当前UIScrollView滚动到顶

实现步骤:(前提是使用纯代码实现Navigation和tabBarController)

• 1. 创建类
• .h文件

#import 

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

• .m文件

#import "TopWindow.h"

@implementation TopWindow

static UIWindow *window_;
+ (void)show
{
    // UIWindowLevelAlert > UIWindowLevelStatusBar > UIWindowLevelNormal
    
    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;
        window_.backgroundColor = [UIColor clearColor];
        window_.windowLevel = UIWindowLevelAlert;
        window_.hidden = NO;
        [window_ addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(topWindowClick)]];
    });
}

+ (void)topWindowClick
{
    // 主窗口
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    
    // 查找主窗口中的所有scrollView
    [self findScrollViewsInView:window];
}

/**
 *  查找view中的所有scrollView
 */
+ (void)findScrollViewsInView:(UIView *)view
{
    // 利用递归查找所有的子控件
    for (UIView *subview in view.subviews) {
        [self findScrollViewsInView:subview];
    }
    
    // 如果不是scrollView
    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];
}
@end

• 2.在AppDelegate.m遵守协议
  UITabBarControllerDelegate
• 3.创建属性
  /** 记录上一次选中的子控制器的索引 */
  @property (nonatomic, assign) NSUInteger lastSelectedIndex;
• 4.实现方法

NSString * const WMTabBarButtonDidRepeatClickNotification = @"WMTabBarButtonDidRepeatClickNotification";
#pragma mark - 
- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    if (tabBarController.selectedIndex == self.lastSelectedIndex) { // 重复点击了同一个TabBar按钮
        // 发出通知
        [[NSNotificationCenter defaultCenter] postNotificationName:XMGTabBarButtonDidRepeatClickNotification object:nil];
    }
    // 记录目前选中的索引
    self.lastSelectedIndex = tabBarController.selectedIndex;
}

• 3.在AppDelegate.m调用方法

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    // 添加一个最高级别的顶层window
    [WMTopWindow show];
    
    return YES;
}