前言

在开发中，遇到了计算View显示的百分比来表明是否曝光
主要的场景就是在滑动列表中View展示的百分比。

RXViewVisiableCell

@implementation RXViewVisiableCell
- (void)refreshViewWithIndex:(NSInteger)index {
    if (self.label == nil) {
        // cell height = 200
        self.label = [[UILabel alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 100)];
        self.label.textColor = [UIColor whiteColor];
        self.label.backgroundColor = [UIColor redColor];
        [self.contentView addSubview:self.label];
    }
    NSLog(@"refreshViewWithIndex self.hidden:%zd", (long)self.hidden);
    self.label.text = [NSString stringWithFormat:@"%zd", (long)index];
    if (index == 4) {
        [self startTimer];
    } else {
        [self endTimer];
    }
}
- (void)startTimer {
    if (self.timer == nil) {
        __weak typeof(self) weakSelf = self;
        self.timer = [NSTimer rxv_scheduleTimerWithTimeInterval:1.0 repeats:YES usingBlock:^(NSTimer * _Nonnull timer) {
            CGFloat percent = [weakSelf.label rxv_viewVisiable];
            NSLog(@"visiableCell index:%@ percent:%.3f self:%p self.label:%p self.hidden:%zd", weakSelf.label.text, percent, weakSelf, weakSelf.label, (long)weakSelf.hidden);
            if (weakSelf.hidden) {
                NSLog(@"timer find cell hidden, need to endTimer");
                [weakSelf endTimer];
            }
        }];
    }
}

- (void)endTimer {
    [self.timer invalidate];
    self.timer = nil;
}
@end

UIView+RXVerify.h

- (CGFloat)rxv_viewVisiable {
    // 未添加到superview
    if (self.superview == nil) {
        return 0;
    }
    // view 隐藏
    if (self.hidden) {
        return 0;
    }
    UIView *rootView = self;
    while (rootView != nil) {
        UIView *superView = rootView.superview;
        if (superView.hidden) {
            return 0;
        }
        if (superView == nil) {
            break;
        }
        rootView = superView;
    }
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    UIScrollView *scrollView = nil;
    UIView *pView = self;
    while (pView != nil) {
        if ([pView isKindOfClass:[UIScrollView class]]) {
            scrollView = (UIScrollView *)pView;
            break;
        }
        pView = pView.superview;
    }
    UIView *visiableView = scrollView ? scrollView : window;
    CGRect rect = [visiableView convertRect:self.frame fromView:self.superview];
    if (CGRectIsEmpty(rect) || CGRectIsNull(rect) || CGSizeEqualToSize(rect.size, CGSizeZero)) {
        return 0;
    }
    // 获取 该view与visiableView 交叉的 Rect
    CGRect screenRect = visiableView.bounds;
    CGRect intersectionRect = CGRectIntersection(rect, screenRect);
    if (CGRectIsEmpty(intersectionRect) || CGRectIsNull(intersectionRect)) {
        return 0;
    }
    // 展示面积与实际面积的百分比
    CGFloat dividend = intersectionRect.size.width * intersectionRect.size.height;
    CGFloat divisor = (self.frame.size.width * self.frame.size.height);
    CGFloat showPercent = dividend / divisor;
    return showPercent;
}
@end

重点

1. superView.hidden 如果其中之一的superview hidden了，那么就是0
2. UIView *visiableView = scrollView ? scrollView : window; 如果在其中之一的superview找到scrollView，那么以这个scrollView为基础进行判断 (这里有一个潜在的假设是此scrollView处在屏幕中)