iOS之CAGradientLayer属性简介和使用

1、CAGradientLayer简介

　　CAGradientLayer用于制作背景图层的颜色渐变，也就是颜色梯度！相关属性简介：

#import <QuartzCore/CALayer.h>
#import <Foundation/NSArray.h>

NS_ASSUME_NONNULL_BEGIN

CA_CLASS_AVAILABLE (10.6, 3.0, 9.0, 2.0)
@interface CAGradientLayer : CALayer

//颜色数组 CGColor
@property(nullable, copy) NSArray *colors;

//颜色区间范围数组，范围是[0-1]并且是递增
@property(nullable, copy) NSArray<NSNumber *> *locations;

//开始坐标和结束坐标 范围（0-1）
//默认值（0.5，0.0） （0.5，1.0）
@property CGPoint startPoint;
@property CGPoint endPoint;

//绘制类型，目前只有一个参数也是默认值kCAGradientLayerAxial
@property(copy) NSString *type;

@end

/** `type' values. **/

CA_EXTERN NSString * const kCAGradientLayerAxial
CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);

NS_ASSUME_NONNULL_END

2、CAGradientLayer的简单使用：

    self.showView = [[UIView alloc] initWithFrame:CGRectMake(100,(CScreenHeight-200)/2,CScreenWidth-200,200)];
    CAGradientLayer *layer = [CAGradientLayer layer];
    layer.frame = CGRectMake(0,0,CScreenWidth-200,200);
    layer.colors = @[(id)UIColor.redColor.CGColor,
                     (id)UIColor.whiteColor.CGColor,
                     (id)UIColor.redColor.CGColor];
    layer.locations = @[@(-0.2),@(-0.1),@0];
    layer.startPoint = CGPointMake(0, 0);
    layer.endPoint = CGPointMake(1, 1);
    layer.type = kCAGradientLayerAxial;
    [self.showView.layer addSublayer:layer];
    self.layer = layer;
    self.showView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:self.showView];
    self.waterTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(waterAction) userInfo:nil repeats:YES];

- (void)waterAction{
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"locations"];
    animation.fromValue = @[@(-0.3), @(-0.2), @(0)];
    animation.toValue   = @[@(1.0), @(1.2), @(1.3)];
    animation.duration  = 1;
    [self.layer addAnimation:animation forKey:nil];
}

效果图