CAGradientLayer處理顔色漸變效果

1、這個類很簡單，下面簡單介紹

/* 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. */

//這個數組裡面儲存了用于漸變的顔色
@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. */

//數值為0-1，用于設定顔色漸變的區間分布
@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. */

//對應locations中的第一個位置，預設值是(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">就一個預設值是kCAGradientLayerAxial，表示按像素均勻變化</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、代碼執行個體：

在螢幕中間放一個view：

代碼：

//
//  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];
    
    //顔色漸變的區間分布，如果不設定，會平均分布
    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
           

首先注釋掉startPoint和endPoint：

去掉注釋：