级别： ★★☆☆☆
标签：「iOS颜色渐变」「CAGradientLayer渐变」「CAGradientLayer」
作者： Xs·H
审校： QiShare团队
在iOS 绘制渐变·基础篇的基础上，CAGradientLayer配合CAShapeLayer可以实现很多渐变效果。本文列举三个，并附上实现思路。
1、渐变色进度条
- 渐变色进度条实现效果
渐变色进度条
- 渐变色进度条实现代码
// 进度条view
UIView *progressView = [[UIView alloc] initWithFrame:CGRectMake(30.0, 100.0, self.view.bounds.size.width - 30.0 * 2, 5.0)];
progressView.center = (CGPoint){self.view.bounds.size.width / 2, self.view.bounds.size.height / 3};
progressView.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;
progressView.backgroundColor = [[UIColor lightGrayColor] colorWithAlphaComponent:.3];
progressView.layer.cornerRadius = progressView.bounds.size.height / 2;
progressView.layer.masksToBounds = YES;
[self.view addSubview:progressView];
// 渐变色layer
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = progressView.bounds;
gradientLayer.colors = @[(__bridge id)[[UIColor greenColor] colorWithAlphaComponent:1.0].CGColor,
(__bridge id)[[UIColor blueColor] colorWithAlphaComponent:1.].CGColor,
(__bridge id)[[UIColor purpleColor] colorWithAlphaComponent:1.0].CGColor,];
gradientLayer.startPoint = (CGPoint){.0};
gradientLayer.endPoint = (CGPoint){1.0};
[progressView.layer addSublayer:gradientLayer];
// mask layer
CALayer *maskLayer = [CALayer layer];
maskLayer.frame = (CGRect){.0, .0, .0, gradientLayer.bounds.size.height};
maskLayer.backgroundColor = [UIColor whiteColor].CGColor;
gradientLayer.mask = maskLayer;
// 设置变化规则
CGFloat deltaWidth = gradientLayer.bounds.size.width / 60;
[NSTimer scheduledTimerWithTimeInterval:.1 repeats:YES block:^(NSTimer * _Nonnull timer) {
CGRect rect = maskLayer.bounds;
rect.size.width += deltaWidth;
maskLayer.frame = rect;
if (gradientLayer.bounds.size.width - maskLayer.bounds.size.width < deltaWidth) {
[timer invalidate];
}
}];
- 渐变色进度条实现思路
1）创建progressView，设置浅灰色，切圆角，作为progress为0时的状态；
2）创建gradientLayer，设置渐变色，左右均匀渐变，覆盖到progressView.layer上面，作为progress为1时的状态；
3）创建maskLayer，设置非透明色，赋值给gradientLyaer.mask，作为progress变化时的状态。
4）定时改变maskLayer的width，通过maskLayer的width和gradientLayer重合部分来控制progress。
PS：
layer.mask与layer的非透明色重合部分才会被显示出来。
用同样的思路，也可以做出反向的进度条，效果如下：
渐变色进度条-反向
2、渐变色圆框
- 渐变色圆框实现效果
渐变色圆框
- 渐变色圆框实现代码
// 圆框所在区域View
UIView *arcView = [[UIView alloc] initWithFrame:CGRectMake(.0, .0, 300.0, 300.0)];
arcView.center = (CGPoint){self.view.bounds.size.width / 2, self.view.bounds.size.height / 3};
arcView.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;
[self.view addSubview:arcView];
// 渐变色 layer
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = arcView.bounds;
gradientLayer.colors = @[(__bridge id)[[UIColor redColor] colorWithAlphaComponent:1.0].CGColor,
(__bridge id)[[UIColor greenColor] colorWithAlphaComponent:1.0].CGColor,
(__bridge id)[[UIColor blueColor] colorWithAlphaComponent:1.0].CGColor];
gradientLayer.startPoint = CGPointMake(.0, .0);
gradientLayer.endPoint = CGPointMake(.0, 1.0);
[arcView.layer addSublayer:gradientLayer];
// 图形绘制 layer
CGFloat lineWidth = 10.0;
CGFloat rectSide = arcView.bounds.size.width - lineWidth;
UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:(CGRect){lineWidth / 2, lineWidth / 2, rectSide, rectSide}];
