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];}