点击状态栏回到顶部两种实现

1.局部设置

scrollView有个属性scrollsToTop，默认值为YES. 所以默认情况下点击状态栏就可以回到顶部。但当一个控制器中有多个scrollView或其子类时，因为默认值都是YES,所以系统不知道要让哪个scrollView回到顶部。所以要让需要回到顶部的scrollView.scrollsToTop = YES,而其他的scrollView的设置成NO.

2.全局设置

新建一个window,windowLevel为alert的，背景色为clear,加一个手势，设置点击事件。

注意，iOS9之后，每个window都要设置一个rootViewController

一个范例：

@implementation TopWindow

static UIWindow *window_;

+ (void)initialize
{
    window_ = [[UIWindow alloc] init];
    window_.backgroundColor = [UIColor clearColor];
    window_.frame = CGRectMake(0, 0, XMGScreenW, 20);
    window_.windowLevel = UIWindowLevelAlert;
    [window_ addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(windowClick)]];
    UIViewController *vc = [[UIViewController alloc]init];
    
    vc.view.backgroundColor = [UIColor clearColor];
    window_.rootViewController = vc;
}

+ (void)show
{
    window_.hidden = NO;
}

+ (void)hide
{
    window_.hidden = YES;
}

/**
 * 监听窗口点击
 */
+ (void)windowClick
{
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    [self searchScrollViewInView:window];
}

+ (void)searchScrollViewInView:(UIView *)superview
{
    for (UIScrollView *subview in superview.subviews) {
        // 如果是scrollview, 滚动最顶部
        if ([subview isKindOfClass:[UIScrollView class]] && subview.isShowingOnKeyWindow) {
            CGPoint offset = subview.contentOffset;
            offset.y = - subview.contentInset.top;
            [subview setContentOffset:offset animated:YES];
        }
        
        // 继续查找子控件
        [self searchScrollViewInView:subview];
    }
}
@end


//UIView的一个分类方法

- (BOOL)isShowingOnKeyWindow

{

    // 主窗口

    UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;

// 以主窗口左上角为坐标原点, 计算self的矩形框

CGRect newFrame = [keyWindow convertRect:self.frame fromView:self.superview];

 CGRect winBounds = keyWindow.bounds;

  // 主窗口的bounds 和 self的矩形框 是否有重叠

    BOOL intersects = CGRectIntersectsRect(newFrame, winBounds);

 return !self.isHidden && self.alpha > 0.01 && self.window == keyWindow && intersects;

}