ios - 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，但导航只会在您滚动到 ScrollView 的顶部时重新出现(y 偏移量 = 0)。我怎样才能重现 Instagram 的行为，每当您向上滚动时，导航栏就会重新出现？

Answer 1

我已经放弃了这个更直观的代码的手动框架代码:

- (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];
    }

}

这还添加了一个 10px 的阈值，以便它只对有意义的向上或向下滚动使用react