.shadowColor = UIColor.black.cgColor
    view.layer.shadowOpacity = 0.7
    view.layer.shadowOffset = CGSize.zero
    view.layer.shadowRadius = 4
    view.layer.shadowPath = UIBezierPath(rect: planView.bounds).cgPath