iOS CAGradientLayer 详解

参考文章 http://blog.youkuaiyun.com/iunion/article/details/26221213

CAGradientLayer

产生平滑过渡色

//
//  ViewController.m
//  test_gradient_01
//
//  Created by admin on 2/3/16.
//  Copyright © 2016 jeffasd. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@property(nonatomic, strong)UIView *contentView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    _contentView = [UIView new];
    _contentView.frame = CGRectMake(100, 100, 100, 100);
    _contentView.backgroundColor = [UIColor redColor];
    [self.view addSubview:_contentView];
    
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.contentView.bounds;
    [self.contentView.layer addSublayer:gradientLayer];
    
//    gradientLayer.colors = (__bridge NSArray * _Nullable)([UIColor blueColor].CGColor);
//    gradientLayer.colors = (__bridge NSArray * _Nullable)([UIColor cyanColor].CGColor);
    
    //渐变区域
    gradientLayer.locations = @[[NSNumber numberWithFloat:0.3], [NSNumber numberWithFloat:0.8]];
    
    gradientLayer.colors = @[(__bridge NSArray * _Nullable)([UIColor blueColor].CGColor), (__bridge NSArray * _Nullable)([UIColor redColor].CGColor)];
    
//    gradientLayer.startPoint = CGPointMake(0, 0);
    //最大值为 (1, 1),最小值为(0, 0)
    gradientLayer.startPoint = CGPointMake(1, 0);
    gradientLayer.endPoint = CGPointMake(1, 1);
    
}

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

@end

CAGradientLayer的属性设置

1. 类型

[objc]  view plain  copy

 print ?

1. @property(copy) NSString *type  

目前只有NSString * const kCAGradientLayerAxial
即线性梯度变化

2. 颜色

[objc]  view plain  copy

 print ?

1. @property(copy) NSArray *colors  

3. 位置参数

[objc]  view plain  copy

 print ?

1. @property(copy) NSArray *locations  

颜色的区间分布，locations的数组长度和colors一致， 取值范围(0, 1)，而且必须是单调递增的

修改例子6.6，增加

[objc]  view plain  copy

 print ?

1. <p class="p1">    gradientLayer.<span class="s1">locations</span> = <span class="s2">@[</span>[<span class="s1">NSNumber</span> <span class="s3">numberWithFloat</span>:<span class="s2">0.0</span>], [<span class="s1">NSNumber</span> <span class="s3">numberWithFloat</span>:<span class="s2">0.2</span>]<span class="s2">]</span>;</p>  

[objc]  view plain  copy

 print ?

1. gradientLayer.locations = @[[NSNumber numberWithFloat:0.5], [NSNumber numberWithFloat:0.7]];  

4. startPoint和endPoint

[objc]  view plain  copy

 print ?

1. @property CGPoint startPoint, endPoint;  

取值都是相对于layer的bounds的。startPoint默认值为(0.5, 0)，endPoint默认值为(0.5, 1)

修改例子6.6

gradientLayer.startPoint 分别设为 CGPointMake(0, 0); 

  CGPointMake( 0.25,  0); 

  CGPointMake( 0.5,  0); 

  CGPointMake( 0.75,  0); 

  CGPointMake(1,  0); 

综合修改例子6.6

[objc]  view plain  copy

 print ?

1. - (void)viewDidLoad  
2. {  
3.     [super viewDidLoad];  
4.       
5.     //create gradient layer and add it to our container view  
6.     CAGradientLayer *gradientLayer = [CAGradientLayer layer];  
7.     gradientLayer.frame = self.containerView.bounds;  
8.     [self.containerView.layer addSublayer:gradientLayer];  
9.       
10.     //set gradient colors  
11.     gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor,  
12.                              (__bridge id)[UIColor blueColor].CGColor];  
13.       
14.     gradientLayer.locations = @[[NSNumber numberWithFloat:0.5], [NSNumber numberWithFloat:0.7]];  
15.   
16.     //set gradient start and end points  
17.     gradientLayer.startPoint = CGPointMake(0.75, 0.0);  
18.     gradientLayer.endPoint = CGPointMake(1.0, 1.0);  
19. }  

从以上可以看出startPoint和endPoint诗表示的渐变方向，locations是渐变区域。

也可以看出locations的取值是相对于startPoint和endPoint线段的。

在网上找的描述让我很是不能理解