需求:点击顶部statusBar,scrollView滚动到最顶部

当控制器上面只有一个UIScrollView的时候,系统才会为这个UIScrollView添加这个自动回滚到顶部的功能

当一个控制器上有多个UIScrollView时,系统就懵了,因为他不确定到底要为那个UIScrollView设置这个自动回滚到顶部的功能,这个时候就只能有我们coder明确的告诉系统:我们要为哪个UIScrollView设置自动回滚到顶部的功能

我们只为显示在用户眼前的UIScrollView设置那个功能

#import <Foundation/Foundation.h>

@interface DXTopWindow : NSObject
+ (void)show;
@end

// 声明一个全局变量
static UIWindow *window_;
+ (void)show{
    // 延迟加载窗口,保证这个窗口在所有窗口的最上面
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        window_ = [[UIWindow alloc] init];
        window_.frame = [UIApplication sharedApplication].statusBarFrame;
        //修正frame,避免遮挡
        window_.frame=CGRectMake(100+window_.frame.origin.x, window_.frame.origin.y, window_.frame.size.width, window_.frame.size.height);
        // 窗口默认显示黑色
        window_.backgroundColor = [UIColor clearColor];//点击事件可以获取？？
        // UIWindowLevelAlert > UIWindowLevelStatusBar > UIWindowLevelNormal
        // 窗口默认等级是UIWindowLevelNormal,等级最低,放在最下层,点击手势被拦截,无法被监听到
        window_.windowLevel = UIWindowLevelAlert;
        // 默认是隐藏的
        window_.hidden = NO;
        [window_ addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(topWindowClick)]];
       // [window_ makeKeyAndVisible];
        
    });
}
+ (void)topWindowClick{
    // 主窗口
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    // 查找主窗口中的所有scrollView
    [self findScrollViewsInView:window];
}

+ (void)findScrollViewsInView:(UIView *)view{
    // 窗口也继承UIView
    // 利用递归查找所有的子控件
    for (UIView *subview in view.subviews) {
        [self findScrollViewsInView:subview];
    }
    
    if (![view isKindOfClass:[UIScrollView class]]) return;
    // 判断是否跟window有重叠
    if (![view intersectWithView:[UIApplication sharedApplication].keyWindow]) return;
    //    CGRect windowRect = [UIApplication sharedApplication].keyWindow.bounds;
    //    CGRect viewRect = [view convertRect:view.bounds toView:nil];
    //    // 跟window不重叠
    //    if (!CGRectIntersectsRect(windowRect, viewRect)) return;
    // 如果是scrollView
    UIScrollView *scrollView = (UIScrollView *)view;
    // 修改offset
    CGPoint offset = scrollView.contentOffset;
    offset.y = - scrollView.contentInset.top;
    [scrollView setContentOffset:offset animated:YES];
    // [scrollView scrollRectToVisible:CGRectMake(0, 0, 1, 1) animated:YES];
}

给UIView扩展的分类方法

// 判断两个View是否相交
- (BOOL)intersectWithView:(UIView *)view{
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    CGRect selfRect = [self convertRect:self.bounds toView:window];
    CGRect viewRect = [view convertRect:view.bounds toView:window];
    
    return CGRectIntersectsRect(selfRect, viewRect);
}

使用了递归输出所有子控件应用示例

extension UIView {
    // 使用了递归输出所有子控件
    public class func dx_foundView(view: UIView, className: String) -> UIView? {

        if let tmpClass = NSClassFromString(className) {
            // 递归出口
            if view.isKind(of: tmpClass) {
                return view
            }
            
            for subView in view.subviews {
                let foundView = dx_foundView(view: subView, className: className)
                if foundView != nil {
                    return foundView
                }
            }
        }
        
        return nil
    }
}