还是直接上代码，有什么问题的话，直接评论。
1.在YYTScratchView.h文件中
//
// YYTScratchView.h
// Demo-刮奖
//
// Created by yyt on 16/4/20.
// Copyright © 2016年 yyt. All rights reserved.
//
#import <UIKit/UIKit.h>
@interface YYTScratchView : UIView
@property (nonatomic,assign) float sizeBrush;
-(void)setHideView:(UIView*) hideView;
@end
2在YYTScratchView.m文件中
//
// YYTScratchView.m
// Demo-刮奖
//
// Created by yyt on 16/4/20.
// Copyright © 2016年 yyt. All rights reserved.
//
#import "YYTScratchView.h"
@interface YYTScratchView (){
CGContextRef _contextMask;//maskContext 用户touch 改变的context
CGImageRef _scratchCGImg;//CGimageRef 封装_contextMask 图片信息 _contextMask改变 跟着改变 直到 调用生成UIImage
CGPoint currPonit;
CGPoint prePoint;
}
@end
@implementation YYTScratchView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self setOpaque:NO];
//设置透明 如果不透明就没法看到下一层了
self.sizeBrush=10.0f;
}
return self;
}
- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];
UIImage* imageToDraw=[UIImage imageWithCGImage:_scratchCGImg];
[imageToDraw drawInRect:self.frame];
}
//setSizeBrush before setHideView
-(void)setHideView:(UIView*) hideView{
CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceGray();
CGFloat scale = [UIScreen mainScreen].scale;
//获得当前传入View的CGImage
UIGraphicsBeginImageContextWithOptions(hideView.bounds.size, NO, 0);
hideView.layer.contentsScale=scale;
[hideView.layer renderInContext:UIGraphicsGetCurrentContext()];
CGImageRef hideCGImg=UIGraphicsGetImageFromCurrentImageContext().CGImage;
UIGraphicsEndImageContext();
//绘制Bitmap掩码
size_t width=CGImageGetWidth(hideCGImg);
size_t height=CGImageGetHeight(hideCGImg);
CFMutableDataRef pixels;
pixels=CFDataCreateMutable(NULL, width*height);
//创建一个可变的dataRef 用于bitmap存储记录
_contextMask = CGBitmapContextCreate(CFDataGetMutableBytePtr(pixels), width, height , 8, width, colorSpace, kCGImageAlphaNone);
//数据提供者
CGDataProviderRef dataProvider=CGDataProviderCreateWithCFData(pixels);
//填充黑色背景 mask中黑色范围为显示内容 白色为不显示
CGContextSetFillColorWithColor(_contextMask, [UIColor blackColor].CGColor);
CGContextFillRect(_contextMask, self.frame);
CGContextSetStrokeColorWithColor(_contextMask, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(_contextMask, self.sizeBrush);
CGContextSetLineCap(_contextMask, kCGLineCapRound);
CGImageRef mask=CGImageMaskCreate(width, height, 8, 8, width, dataProvider, nil, NO);
_scratchCGImg=CGImageCreateWithMask(hideCGImg, mask);
CGImageRelease(mask);
CGColorSpaceRelease(colorSpace);
}
-(void)scratchViewFrom:(CGPoint)startPoint toEnd:(CGPoint)endPoint{
float scale=[UIScreen mainScreen].scale;
//CG的Y与UI的是反的 UI的y0在左上角 CG在左下
CGContextMoveToPoint(_contextMask, startPoint.x*scale, (self.frame.size.height-startPoint.y)*scale);
CGContextAddLineToPoint(_contextMask, endPoint.x*scale,(self.frame.size.height-endPoint.y)*scale);
CGContextStrokePath(_contextMask);
[self setNeedsDisplay];
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
[super touchesBegan:touches withEvent:event];
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
[super touchesMoved:touches withEvent:event];
UITouch *touch=[touches anyObject];
currPonit=[touch locationInView:self];
prePoint=[touch previousLocationInView:self];
[self scratchViewFrom:prePoint toEnd:currPonit];
}
-(void)toucheseEnd:(NSSet *)touches withEvent:(UIEvent *)event{
[super touchesEnded:touches withEvent:event];
UITouch *touch=[touches anyObject];
currPonit=[touch locationInView:self];
prePoint=[touch previousLocationInView:self];
[self scratchViewFrom:prePoint toEnd:currPonit];
}
-(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event{
[super touchesCancelled:touches withEvent:event];
}
@end
3.在需要调用的地方
//
// ViewController.m
// Demo-刮奖
//
// Created by yyt on 16/4/20.
// Copyright © 2016年 yyt. All rights reserved.
//
#import "ViewController.h"
#import "YYTScratchView.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
imageView.image = [UIImage imageNamed:@"11.png"];
[self.view addSubview:imageView];
UIImageView *imageView2 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
imageView2.image = [UIImage imageNamed:@"22.png"];
//[self.view addSubview:imageView];
YYTScratchView *scratchView = [[YYTScratchView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
scratchView.sizeBrush = 20.0;
[scratchView setHideView:imageView2];
[self.view addSubview:scratchView];
}
@end