如何将css方框阴影转换为IOS阴影

.box {
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

#import <QuartzCore/QuartzCore.h>

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
view.backgroundColor = [UIColor whiteColor];

CALayer *shadowLayer = view.layer;
shadowLayer.shadowColor = [UIColor blackColor].CGColor;
shadowLayer.shadowOffset = CGSizeMake(0, 2);
shadowLayer.shadowOpacity = 0.2;
shadowLayer.shadowRadius = 4;

[self.view addSubview:view];