iOS引导视图镂空效果

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- (void)showViewRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius
{
    [[UIApplication sharedApplication].keyWindow addSubview:self];
    CGRect frame = [UIScreen mainScreen].bounds;
    [self addSubview:self.imageView];

    // 第一个路径
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:frame];
    // 透明path
    UIBezierPath *path2 = [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius] bezierPathByReversingPath];

    [path appendPath:path2];
    // 绘制透明区域
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = path.CGPath;
    [self.layer setMask:shapeLayer];

    self.imageView.centerX = CGRectGetCenter(rect).x - self.imageView.width * 0.5;
    self.imageView.y = CGRectGetMaxY(rect) + 20;
}