iOS开发——项目需求-快速回到当前界面的顶部

@interface AppDelegate ()
@property (nonatomic, strong) UIWindow *topWindow;
@end

@implementation AppDelegate

- (UIWindow *)topWindow{
    
    if (_topWindow == nil) {
        
        _topWindow = [[UIWindow alloc] init];
        
        _topWindow.windowLevel = UIWindowLevelAlert;
        _topWindow.frame = CGRectMake(0, 0, CHGScreenW, 20);
        _topWindow.backgroundColor = [UIColor clearColor];
        // 这句很重要，默认是隐藏的，要想显示必须手动设置为NO
        _topWindow.hidden = NO;
        [_topWindow addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(topWindowClick)]];
    }
    return _topWindow;
}

- (void)topWindowClick
{
    NSArray *windows = [UIApplication sharedApplication].windows;
    for (UIWindow *window in windows) {
　　　　　　// 遍历该窗口下所有子控件
        [self searchSubviews:window];
    }
}

/**
 * 搜索superview内部的所有子控件
 */
- (void)searchSubviews:(UIView *)superview
{
    for (UIScrollView *scrollView in superview.subviews) {
        [self searchSubviews:scrollView];
        
        // 判断是否为 scrollView
        if (![scrollView isKindOfClass:[UIScrollView class]]) continue;
        
        // 判断scrollView是否在窗口上 （是否相交）
        // 计算出scrollView在window坐标系上的矩形框
        CGRect scrollViewRect = [scrollView convertRect:scrollView.bounds toView:scrollView.window];
        CGRect windowRect = scrollView.window.bounds;
        // 判断scrollView的边框是否和window的边框交叉
        if (!CGRectIntersectsRect(scrollViewRect, windowRect)) continue;
        
        // 能来到这里说明scrollView在窗口上,修改偏移量，滚到最顶部
        CGPoint offset = scrollView.contentOffset;
        offset.y =  - scrollView.contentInset.top;
        [scrollView setContentOffset:offset animated:YES];
    }
}

// 程序激活的时候调用topWindow
- (void)applicationDidBecomeActive:(UIApplication *)application {
    [self topWindow];
}