總結iOS實現漸變顏色的三種方法

2020-07-26 03:09:08

字體：大中小

來源：轉載

供稿：網友

在iOS開發過程中有的時候會需要用到漸變的顏色，這篇文章總結了三種方法來實現，有需要的朋友們下面來一起看看吧。

一、CAGradientLayer實現漸變

CAGradientLayer是CALayer的一個特殊子類，用于生成顏色漸變的圖層，使用較為方便

下面介紹下它的相關屬性：

colors 漸變的顏色

locations 漸變顏色的分割點

startPoint&endPoint 顏色漸變的方向，范圍在(0,0)與(1.0,1.0)之間，如(0,0)(1.0,0)代表水平方向漸變,(0,0)(0,1.0)代表豎直方向漸變

 CAGradientLayer *gradientLayer = [CAGradientLayer layer]; gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor, (__bridge id)[UIColor yellowColor].CGColor, (__bridge id)[UIColor blueColor].CGColor]; gradientLayer.locations = @[@0.3, @0.5, @1.0]; gradientLayer.startPoint = CGPointMake(0, 0); gradientLayer.endPoint = CGPointMake(1.0, 0); gradientLayer.frame = CGRectMake(0, 100, 300, 100); [self.view.layer addSublayer:gradientLayer];

CAGradientLayer實現漸變標間簡單直觀，但存在一定的局限性，比如無法自定義整個漸變區域的形狀，如環形、曲線形的漸變。

二、Core Graphics相關方法實現漸變

iOS Core Graphics中有兩個方法用于繪制漸變顏色，CGContextDrawLinearGradient可以用于生成線性漸變，CGContextDrawRadialGradient用于生成圓半徑方向顏色漸變。函數可以自定義path，無論是什么形狀都可以，原理都是用來做Clip，所以需要在CGContextClip函數前調用CGContextAddPath函數把CGPathRef加入到Context中。
另外一個需要注意的地方是漸變的方向，方向是由兩個點控制的，點的單位就是坐標。因此需要正確從CGPathRef中找到正確的點，方法當然有很多種看具體實現，本例中，我就是簡單得通過調用CGPathGetBoundingBox函數，返回CGPathRef的矩形區域，然后根據這個矩形取兩個點，讀者可以根據自行需求修改具體代碼。

1-> 線性漸變

- (void)drawLinearGradient:(CGContextRef)context  path:(CGPathRef)path startColor:(CGColorRef)startColor  endColor:(CGColorRef)endColor{ CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGFloat locations[] = { 0.0, 1.0 }; NSArray *colors = @[(__bridge id) startColor, (__bridge id) endColor]; CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations); CGRect pathRect = CGPathGetBoundingBox(path); //具體方向可根據需求修改 CGPoint startPoint = CGPointMake(CGRectGetMinX(pathRect), CGRectGetMidY(pathRect)); CGPoint endPoint = CGPointMake(CGRectGetMaxX(pathRect), CGRectGetMidY(pathRect)); CGContextSaveGState(context); CGContextAddPath(context, path); CGContextClip(context); CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0); CGContextRestoreGState(context); CGGradientRelease(gradient); CGColorSpaceRelease(colorSpace);}- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. //創建CGContextRef UIGraphicsBeginImageContext(self.view.bounds.size); CGContextRef gc = UIGraphicsGetCurrentContext(); //創建CGMutablePathRef CGMutablePathRef path = CGPathCreateMutable(); //繪制Path CGRect rect = CGRectMake(0, 100, 300, 200); CGPathMoveToPoint(path, NULL, CGRectGetMinX(rect), CGRectGetMinY(rect)); CGPathAddLineToPoint(path, NULL, CGRectGetMidX(rect), CGRectGetMaxY(rect)); CGPathAddLineToPoint(path, NULL, CGRectGetWidth(rect), CGRectGetMaxY(rect)); CGPathCloseSubpath(path); //繪制漸變 [self drawLinearGradient:gc path:path startColor:[UIColor greenColor].CGColor endColor:[UIColor redColor].CGColor]; //注意釋放CGMutablePathRef CGPathRelease(path); //從Context中獲取圖像，并顯示在界面上 UIImage *img = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); UIImageView *imgView = [[UIImageView alloc] initWithImage:img]; [self.view addSubview:imgView];}

