一、前言
在我们IOS开发中，UIScrollView自带有点击顶部状态栏自动返回顶部的效果，不过这个效果是有约束条件的：
// When the user taps the status bar, the scroll view beneath the touch which is closest to the status bar will be scrolled to top, but only if its `scrollsToTop` property is YES, its delegate does not return NO from `shouldScrollViewScrollToTop`, and it is not already at the top.// On iPhone, we execute this gesture only if there's one on-screen scroll view with `scrollsToTop` == YES. If more than one is found, none will be scrolled.@property(nonatomic) BOOL scrollsToTop __TVOS_PROHIBITED; // default is YES.
即这个手势只能作用在一个scrollView上，当发现多个时，手势将会失效。
在实际应用中，我们可能会有多个scrollView（包含UITableView/UICollectionView），如汽车之家、网易新闻、爱奇艺等等应用，这时候，系统默认的点击状态栏返回到顶部效果就会失效，我们就得自己自定义控件来实现此功能了。二、主要技术点
抛开常用的技术点，主要用到的技术点有：
- 多窗口应用
- 递归
- 坐标系转换
- 触摸事件响应（横竖屏切换时需要）
PS：由于最近刚回武汉忙着找工作，所以没有花太多时间在简书上面，我先把代码放上来，后续再重新整理
#import "TopWindow.h"@implementation TopWindowstatic UIWindow *topWindow_;/** * 显示顶部窗口 */+ (void)show{ dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ topWindow_ = [[UIWindow alloc] init]; topWindow_.windowLevel = UIWindowLevelAlert; topWindow_.frame = [UIApplication sharedApplication].statusBarFrame; topWindow_.backgroundColor = [UIColor clearColor]; topWindow_.hidden = NO; [topWindow_ addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(topWindowClick)]]; });}/** * 监听顶部窗口点击 */+ (void)topWindowClick{ UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow; [self searchAllScrollViewsInView:keyWindow];}/** * 找到参数view中所有的UIScrollView */+ (void)searchAllScrollViewsInView:(UIView *)view{ // 递归遍历所有的子控件 for (UIView *subview in view.subviews) { [self searchAllScrollViewsInView:subview]; } // 判断子控件类型(如果不是UIScrollView，直接返回) if (![view isKindOfClass:[UIScrollView class]]) return; // 找到了UIScrollView UIScrollView *scrollView = (UIScrollView *)view; // 判断UIScrollView是否和window重叠（如果UIScrollView跟window没有重叠，直接返回） if (![scrollView bs_intersectsWithAnotherView:nil]) return; // 让UIScrollView滚动到最前面 // 让CGRectMake(0, 0, 1, 1)这个矩形框完全显示在scrollView的frame框中 [scrollView scrollRectToVisible:CGRectMake(0, 0, 1, 1) animated:YES];}@end