XLCircleProgress 介绍
XLCircleProgress，是一个利用贝塞尔曲线实现的圆环进度指示器。
CGFloat circleWidth = self.view.bounds.size.width; _circle = [[XLCircleProgress alloc] initWithFrame:CGRectMake(0, 0, circleWidth, circleWidth)]; _circle.center = self.view.center; [self.view addSubview:_circle];