像 Instagram iOS 应用一样自动隐藏和显示 UINavigationBar

Question

我有这段代码：

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    UINavigationBar *navbar =self.navigationController.navigationBar;
    UIView *tableView = self.view;
    CGRect navBarFrame = self.navigationController.navigationBar.frame;

    CGRect tableFrame = self.view.frame;

    //changing the origin.y based on the current scroll view.
    //Adding +20 for the Status Bar since the offset is tied into that.

    navBarFrame.origin.y = MIN(0, MAX(-44, (scrollView.contentOffset.y * -1)))  +20 ;
    tableFrame.origin.y = navBarFrame.origin.y + navBarFrame.size.height;

    navbar.frame = navBarFrame;
    tableView.frame = tableFrame;

}

这给出了隐藏我的导航栏的预期效果，但只有当您滚动到滚动视图的顶部（y 偏移 = 0）时，导航才会重新出现。如何重新创建 Instagram 的行为，即每当您向上滚动时导航栏都会重新出现？

Answer 1

我已经为这个更直观的代码废弃了手动框架代码：

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if (lastContentOffset > scrollView.contentOffset.y) {
        if (downwards) {
            downwards = NO;
            scrollDistance = 0;
        } else {
            scrollDistance++;
        }
    }
    else if (lastContentOffset < scrollView.contentOffset.y) {
        if (!downwards) {
            downwards = YES;
            scrollDistance = 0;
        } else {
            scrollDistance++;
        }
    }
    lastContentOffset = scrollView.contentOffset.y;
    CGFloat threshold = 10;
    if (downwards && !self.navigationController.navigationBarHidden && scrollDistance > threshold) {
        [self.navigationController setNavigationBarHidden:YES animated:YES];
    } else if (!downwards && self.navigationController.navigationBarHidden && scrollDistance > threshold) {
        [self.navigationController setNavigationBarHidden:NO animated:YES];
    }

}

这也增加了一个 10px 的阈值，以便它只对有意义的向上或向下滚动做出反应

Answer 2

使用此链接检测滚动方向：Detect Scroll Direction

我真的不明白你在用你发布的代码做什么。您是每次都创建一个新的导航栏还是隐藏和显示同一个导航栏？

无论如何，一旦检测到滚动方向，只需在ScrollDirection = ScrollDirectionUp 时显示导航栏。

类似：

if (ScrollDirection == ScrollDirectionUp) {
    self.navigationController.navigationBar.hidden = NO;
}