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = path.CGPath;
shapeLayer.fillColor = [UIColor clearColor].CGColor;
shapeLayer.strokeColor = [UIColor whiteColor].CGColor;
shapeLayer.lineWidth = lineWidth;
gradientLayer.mask = shapeLayer;
- 渐变色圆框实现思路
1）创建arcView，确定渐变色圆框所在的区域；
2）创建gradientLayer，设置渐变色，上下均匀渐变，覆盖到arcView.layer上面；
3）创建shapeLayer，设置fillColor为透明色，设置strokeColor为非透明色，设置合适的lineWidth；
4）创建bezierPath(path)，根据lineWidth设置绘制区域，赋值给shapeLayer.path；
5）将shapeLayer赋值给gradientLayer.mask，控制显示出的圆框区域；
PS：圆框绘制可以理解成用圆规画圆，
lineWidth表示圆规笔尖的宽度，rectSide表示笔尖中心放置的位置，strokerColor表示笔尖的颜色，fillColor表示闭合圆框内部的填充色。
3、渐变色弧段
- 渐变色弧段实现效果
渐变色弧段
- 渐变色弧段实现代码
// 弧段所在区域view
UIView *arcView = [[UIView alloc] initWithFrame:CGRectMake(.0, .0, 300.0, 300.0)];
arcView.center = (CGPoint){self.view.bounds.size.width / 2, self.view.bounds.size.height / 3};
arcView.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;
[self.view addSubview:arcView];
// 左侧渐变色 layer
CAGradientLayer *gradientLayerLeft = [CAGradientLayer layer];
gradientLayerLeft.frame = CGRectMake(.0, .0, arcView.bounds.size.width / 2, arcView.bounds.size.height);
gradientLayerLeft.colors = @[(__bridge id)[[UIColor yellowColor] colorWithAlphaComponent:1.0].CGColor,
(__bridge id)[[UIColor greenColor] colorWithAlphaComponent:1.0].CGColor];
gradientLayerLeft.locations = @[@(.0), @(.67)];
gradientLayerLeft.startPoint = CGPointMake(.0, .0);
gradientLayerLeft.endPoint = CGPointMake(.0, 1.0);
[arcView.layer addSublayer:gradientLayerLeft];
// 右侧渐变色 layer
CAGradientLayer *gradientLayerRight = [CAGradientLayer layer];
gradientLayerRight.frame = CGRectMake(arcView.bounds.size.width / 2.0, .0, arcView.bounds.size.width / 2, arcView.bounds.size.height);
gradientLayerRight.colors = @[(__bridge id)[[UIColor yellowColor] colorWithAlphaComponent:1.0].CGColor,
(__bridge id)[[UIColor redColor] colorWithAlphaComponent:1.0].CGColor];
gradientLayerRight.locations = @[@(.0), @(.67)];
gradientLayerRight.startPoint = CGPointMake(.0, .0);
gradientLayerRight.endPoint = CGPointMake(.0, 1.0);
[arcView.layer addSublayer:gradientLayerRight];
// 弧段绘制 layer
CGFloat lineWidth = 10.0;
CGFloat rectSide = arcView.bounds.size.width - lineWidth;
UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(arcView.bounds.size.width / 2, arcView.bounds.size.height / 2) radius:rectSide / 2 startAngle:-7.0 / 6 * M_PI endAngle:-11.0 / 6 * M_PI clockwise:YES];
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = path.CGPath;
shapeLayer.fillColor = [UIColor clearColor].CGColor;
shapeLayer.strokeColor = [UIColor whiteColor].CGColor;
shapeLayer.lineWidth = lineWidth;
shapeLayer.lineCap = @"round";
arcView.layer.mask = shapeLayer;
- 渐变色弧段实现思路
1）创建arcView，确定渐变色弧段所在的区域；
2）创建左侧的gradientLayer，设置渐变色，上下均匀渐变，覆盖到arcView.layer上面；
3）创建右侧的gradientLayer，设置渐变色，上下均匀渐变，覆盖到arcView.layer上面；
4）创建shapeLayer，设置fillColor为透明色，设置strokeColor为非透明色，设置合适的lineWidth；
4）创建bezierPath(path)，根据lineWidth设置绘制区域，赋值给shapeLayer.path；
5）将shapeLayer赋值给arcView.mask，控制显示出的弧段区域；
PS：贝塞尔曲线的的角度规则为：从圆心开始，水平向右的弧度为
0，顺时针弧度变大，逆时针弧度变小，水平向左为π。
以上渐变色绘制实例的源码可从工程QiGradientLayer中获取。
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