2-> 圓半徑方向漸變

- (void)drawRadialGradient:(CGContextRef)context  path:(CGPathRef)path startColor:(CGColorRef)startColor  endColor:(CGColorRef)endColor{ CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGFloat locations[] = { 0.0, 1.0 }; NSArray *colors = @[(__bridge id) startColor, (__bridge id) endColor]; CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations); CGRect pathRect = CGPathGetBoundingBox(path); CGPoint center = CGPointMake(CGRectGetMidX(pathRect), CGRectGetMidY(pathRect)); CGFloat radius = MAX(pathRect.size.width / 2.0, pathRect.size.height / 2.0) * sqrt(2); CGContextSaveGState(context); CGContextAddPath(context, path); CGContextEOClip(context); CGContextDrawRadialGradient(context, gradient, center, 0, center, radius, 0); CGContextRestoreGState(context); CGGradientRelease(gradient); CGColorSpaceRelease(colorSpace);}- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. //創建CGContextRef UIGraphicsBeginImageContext(self.view.bounds.size); CGContextRef gc = UIGraphicsGetCurrentContext(); //創建CGMutablePathRef CGMutablePathRef path = CGPathCreateMutable(); //繪制Path CGRect rect = CGRectMake(0, 100, 300, 200); CGPathMoveToPoint(path, NULL, CGRectGetMinX(rect), CGRectGetMinY(rect)); CGPathAddLineToPoint(path, NULL, CGRectGetMidX(rect), CGRectGetMaxY(rect)); CGPathAddLineToPoint(path, NULL, CGRectGetWidth(rect), CGRectGetMaxY(rect)); CGPathAddLineToPoint(path, NULL, CGRectGetWidth(rect), CGRectGetMinY(rect)); CGPathCloseSubpath(path); //繪制漸變 [self drawRadialGradient:gc path:path startColor:[UIColor greenColor].CGColor endColor:[UIColor redColor].CGColor]; //注意釋放CGMutablePathRef CGPathRelease(path); //從Context中獲取圖像，并顯示在界面上 UIImage *img = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); UIImageView *imgView = [[UIImageView alloc] initWithImage:img]; [self.view addSubview:imgView];}

三、以CAShapeLayer作為layer的mask屬性

CALayer的mask屬性可以作為遮罩讓layer顯示mask遮住(非透明)的部分；CAShapeLayer為CALayer的子類，通過path屬性可以生成不同的形狀，將CAShapeLayer對象用作layer的mask屬性的話，就可以生成不同形狀的圖層。

故生成顏色漸變有以下幾個步驟：

1、生成一個imageView(也可以為layer)，image的屬性為顏色漸變的圖片

2、生成一個CAShapeLayer對象，根據path屬性指定所需的形狀

3、將CAShapeLayer對象賦值給imageView的mask屬性

- (void)viewDidLoad{ [super viewDidLoad]; [self.view addSubview:self.firstCircle]; _firstCircle.frame = CGRectMake(0, 0, 200, 200); _firstCircle.center = CGPointMake(CGRectGetWidth(self.view.bounds) / 2.0, CGRectGetHeight(self.view.bounds) / 2.0); CGFloat firsCircleWidth = 5; self.firstCircleShapeLayer = [self generateShapeLayerWithLineWidth:firsCircleWidth]; _firstCircleShapeLayer.path = [self generateBezierPathWithCenter:CGPointMake(100, 100) radius:100].CGPath; _firstCircle.layer.mask = _firstCircleShapeLayer;} - (CAShapeLayer *)generateShapeLayerWithLineWidth:(CGFloat)lineWidth{ CAShapeLayer *waveline = [CAShapeLayer layer]; waveline.lineCap = kCALineCapButt; waveline.lineJoin = kCALineJoinRound; waveline.strokeColor = [UIColor redColor].CGColor; waveline.fillColor = [[UIColor clearColor] CGColor]; waveline.lineWidth = lineWidth; waveline.backgroundColor = [UIColor clearColor].CGColor; return waveline;}- (UIBezierPath *)generateBezierPathWithCenter:(CGPoint)center radius:(CGFloat)radius{ UIBezierPath *circlePath = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:0 endAngle:2*M_PI clockwise:NO]; return circlePath;}- (UIImageView *)firstCircle{ if (!_firstCircle) { self.firstCircle = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"circleBackground"]]; _firstCircle.layer.masksToBounds = YES; _firstCircle.alpha = 1.0; } return _firstCircle;}