ios - 如何在UIButton里面获取阴影

Question

使用下面的代码为 UIButton 的外部添加阴影。但是我怎样才能在按钮内部获得阴影

button.imageView.layer.cornerRadius = 7.0f;
button.layer.shadowRadius = 3.0f;
button.layer.shadowColor = [UIColor blackColor].CGColor;
button.layer.shadowOffset = CGSizeMake(0.0f, 1.0f);
button.layer.shadowOpacity = 0.5f;
button.layer.masksToBounds = NO;

Answer 1

   #define kDEFAULT_SHADOW_COLOR [UIColor lightGrayColor]   
   UIColor *color = [kDEFAULT_SHADOW_COLOR colorWithAlphaComponent:0.3f];
        NSArray *colorsArray = @[(id)[color CGColor], (id)[[UIColor clearColor] CGColor]];
        CGFloat yOffset = 0.0f;
        CGFloat leftHeight = button.bounds.size.height;
        CAGradientLayer *shadow;
        shadow = [CAGradientLayer layer];
        shadow.colors = colorsArray;
        shadow.frame = CGRectMake(0, yOffset, 5.0, leftHeight);
        shadow.startPoint = CGPointMake(0.0, 0.5);
        shadow.endPoint = CGPointMake(1.0, 0.5);
        [button.layer insertSublayer:shadow atIndex:0];