效果圖.gif

直接上代碼：

- (void)viewDidLoad {
    [super viewDidLoad];
    ///iOS 15更新后，導(dǎo)航欄變白茸歧，靜止情況看不清
    if (@available(iOS 13.0, *)) {
        UINavigationBarAppearance *appearance = [UINavigationBarAppearance new];
        [appearance configureWithOpaqueBackground];
        appearance.backgroundColor = [UIColor purpleColor];
        self.navigationController.navigationBar.standardAppearance = appearance;
        self.navigationController.navigationBar.scrollEdgeAppearance = self.navigationController.navigationBar.standardAppearance;
    } else {
        // Fallback on earlier versions
    }
    
    self.navigationController.navigationBar.translucent = YES;
    self.navigationController.navigationBar.subviews[0].alpha = 0;

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    // 設(shè)置導(dǎo)航欄為透明倦炒，并根據(jù)當(dāng)前tableView的偏移量設(shè)置對應(yīng)的 alpha
    self.navigationController.navigationBar.translucent = YES;
    [self setNavigationBarColorWithOffsetY:self.table.contentOffset.y];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    // 設(shè)置導(dǎo)航欄 為不透明
    self.navigationController.navigationBar.translucent = NO;
    self.navigationController.navigationBar.subviews[0].alpha = 1.0;
}

//監(jiān)聽scrollView滑動
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView == self.table) {
        CGFloat offsetY = scrollView.contentOffset.y;
        [self setNavigationBarColorWithOffsetY:offsetY];
    }
}

// 界面滑動時導(dǎo)航欄隨偏移量 實時變化
- (void)setNavigationBarColorWithOffsetY:(CGFloat)offsetY {
    UIImageView *backView = self.navigationController.navigationBar.subviews[0];
    if (offsetY <= 0) {
        backView.alpha = 0;
        self.lab.textColor = [UIColor redColor]; //這里可以根據(jù)UI設(shè)置導(dǎo)航欄上的控件顯示的顏色
    } else if (offsetY > 0 && offsetY < 91) {
        backView.alpha = offsetY / 91;
    } else if (offsetY >= 91 ) {//&& offsetY <= NavBar_HEIGHT + 30
        backView.alpha = 1;
        self.lab.textColor = [UIColor yellowColor]; //這里可以根據(jù)UI設(shè)置導(dǎo)航欄上的控件顯示的顏色
    }
}

這是一種實現(xiàn)方法，另一種可以使用kvo監(jiān)聽 contentOffset.y 也可以實現(xiàn)软瞎。
需要寫上

superScrollView .addObserver(self, forKeyPath: "contentOffset", options: NSKeyValueObservingOptions(rawValue: 0), context: nil)

然后逢唤，再監(jiān)聽回調(diào)中，實現(xiàn)導(dǎo)航漸變