KVO监测tableView的滑动

[self.tableView addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew context:nil];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
    
    NSLog(@"%f",self.tableView.contentOffset.y);
    
    CGFloat offset = self.tableView.contentOffset.y;
    CGFloat delta = offset/64.f + 0.5;
    
    NSLog(@"===============%f",offset/64.f);
    
    delta = MAX(0, delta);
    self.navigationController.navigationBar.alpha = MIN(delta,1);
}

#define RGBACOLOR(r, g, b, a)   [UIColor colorWithRed:(r)/255.0f green:(g)/255.0f blue:(b)/255.0f alpha:(a)]

self.navigationController.navigationBar.barTintColor = RGBACOLOR(36, 188, 61, 10);
self.navigationController.navigationBar.tintColor = [UIColor whiteColor];
self.navigationController.navigationBar.barStyle = UIStatusBarStyleDefault;