一个简单的遮挡效果

遮挡效果图：

效果图一
效果图二

原理：放两张视图，一张视图控制灰色星星，另一张控制黄色星星。
黄色星星覆盖灰色星星，再通过值来改变黄色星星的视图frame的宽度。

代码：

#import <UIKit/UIKit.h>
@interface starView : UIView {
    
    UIView *_yellowView;
    UIView *_grayView;    
}
@property(nonatomic,assign) float rating;
@end

#import "starView.h"

@implementation starView

//1.创建视图

- (void)awakeFromNib {
    
    UIImage *yellowImage = [UIImage imageNamed:@"yellow"];
    UIImage *grayImage = [UIImage imageNamed:@"gray"];
    
    _yellowView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, yellowImage.size.width* 5,yellowImage.size.height)];
    _grayView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, grayImage.size.width * 5, grayImage.size.height)];
    
    //通过图片来创建背景
    _yellowView.backgroundColor = [UIColor colorWithPatternImage:yellowImage];
    _grayView.backgroundColor = [UIColor colorWithPatternImage:grayImage];
    
    [self addSubview:_grayView];
    [self addSubview:_yellowView];
    
    //方法比例
    CGFloat scale = self.frame.size.height / yellowImage.size.height;
    _yellowView.transform = CGAffineTransformMakeScale(scale, scale);
    _grayView.transform = CGAffineTransformMakeScale(scale, scale);
    //坐标归零
    CGRect frame = self.frame;
    frame.origin = CGPointZero;
    _yellowView.frame = frame;
    _grayView.frame = frame;
    
    
}

//2.修改值
- (void)setRating:(float)rating {
    
    _rating = rating;
    
    float s = rating / 10;
    
    CGRect frame = _yellowView.frame;
    
    frame.size.width = self.frame.size.width * s;
    
    _yellowView.frame =frame;
    
}

@end