如何调整UIImageView与矢量图适配缩放，避免图像模糊

我在资产目录中有一个名为Link的矢量图（PDF格式，已设置保留矢量数据），用UIImageView展示的代码如下：

let image = UIImage(named: "Link")
let imageView = UIImageView()
imageView.contentMode = .scaleAspectFit
imageView.image = image

当前视图层级结构：[view hierarchy]

使用.scaleAspectFit时，只要设置好imageView的frame，图像就能以对应分辨率清晰渲染，目前显示正常。但加入UIScrollView实现缩放滚动后，放大图像会出现分辨率不足导致的模糊：[放大后模糊的图像]

是否有简便方法调整UIImageView，使其以更高分辨率渲染图像？

现有思路讨论 #

• 使用.scaleAspectFit时，图像渲染分辨率依赖于imageView的frame大小。设置更大的frame再通过transform缩放视图可以解决问题，但操作繁琐。
• 另一种方法是用UIGraphicsImageRenderer等工具从矢量图手动渲染对应分辨率的图像，这是目前首选方案，但想知道有没有更简便的基于UIImageView的实现方式。

示例代码 #

在新项目中替换主ViewController即可运行（需准备名为Link的矢量图并设置为“Template Image”）：

class ViewController: UIViewController, UIScrollViewDelegate {
    let contentView: UIView = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 1000.0, height: 1000.0))
    let scrollView: UIScrollView = {
        let view = UIScrollView(frame: CGRect(x: 0.0, y: 0.0, width: 400.0, height: 400.0))
        view.minimumZoomScale = 0.5
        view.maximumZoomScale = 10.0
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.scrollView.delegate = self
        
        self.contentView.backgroundColor = UIColor.green.withAlphaComponent(0.2)
        
        // setup view hierarchy
        self.scrollView.translatesAutoresizingMaskIntoConstraints = false
        self.contentView.translatesAutoresizingMaskIntoConstraints = false
        self.view.addSubview(self.scrollView)
        self.scrollView.addSubview(self.contentView)
        // constraints
        self.scrollView.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
        self.scrollView.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true
        self.scrollView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
        self.scrollView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
        self.contentView.leftAnchor.constraint(equalTo: self.scrollView.leftAnchor).isActive = true
        self.contentView.rightAnchor.constraint(equalTo: self.scrollView.rightAnchor).isActive = true
        self.contentView.topAnchor.constraint(equalTo: self.scrollView.topAnchor).isActive = true
        self.contentView.bottomAnchor.constraint(equalTo: self.scrollView.bottomAnchor).isActive = true
        self.contentView.widthAnchor.constraint(equalToConstant: 10.0 * self.view.frame.width).isActive = true
        self.contentView.heightAnchor.constraint(equalToConstant: 10.0 * self.view.frame.height).isActive = true
        
        // setup imageView
        let image = UIImage(named: "Link")
        let imageView = UIImageView()
        imageView.contentMode = .scaleAspectFit
        imageView.image = image
        imageView.tintColor = UIColor.black
        imageView.translatesAutoresizingMaskIntoConstraints = false
        self.contentView.addSubview(imageView)
        // add constraints
        imageView.centerXAnchor.constraint(equalTo: self.contentView.centerXAnchor).isActive = true
        imageView.centerYAnchor.constraint(equalTo: self.contentView.centerYAnchor).isActive = true
        imageView.widthAnchor.constraint(equalToConstant: 100.0).isActive = true
        imageView.heightAnchor.constraint(equalToConstant: 100.0).isActive = true
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        let zoomScale = 8.0
        self.scrollView.contentOffset = CGPoint(x: 0.5 * (self.contentView.frame.width - self.scrollView.frame.width), y: 0.5 * (self.contentView.frame.height - self.scrollView.frame.height))
        self.scrollView.zoomScale = zoomScale
    }
    
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return self.contentView
    }
}

内容的提问来源于stack exchange，提问作者Wizard