iOS 导航栏隐藏现实正确方式

- (void)viewWillAppear:(BOOL)animated {
    [self.navigationController setNavigationBarHidden:NO animated:animated];
    [super viewWillAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated {
    [self.navigationController setNavigationBarHidden:YES animated:animated];
    [super viewWillDisappear:animated];
}

还有两个关键属性pus进去pop回来20像素高度问题。使用这两个属性。

    if( ([[[UIDevice currentDevice] systemVersion] doubleValue]>=7.0)) {
        self.edgesForExtendedLayout=UIRectEdgeNone;
        self.navigationController.navigationBar.translucent = NO;
    }
或者直接
  self.edgesForExtendedLayout=UIRectEdgeNone;
  self.navigationController.navigationBar.translucent = NO;
这里还有个坑。已经解决。
iOS11的系统edgesForExtendedLayout方法弃用。使用下面的可以完美解决。亲测iOS10和11的系统都没多那20像素。
    if (@available(iOS 11.0, *)) {
        
        UIScrollView.appearance.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
        
    } else {
      self.automaticallyAdjustsScrollViewInsets = NO;
        //self.edgesForExtendedLayout = UIRectEdgeNone;
        // Fallback on earlier versions
    }