自定义圆形（或者有倒角）的button

UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];

btn.layer.cornerRadius = 25;//半径、长宽一半

btn.layer.borderWidth = 1.0;

btn.layer.borderColor = [UIColor clearColor].CGColor;

btn.clipsToBounds = TRUE;//去除边界

btn.backgroundColor = [UIColor redColor];

btn.frame = CGRectMake(100, 100, 50, 50);//button基础必须是正方形，才有可能倒角成圆形

[self.view addSubview:btn];