橡皮擦

- (void)viewDidLoad {

    [super viewDidLoad];

    //初始化要显示在下面的提示label

    UILabel*label = [[UILabelalloc]initWithFrame:CGRectMake(100,100,200,50)];

    label.textAlignment = NSTextAlignmentCenter;

    label.text=@"刮开看看你中奖啦!";

    [self.viewaddSubview:label];

    //初始化显示在上面的imageview(用上面的根据颜色生成图片方法生成一个灰色的图层,看起来像一种刮奖的图层)

    self.imageView= [[UIImageViewalloc]init];

    self.imageView.image= [selfimageWithColor:[UIColorgrayColor]];

    self.imageView.frame=CGRectMake(100,100,200,50);

    [self.viewaddSubview:self.imageView];

}

//刮奖()

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent*)event

{

    UITouch*touch = touches.anyObject;

    CGPointpoint = [touchlocationInView:self.imageView];

    //滑块区域(触碰到的点放大成正方形)

    CGRectrect =  CGRectMake( point.x-10,point.y-10,20,20);

    //获取上下文(这里记得一定要透明)

    UIGraphicsBeginImageContextWithOptions(self.imageView.bounds.size, NO, 0);

    CGContextRefref =  UIGraphicsGetCurrentContext();

    //把imageView的layer映射到上下文中(这个是核心,由于UIView本质上显示东西的layer层,所以实质是将imageView显示的东西全部复制给上下文,app中长用到的截屏就利用了这个原理)

    [self.imageView.layer renderInContext:ref];

    //清除划过的区域

    CGContextClearRect(ref, rect);

    UIImage *image =UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    //返回图片并不断的传给UIImageView上去显示

    self.imageView.image= image;

}

- (UIImage*)imageWithColor:(UIColor*)color {

    CGRectrect =CGRectMake(0.0f,0.0f,1.0f,1.0f);

    UIGraphicsBeginImageContext(rect.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [color CGColor]);

    CGContextFillRect(context, rect);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    returnimage;

}