UIButton阴影不显示，代码如下

[zengjinzong]

//代码示例
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(10,500, 300, 50);
button.backgroundColor = UIColor.redColor;

button.cornerRadius = 3;
button.shadowRadius = 3;
button.shadowColor = UIColor.blackColor;
button.shadowOffset = CGSizeMake(3, 3);
button.shadowOpacity = 0.3;
[self.view addSubview:button];