尝试基于WKWebView中的当前URL在外部打开PDF，但未触发decidePolicyForNavigationAction

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {
    var webView: WKWebView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let configuration = WKWebViewConfiguration()
        configuration.preferences.allowFileAccessFromFileURLs = true
        configuration.preferences.allowUniversalAccessFromFileURLs = true
        
        webView = WKWebView(frame: view.bounds, configuration: configuration)
        webView.navigationDelegate = self
        view.addSubview(webView)
        
        if let url = URL(string: "https://example.com/path/to/pdf.pdf") {
            let request = URLRequest(url: url)
            webView.load(request)
        }
    }
    
    // WKNavigationDelegate方法
    func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
        // 在这里处理导航行为，例如判断是否是PDF文件并在外部打开
        if let url = navigationAction.request.url, url.absoluteString.hasSuffix(".pdf") {
            UIApplication.shared.open(url, options: [:], completionHandler: nil)
            decisionHandler(.cancel)
            return
        }
        
        decisionHandler(.allow)
    }
}