UIButton的阴影颜色和阴影偏移不显示

Question

影子不工作，为什么我写的UIBarButtonItem像，例如：？

UIImage *imageNomal  = [UIImage imageNamed:@"Back_A"]; 
UIImage *imageHight  = [UIImage imageNamed:@"Back_B"]; 
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom]; 
button.bounds = CGRectMake(0, 0, imageNomal.size.width, imageNomal.size.height+2); 
[button.layer setShadowColor:[[UIColor whiteColor] CGColor]]; 
[button.layer setShadowOffset:CGSizeMake(0, 2)]; 
[button setImage:imageNomal forState:UIControlStateNormal]; 
[button setImage:imageHight forState:UIControlStateHighlighted]; 
[button addTarget:nav action:@selector(backClick:) forControlEvents:UIControlEventTouchUpInside]; 
__autoreleasing UIBarButtonItem *barButtonItem = [[UIBarButtonItem alloc] initWithCustomView:button]; 

Answer 1

您需要设置shadowOpacity到的东西比0

较大