[self.navigationController setNavigationBarHidden:NO animated:animated];
[self.navigationController.navigationBar setBackgroundImage:[UIImage createImageWithColor:[UIColor colorWithHexString:@"#F6F7F9"]] forBarMetrics:UIBarMetricsDefault];

if (@available(iOS 13.0, *)) {
    UINavigationBarAppearance *appearance = [[UINavigationBarAppearance alloc] init];
    appearance.backgroundColor = [UIColor colorWithHexString:@"#F6F7F9"]; //背景色
    appearance.shadowColor = UIColor.clearColor; //阴影
    self.navigationController.navigationBar.standardAppearance = appearance;
    self.navigationController.navigationBar.scrollEdgeAppearance = appearance;
}

• (UIImage )createImageWithColor:(UIColor)color {
  CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
  UIGraphicsBeginImageContext(rect.size);
  CGContextRef context = UIGraphicsGetCurrentContext();
  CGContextSetFillColorWithColor(context, [color CGColor]);
  CGContextFillRect(context, rect);
  UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return theImage;
  }