UIButton设置为圆形按钮并增加边框

UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];
btn.frame = CGRectMake(100, 100, 100, 100);

// 设置按钮四个圆角的半径，默认为0，这里取边长一半便是一个圆
btn.layer.cornerRadius = 50.0;
// 设置边框的宽度
btn.layer.borderWidth = 1.0;

CGColorSpaceRef spaceRef = CGColorSpaceCreateDeviceRGB();
CGColorRef colorRef = CGColorCreate(spaceRef, (CGFloat[]){255/255.0, 0/255.0, 0/255.0, 1});

// 设置边框的颜色
btn.layer.borderColor = colorRef;
btn.backgroundColor = [UIColor lightGrayColor];
[btn setTitle:@"Button" forState:UIControlStateNormal];