shadowColor 图片阴影 iOS

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor= [UIColor yellowColor];

UIButton *btn = [[UIButton alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
[btn setTitle:@"asdsdfa" forState:UIControlStateNormal];
[btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[btn setBackgroundImage:[UIImage imageNamed:@"11111"] forState:UIControlStateNormal];
//加阴影
btn.layer.shadowColor = [UIColor redColor].CGColor;//shadowColor阴影颜色
btn.layer.shadowOffset = CGSizeMake(4,4);//shadowOffset阴影偏移,x向右偏移4，y向下偏移4，默认(0, -3),这个跟shadowRadius配合使用
btn.layer.shadowOpacity = 0.8;//阴影透明度，默认0
btn.layer.shadowRadius = 4;//阴影半径，默认3
[self.view addSubview:btn];
}