最近项目需要，想做一个渐变色的刻度盘，圆形按钮滑动控制，所以 用oc写了一下，代码没附上，想看代码可以私信联系，效果如下图。

部分代码

self.drawCenter = CGPointMake(self.frame.size.width / 2.0, self.frame.size.height / 2.0);self.radius = self.circleRadius;self.circleStartPoint = CGPointMake(self.drawCenter.x, self.drawCenter.y - self.circleRadius);CGContextRef ctx = UIGraphicsGetCurrentContext();//圆形的背景颜色CGContextSetStrokeColorWithColor(ctx, self.backgroundTintColor.CGColor);CGContextSetLineWidth(ctx, self.circleBorderWidth);CGContextAddArc(ctx, self.drawCenter.x, self.drawCenter.y, self.radius, 0, 2 * M_PI, 0);CGContextDrawPath(ctx, kCGPathStroke);//加载的进度UIBezierPath *loadPath = [UIBezierPath bezierPath];CGFloat loadStart = -M_PI_2;CGFloat loadCurre = loadStart + 2 * M_PI * self.loadProgress;[loadPath addArcWithCenter:self.drawCenterradius:self.radiusstartAngle:loadStartendAngle:loadCurreclockwise:YES];CGContextSaveGState(ctx);CGContextSetShouldAntialias(ctx, YES);CGContextSetLineWidth(ctx, self.circleBorderWidth);CGContextSetStrokeColorWithColor(ctx, self.maximumTrackTintColor.CGColor);CGContextAddPath(ctx, loadPath.CGPath);CGContextDrawPath(ctx, kCGPathStroke);CGContextRestoreGState(ctx);//起始位置做圆滑处理CGContextSaveGState(ctx);CGContextSetShouldAntialias(ctx, YES);CGContextSetFillColorWithColor(ctx, self.minimumTrackTintColor.CGColor);CGContextAddArc(ctx, self.circleStartPoint.x, self.circleStartPoint.y, self.circleBorderWidth / 2.0, 0, M_PI * 2, 0);CGContextDrawPath(ctx, kCGPathFill);CGContextRestoreGState(ctx);//valueUIBezierPath *circlePath = [UIBezierPath bezierPath];CGFloat originstart = -M_PI_2;CGFloat currentOrigin = originstart + 2 * M_PI * self.value;[circlePath addArcWithCenter:self.drawCenterradius:self.radiusstartAngle:originstartendAngle:currentOriginclockwise:YES];CGContextSaveGState(ctx);CGContextSetShouldAntialias(ctx, YES);CGContextSetLineWidth(ctx, self.circleBorderWidth);CGContextSetStrokeColorWithColor(ctx, self.minimumTrackTintColor.CGColor);CGContextAddPath(ctx, circlePath.CGPath);CGContextDrawPath(ctx, kCGPathStroke);CGContextRestoreGState(ctx);/** 计算移动点的位置* alpha = 移动点相对于起始点顺时针扫过的角度(弧度)* x = r * sin(alpha) + 圆心的x坐标, sin在0-PI之间为正，PI-2*PI之间为负* y 可以通过r * cos(alpha) + 圆心的y坐标来计算。* 不过我这里用了另外一个比较投机的方法，先算出亮点连线在y轴上投影的长度，然后根据移动点在y轴上相对于圆心的位置将这个绝对长度a和圆心y坐标相加减。*/double alpha = self.value * 2 * M_PI;double x = self.radius * sin(alpha) + self.drawCenter.x;double y = sqrt(self.radius * self.radius - pow((self.drawCenter.x - x), 2)) + self.drawCenter.y;double a = y - self.drawCenter.y;if (self.value <= 0.25 || self.value > 0.75) {y = self.drawCenter.y - a;}self.lastPoint = CGPointMake(x, y);self.thumbView.center = self.lastPoint;