概念
- 1，CAGradientLayer用于处理渐变色的层结构
- 2，CAGradientLayer的渐变色可以做隐式动画
- 3，大部分情况下，CAGradientLayer时和CAShapeLayer配合使用的。关于CAShapeLayer可以看我的这篇博客
基于CAShapeLayer和贝塞尔曲线的圆形进度条动画【原创】 - 4，CAGradientLayer可以用作PNG的遮罩效果
关于CAGradientLayer的坐标系统
- 为什么要提到CAGradientLayer的坐标系统呢？因为渐变色的作用范围，变化梯度的方向，颜色变换的作用点都和CAGradientLayer的坐标系统有关
CAGradientLayer坐标图
根据上图的坐标，设定好起点和终点，渐变色的方向就会根据起点指向终点的方向来渐变了。
1，CAGradientLayer的坐标系统是从（0，0）到（1，1）绘制的矩形
2，CAGradientLayer的frame值的size不为正方形的话，坐标系统会被拉伸
3，CAGradientLayer的startPoint和endPoint会直接决定颜色的绘制方向
4，CAGradientLayer的颜色分割点时以0到1的比例来计算的
下面直接上代码，里面的注视都写好了。就不一一解释
- 方法1(定时器渐变)
#import "ViewController.h"
@interface ViewController ()
@property (strong, nonatomic) CAGradientLayer *gradientLayer;
@property (strong, nonatomic) NSTimer *timer;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
//初始化imageView
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image"]];
imageView.frame = CGRectMake(0, 0, self.view.bounds.size.width, 200);
imageView.center = self.view.center;
[self.view addSubview:imageView];
//初始化渐变层
self.gradientLayer = [CAGradientLayer layer];
self.gradientLayer.frame = imageView.bounds;
[imageView.layer addSublayer:self.gradientLayer];
//设置渐变颜色方向
self.gradientLayer.startPoint = CGPointMake(0, 0);
self.gradientLayer.endPoint = CGPointMake(0, 1);
//设定颜色组
self.gradientLayer.colors = @[(__bridge id)[UIColor clearColor].CGColor,
(__bridge id)[UIColor purpleColor].CGColor];
//设定颜色分割点
self.gradientLayer.locations = @[@(0.5f) ,@(1.0f)];
//定时器
self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0f
target:self
selector:@selector(TimerEvent)
userInfo:nil
repeats:YES];
}
- (void)TimerEvent
{
//定时改变颜色
self.gradientLayer.colors = @[(__bridge id)[UIColor clearColor].CGColor,
(__bridge id)[UIColor colorWithRed:arc4random() % 255 / 255.0
green:arc4random() % 255 / 255.0
blue:arc4random() % 255 / 255.0
alpha:1.0].CGColor];
//定时改变分割点
self.gradientLayer.locations = @[@(arc4random() % 10 / 10.0f), @(1.0f)];
}
@end
- 封装方法(类似支付宝)
//color gradient layer
- (void) insertColorGradient {
UIColor *colorOne = [UIColor colorWithRed:(255/255.0) green:(255/255.0) blue:(255/255.0) alpha:1.0];
UIColor *colorTwo = [UIColor colorWithRed:(33/255.0) green:(33/255.0) blue:(33/255.0) alpha:1.0];
NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, colorTwo.CGColor, nil nil];
NSNumber *stopOne = [NSNumber numberWithFloat:0.0];
NSNumber *stopTwo = [NSNumber numberWithFloat:1.0];
NSArray *locations = [NSArray arrayWithObjects:stopOne, stopTwo, nil nil];
CAGradientLayer *headerLayer = [CAGradientLayer layer];
headerLayer.colors = colors;
headerLayer.locations = locations;
headerLayer.frame = self.bounds;
[self.layer insertSublayer:headerLayer above:0];
}
- 封装方法3
//Transparent Gradient Layer
- (void) insertTransparentGradient {
UIColor *colorOne = [UIColor colorWithRed:(33/255.0) green:(33/255.0) blue:(33/255.0) alpha:0.0];
UIColor *colorTwo = [UIColor colorWithRed:(33/255.0) green:(33/255.0) blue:(33/255.0) alpha:1.0];
//
NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, colorTwo.CGColor, nil nil];
NSNumber *stopOne = [NSNumber numberWithFloat:0.0];
NSNumber *stopTwo = [NSNumber numberWithFloat:1.0];
NSArray *locations = [NSArray arrayWithObjects:stopOne, stopTwo, nil nil];
//crate gradient layer
//初始化渐变层
CAGradientLayer *headerLayer = [CAGradientLayer layer];
headerLayer.colors = colors;
headerLayer.locations = locations;
headerLayer.frame = self.bounds;
[self.layer insertSublayer:headerLayer atIndex:0];
}
