本文主要介紹一種繪制顏色漸變的進度圓環(huán). 先上效果圖:

實現(xiàn)思路:
CAShapeLayer+UIBezierPath+CAGradientLayer

1. UIBezierPath 用來繪制圓環(huán)路徑;
2. CAShapeLayer 根據(jù)UIBezierPath繪制的曲線路徑渲染出圖形, 利用GPU渲染節(jié)省內(nèi)存,提高性能;
3. CAGradientLayer 用來繪制顏色漸變的圖層, 最后添加到view的layer用來展示;

步驟:

1. 先創(chuàng)建一個UIView的子類CirlceView, 在其內(nèi)部實現(xiàn)圓環(huán)的繪制.

CircleView *circle = [[CircleView alloc] initWithFrame:CGRectMake(80, 100, 200, 200)];
circle.backgroundColor = [UIColor lightGrayColor];
[self.view addSubview:circle];

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2.繪制背景圓環(huán), 并將其添加到view的layer層上.

//創(chuàng)建背景圓環(huán)
CAShapeLayer *trackLayer = [CAShapeLayer layer];
trackLayer.frame = self.bounds;
//清空填充色
trackLayer.fillColor = [UIColor clearColor].CGColor;
//設(shè)置畫筆顏色 即圓環(huán)背景色
trackLayer.strokeColor =  [UIColor colorWithRed:170/255.0 green:210/255.0 blue:254/255.0 alpha:1].CGColor;
trackLayer.lineWidth = 20;
//設(shè)置畫筆路徑
UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(self.frame.size.width/2.0, self.frame.size.height/2.0) radius:self.frame.size.width/2.0 - 10 startAngle:- M_PI_2 endAngle:-M_PI_2 + M_PI * 2 clockwise:YES];
//path 決定layer將被渲染成何種形狀
trackLayer.path = path.CGPath;
[self.layer addSublayer:trackLayer];

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3. 使用CAGradientLayer 繪制漸變的背景色
由于CAShapeLayer不能順著弧線進行漸變只能指定兩個點之間進行漸變, 所以四種顏色的漸變只能是將view分成四個小的部分, 分別實現(xiàn)兩種顏色間的漸變. 最后在組合在一起, 形成四種顏色的漸變.

CGFloat width = rect.size.width;
CGFloat height = rect.size.height;

CALayer *gradientLayer = [CALayer layer];
gradientLayer.frame = self.bounds;

CAGradientLayer *gradientLayer1 = [CAGradientLayer layer];
gradientLayer1.frame = CGRectMake(width/2.0, 0, width/2.0,  height/2.0);
gradientLayer1.colors = @[(__bridge id)[UIColor redColor].CGColor, (__bridge id)[UIColor orangeColor].CGColor];
 //startPoint和endPoint屬性，他們決定了漸變的方向。這兩個參數(shù)是以單位坐標系進行的定義，所以左上角坐標是{0, 0}，右下角坐標是{1, 1}
//startPoint和pointEnd 分別指定顏色變換的起始位置和結(jié)束位置.
//當(dāng)開始和結(jié)束的點的x值相同時, 顏色漸變的方向為縱向變化
//當(dāng)開始和結(jié)束的點的y值相同時, 顏色漸變的方向為橫向變化
//其余的 顏色沿著對角線方向變化
gradientLayer1.startPoint = CGPointMake(0.2, 0);
gradientLayer1.endPoint = CGPointMake(0.8, 1);
[gradientLayer addSublayer:gradientLayer1];

CAGradientLayer *gradientLayer2 = [CAGradientLayer layer];
gradientLayer2.frame = CGRectMake(width/2.0, width/2.0, width/2.0,  height/2.0);
gradientLayer2.colors = @[(__bridge id)[UIColor orangeColor].CGColor, (__bridge id)[UIColor yellowColor].CGColor];
[gradientLayer2 setLocations:@[@0.3, @0.8,@1]];
gradientLayer2.startPoint = CGPointMake(0, 0);
gradientLayer2.endPoint = CGPointMake(0, 1);
[gradientLayer addSublayer:gradientLayer2];

CAGradientLayer *gradientLayer3 = [CAGradientLayer layer];
gradientLayer3.frame = CGRectMake(0, width/2.0, width/2.0,  height/2.0);
gradientLayer3.colors = @[(__bridge id)[UIColor yellowColor].CGColor, (__bridge id)[UIColor greenColor].CGColor];
gradientLayer3.startPoint = CGPointMake(0.5, 1);
gradientLayer3.endPoint = CGPointMake(0.5, 0);
[gradientLayer addSublayer:gradientLayer3];

CAGradientLayer *gradientLayer4 = [CAGradientLayer layer];
gradientLayer4.frame = CGRectMake(0, 0, width/2.0,  height/2.0);
gradientLayer4.colors = @[(__bridge id)[UIColor greenColor].CGColor, (__bridge id)[UIColor blueColor].CGColor];
gradientLayer4.startPoint = CGPointMake(0.5, 1);
gradientLayer4.endPoint = CGPointMake(0.5, 0);
[gradientLayer addSublayer:gradientLayer4];

[self.layer addSublayer:gradientLayer];

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4. 將顏色圖層切成圓環(huán)
@property (nonatomic, strong) CAShapeLayer *progressLayer;
_progressLayer = [CAShapeLayer layer];
_progressLayer.frame = self.bounds;
_progressLayer.fillColor = [UIColor clearColor].CGColor;
_progressLayer.strokeColor = [UIColor colorWithRed:170/255.0 green:210/255.0 blue:254/255.0 alpha:1].CGColor;
_progressLayer.lineWidth = 20;
_progressLayer.path = path.CGPath;
gradientLayer.mask = _progressLayer;

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5. 利用locations 屬性調(diào)整顏色空間
根據(jù)上面的運行結(jié)果可以看出底部的顏色交接的地方有顏色的斷層. 主要是第三部分底部的黃色區(qū)域較小導(dǎo)致的. 可以利用locations數(shù)組進行微調(diào).
默認情況下，這些顏色在空間上均勻地被渲染，但是我們可以用locations屬性來調(diào)整空間。locations屬性是一個浮點數(shù)值的數(shù)組(以NSNumber包裝)。這些浮點數(shù)定義了colors屬性中每個不同顏色的位置，同樣的，也是以單位坐標系進行標定。0.0代表著漸變的開始，1.0代表著結(jié)束。
[gradientLayer2 setLocations:@[@0.3, @0.8]];

   [gradientLayer3 setLocations:@[@0.2,@0.8]];

Paste_Image.png