CAGradientLayer实现图片渐变透明效果

CAGradientLayer实现图片渐变透明效果

要实现的效果如下:

源码:

//

//  RootViewController.m

//  CAGradientLayer

//

//  Copyright (c) 2014年 Y.X. All rights reserved.

//

#import "RootViewController.h"

#import "YXGCD.h"
@interface RootViewController ()
@property (nonatomic, strong) GCDTimer   *timer;
@end
@implementation RootViewController
- (void)viewDidLoad

{

    [super viewDidLoad];
self.view.backgroundColor = [UIColor redColor];
// 背景图片

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];

    imageView.image = [UIImage imageNamed:@"猫"];

    [self.view addSubview:imageView];
UIView *yourGradientView = [[UIView alloc] initWithFrame:self.view.bounds];
// 渐变图层

    CAGradientLayer *gradientLayer = [CAGradientLayer layer];

    gradientLayer.frame = yourGradientView.bounds;
// 设置颜色

    gradientLayer.colors = @[(id)[[UIColor clearColor] colorWithAlphaComponent:0.0f].CGColor,

                             (id)[[UIColor redColor] colorWithAlphaComponent:1.0f].CGColor];

    gradientLayer.locations = @[[NSNumber numberWithFloat:0.7f],

                                [NSNumber numberWithFloat:1.0f]];
// 添加渐变图层

    [yourGradientView.layer addSublayer:gradientLayer];

    [self.view addSubview:yourGradientView];
// 开始动画效果

    _timer = [[GCDTimer alloc] initInQueue:[GCDQueue mainQueue]];

    [_timer event:^{

        gradientLayer.locations = @[[NSNumber numberWithFloat:arc4random()%100/100.f],

                                    [NSNumber numberWithFloat:1.0f]];
gradientLayer.colors = @[(id)[[UIColor clearColor] colorWithAlphaComponent:0.0f].CGColor,

                                 (id)[[UIColor colorWithRed:arc4random()%255/255.f

                                                      green:arc4random()%255/255.f

                                                       blue:arc4random()%255/255.f

                                                      alpha:1.0] colorWithAlphaComponent:1.0f].CGColor];

    } timeInterval:NSEC_PER_SEC];

    [_timer start];

}
@end

效果如下:

核心的地方:

colors与locations一一对应,而且,颜色的值是可以设置透明度的,这点相当重要哦.

附录:

http://stackoverflow.com/questions/22755016/how-to-achieve-this-effect-in-iphone-sdk/22755078#22755078

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