如何固定UILabel位置?

尝试以下操作:

@interface ViewController () <UIScrollViewDelegate>

@property (nonatomic, weak) IBOutlet UILabel *fadingLabel;

@end

@implementation ViewController

#pragma mark - UIScrollViewDelegate

/* For this method to get called, make sure you set the delegate of your table view to this view controller.*/

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (!self.fadingLabel)
        return;

    CGFloat labelHeight = CGRectGetHeight(self.fadingLabel.frame);
    CGFloat alpha = 1.0f - (scrollView.contentOffset.y / labelHeight);
    [self.fadingLabel setAlpha:alpha];
}

@end

以下是快速翻译:

class ViewController: UIViewController, UIScrollViewDelegate {
    private weak var fadingLabel: UILabel?

    // MARK: - UIScrollViewDelegate

    /* For this method to get called, make sure you set the delegate of your table view to this view controller.*/
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        guard let label = self.fadingLabel else {
            return
        }

        let labelHeight: CGFloat = label.frame.height
        let alpha: CGFloat = 1.0 - (scrollView.contentOffset.y / labelHeight)
        label.alpha = alpha
    }
}

您应该实施 UIScrollViewDelegate 并根据中滚动视图的垂直内容偏移隐藏/显示标签 scrollViewDidScroll(_:) 。

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    label.isHidden = scrollView.contentOffset.y > 50
}

不要忘记设置滚动视图的代理:

scrollView.delegate = self