使用maskView设计动画效果

    //MARK:1. maskView（maskLayer）基本原理
    
    CGFloat width = 120.f;
    
    //底图
    self.baseImageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20, width, width)];
    [_baseImageView setImage:[UIImage imageNamed:@"base"]];
    [self.view addSubview:_baseImageView];
    
    //mask 是有透明的
    self.maskImageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20 + width + 20, width, width)];
    [_maskImageView setImage:[UIImage imageNamed:@"mask"]];
    [self.view addSubview:_maskImageView];
    
    //使用maskView的情况
    self.addImageView  = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20 + (width + 20) * 2, width, width)];
    [_addImageView setImage:[UIImage imageNamed:@"base"]];
    UIImageView *mask  = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, width, width)];
    [mask setImage:[UIImage imageNamed:@"mask"]];
    
    [_addImageView setMaskView:mask];//iOS8.0之后才有 maskView不能用addSubView的方式来添加遮罩!!!
    
    /*iOS 8之前
//    CALayer *layer = [CALayer layer];
//    [layer setFrame:CGRectMake(0, 0, width, width)];
//    [layer setContents:(id)[UIImage imageNamed:@"mask"].CGImage];
//    [_addImageView.layer setMask:layer];
    */
     
    [self.view addSubview:_addImageView];
    
    
    
    
    //MARK:2. maskView配合CAGradientLayer的使用
    
    // 第一步 加载图片
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(width + 40, 20, 200, 200)];
    [imageView setImage:[UIImage imageNamed:@"base"]];
    [self.view addSubview:imageView];
    // 第二步 创建出CAGradientLayer
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    [gradientLayer setFrame:imageView.bounds];//遮罩层的区域
    [gradientLayer setColors:@[(__bridge id)[UIColor clearColor].CGColor,
                               (__bridge id)[UIColor blackColor].CGColor,
                               (__bridge id)[UIColor clearColor].CGColor]];//渐变的颜色数组 __bridge id类型
    [gradientLayer setLocations:@[@(0.25),@(0.5),@(0.75)]];//渐变的区域 整个是1 0.25就是1/4处以此类推
    [gradientLayer setStartPoint:CGPointMake(0, 0)];
    [gradientLayer setEndPoint:CGPointMake(1, 0)];//渐变的方向(1,0)就是横向 (1,1)就是从左上角到右下角以此类推
    // 第三步 创建一个容器View 用于加载创建出的CAGradientLayer
    UIView *containerView = [[UIView alloc]initWithFrame:imageView.bounds];
    [containerView.layer addSublayer:gradientLayer];
    // 最后 设定maskView
    imageView.maskView = containerView;
    
    // 扩展 给maskView做动画 除了修改容器view的fram值之外 还可以动态的修改location startPoint endPoint等 实现很绚丽的动画效果
    CGRect frame        = containerView.frame;
    frame.origin.x     -= 200;//这里200是图片的宽 也就是让容器View的最右边和底层图片的最左边重合
    containerView.frame = frame;
    [UIView animateWithDuration:4.0f animations:^{
        CGRect frame    = containerView.frame;//改变位移
        frame.origin.x += 400;//从左移动到右边
        containerView.frame = frame;//重新赋值
    }];
    
    
    
    
    //MARK:3. maskView配合alpha通道图片的使用
    // 添加背景图
    UIImageView *backgroundView = [[UIImageView alloc]initWithFrame:CGRectMake(width + 40, 200 + 40, 200, 200)];
    [backgroundView setImage:[UIImage imageNamed:@"background"]];
    [self.view addSubview:backgroundView];
    
    
    // 待切换图
    UIImageView *baseView = [[UIImageView alloc]initWithFrame:backgroundView.frame];
    [baseView setImage:[UIImage imageNamed:@"base"]];
    [self.view addSubview:baseView];
    
    
    // 创建maskView作为容器
    UIView *maskView  = [[UIView alloc]initWithFrame:baseView.bounds];
    baseView.maskView = maskView;
    
