CAGradientLayer处理颜色渐变效果

1、这个类很简单，下面简单介绍

/* CoreAnimation - CAGradientLayer.h

Copyright (c) 2008-2015, Apple Inc.
All rights reserved. */

/* The gradient layer draws a color gradient over its background color,
* filling the shape of the layer (i.e. including rounded corners). */

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

NS_ASSUME_NONNULL_BEGIN

@interface CAGradientLayer : CALayer

/* The array of CGColorRef objects defining the color of each gradient
* stop. Defaults to nil. Animatable. */

//这个数组里面保存了用于渐变的颜色
@property(nullable, copy) NSArray *colors;

/* An optional array of NSNumber objects defining the location of each
* gradient stop as a value in the range [0,1]. The values must be
* monotonically increasing. If a nil array is given, the stops are
* assumed to spread uniformly across the [0,1] range. When rendered,
* the colors are mapped to the output colorspace before being
* interpolated. Defaults to nil. Animatable. */

//数值为0-1，用于设置颜色渐变的区间分布
@property(nullable, copy) NSArray<NSNumber *> *locations;

/* The start and end points of the gradient when drawn into the layer's
* coordinate space. The start point corresponds to the first gradient
* stop, the end point to the last gradient stop. Both points are
* defined in a unit coordinate space that is then mapped to the
* layer's bounds rectangle when drawn. (I.e. [0,0] is the bottom-left
* corner of the layer, [1,1] is the top-right corner.) The default values
* are [.5,0] and [.5,1] respectively. Both are animatable. */

//对应locations中的第一个位置，默认值是(0.5,0.0)，下同
@property CGPoint startPoint;
@property CGPoint endPoint;

/* The kind of gradient that will be drawn. Currently the only allowed
* value is `axial' (the default value). */

//<span class="s1">就一个默认值是kCAGradientLayerAxial，表示按像素均匀变化</span>
@property(copy) NSString *type;

@end

/** `type' values. **/

CA_EXTERN NSString * const kCAGradientLayerAxial
__OSX_AVAILABLE_STARTING (__MAC_10_6, __IPHONE_3_0);

NS_ASSUME_NONNULL_END
2、代码实例：
在屏幕中间放一个view：



代码：

//
// ViewController.m
// 001-CAGradientLayer
//

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIView *myView;

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

CAGradientLayer * gradLayer = [CAGradientLayer layer];

gradLayer.frame = _myView.layer.bounds;

gradLayer.colors = [NSArray arrayWithObjects:
(id)[UIColor purpleColor].CGColor,
(id)[UIColor yellowColor].CGColor,
(id)[UIColor grayColor].CGColor,
(id)[UIColor orangeColor].CGColor,
(id)[UIColor blueColor].CGColor,
nil];

//颜色渐变的区间分布，如果不设置，会平均分布
gradLayer.locations = [NSArray arrayWithObjects:
[NSNumber numberWithFloat:0.0f],
[NSNumber numberWithFloat:0.2f],
[NSNumber numberWithFloat:0.5f],
[NSNumber numberWithFloat:0.8f],
[NSNumber numberWithFloat:1.0f],
nil];

// gradLayer.startPoint = CGPointMake(0, 0);
//
// gradLayer.endPoint = CGPointMake(1, 1);

[_myView.layer addSublayer:gradLayer];

}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end
首先注释掉startPoint和endPoint：



去掉注释：