如何优雅的给navigationBar添加背景图片

• navigationBar 设置背景图片的方法

  self.navigationController?.navigationBar .setBackgroundImage(barImage, for: .default)
  

// 固定的图片会导致在不同机型上面变形所以我们需要自己创建uiimage对象并保存到本地

/// 创建APPBar 的背景图片 避免各机型不一致导致图片变形
/// - Returns: appbar 背景图片
static func creatNavigationBarGradientImageWithColors() -> UIImage {
    let  size = CGSize.init(width: KSCREENWIDHT, height: KNavigationHeight)
    let colors = [UIColor.red,UIColor.yellow]
    if colors.count == 0 || size == CGSize.zero {
        return UIImage.init()
    }

    // 主要图层
    let gradientLayer = CAGradientLayer.init()
    gradientLayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    gradientLayer.startPoint = CGPoint(x: 0, y: 0);
    gradientLayer.endPoint = CGPoint(x: 1, y: 0);
    var cgColors = [CGColor]()
    colors.forEach { (color) in
        cgColors.append(color.cgColor)
    }
    gradientLayer.colors = cgColors
    
    // 其他小icon
    let imageView = UIImageView.init(frame: CGRect(x: 100, y: size.height-44, width: 44, height: 44))
    imageView.image = KHeadImage
    gradientLayer.addSublayer(imageView.layer)
    
    
    UIGraphicsBeginImageContextWithOptions(gradientLayer.frame.size, gradientLayer.isOpaque, 0);
    gradientLayer.render(in: UIGraphicsGetCurrentContext()!)
    guard let outPutImage =  UIGraphicsGetImageFromCurrentImageContext() else {
        UIGraphicsEndImageContext();
        return UIImage()
    };
    UIGraphicsEndImageContext();
    
    return outPutImage
}