    
    //maskView的subView1
    UIImageView *picOne = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 100, 400)];//100背景宽一半,400背景高两倍 1的上半部是alpha为0
    [picOne setImage:[UIImage imageNamed:@"1"]];
    [maskView addSubview:picOne];
    
    //maskView的subView2
    UIImageView *picTwo = [[UIImageView alloc]initWithFrame:CGRectMake(100, -200, 100, 400)];//2的下半部alpha为0
    [picTwo setImage:[UIImage imageNamed:@"2"]];
    [maskView addSubview:picTwo];
    
    
    //做切换图片的动画
    [UIView animateWithDuration:2.0f animations:^{
        CGRect oneFrame    = picOne.frame;
        oneFrame.origin.y -= 400;
        picOne.frame       = oneFrame;
        
        CGRect twoFrame    = picTwo.frame;
        twoFrame.origin.y += 400;
        picTwo.frame       = twoFrame;
    }];
    
    
    
    
    //MARK:4. 设计文本横向渐变消失的控件
    [self.view setBackgroundColor:[UIColor grayColor]];
    
    // 创建FadeString
    FadeString *fadeString = [[FadeString alloc]initWithFrame:CGRectMake(0, 400+40, 300, 40)];
    [fadeString setCenter:CGPointMake(self.view.center.x, fadeString.center.y)];
    fadeString.text = @"这个效果看起来还是不错的";
    [self.view addSubview:fadeString];
    
    
    // 执行动画效果
    [fadeString fadeRight];

// 输入的文本
@property (nonatomic, strong) NSString *text;

// 向右渐变消失的方法
- (void)fadeRight;

#import "FadeString.h"

@interface FadeString ()

@property (nonatomic, strong) UILabel *label; // 显示文字的label
@property (nonatomic, strong) UIView  *mask;  // 作为遮罩的mask

@end


@implementation FadeString
- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        // 创建出label
        [self createLabel:self.bounds];
        // 创建出mask
        [self createMask:self.bounds];
    }
    return self;
}

- (void)createLabel:(CGRect)frame {
    self.label = [[UILabel alloc]initWithFrame:frame];
    [_label setFont:[UIFont systemFontOfSize:25.0f]];
    [_label setTextAlignment:NSTextAlignmentCenter];
    [_label setTextColor:[UIColor whiteColor]];
    
    [self addSubview:_label];
}
- (void)createMask:(CGRect)frame {
    //创建出渐变的layer
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    [gradientLayer setFrame:frame];
    [gradientLayer setColors:@[(__bridge id)[UIColor clearColor].CGColor,
                               (__bridge id)[UIColor blackColor].CGColor,
                               (__bridge id)[UIColor blackColor].CGColor,
                               (__bridge id)[UIColor clearColor].CGColor]];
    [gradientLayer setLocations:@[@(0.01), @(0.1), @(0.9), @(0.99)]];
    [gradientLayer setStartPoint:CGPointMake(0, 0)];
    [gradientLayer setEndPoint:CGPointMake(1, 0)];
    
    // 创建并接管mask
    self.mask     = [[UIView alloc]initWithFrame:frame];
    // mask获取渐变layer
    [self.mask.layer addSublayer:gradientLayer];
    self.maskView = _mask;
}


- (void)fadeRight {
    //当前的设计是有缺陷的 最好加上两个参数 一个动画时间 一个是否执行动画
    
    [UIView animateWithDuration:3.f animations:^{
        CGRect maskFrame    = _mask.frame;
        maskFrame.origin.x += _mask.frame.size.width;
        _mask.frame         = maskFrame;
    }];
}

//MARK:重写set,get方法
@synthesize text = _text;
- (void)setText:(NSString *)text {
    _text           = text;
    self.label.text = text;
}
- (NSString *)text {
    return _text;
}
/*
 // Only override drawRect: if you perform custom drawing.
 // An empty implementation adversely affects performance during animation.
 - (void)drawRect:(CGRect)rect {
 // Drawing code
 }
 */

@end