如何使用Swift语言显示AdMob应用程序打开的广告？

import GoogleMobileAds

class ViewController: UIViewController, GADBannerViewDelegate {
    var bannerView: GADBannerView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        bannerView = GADBannerView(adSize: kGADAdSizeBanner)
        bannerView.adUnitID = "YOUR_AD_UNIT_ID"
        bannerView.rootViewController = self
        bannerView.delegate = self
        
        let request = GADRequest()
        request.testDevices = [kGADSimulatorID] // 在模拟器上测试广告
        
        bannerView.load(request)
    }
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    
    let adHeight = bannerView.frame.size.height
    let adWidth = bannerView.frame.size.width
    let screenWidth = view.frame.size.width
    let screenHeight = view.frame.size.height
    
    bannerView.frame = CGRect(x: (screenWidth - adWidth) / 2, y: screenHeight - adHeight, width: adWidth, height: adHeight)
    
    view.addSubview(bannerView)
}

func adViewDidReceiveAd(_ bannerView: GADBannerView) {
    print("广告加载成功")
}

func adView(_ bannerView: GADBannerView, didFailToReceiveAdWithError error: GADRequestError) {
    print("广告加载失败: \(error.localizedDescription)")
}

func adViewWillPresentScreen(_ bannerView: GADBannerView) {
    print("广告将要显示全屏广告")
}

func adViewWillDismissScreen(_ bannerView: GADBannerView) {
    print("广告将要关闭全屏广告")
}

func adViewDidDismissScreen(_ bannerView: GADBannerView) {
    print("广告已关闭全屏广告")
}

func adViewWillLeaveApplication(_ bannerView: GADBannerView) {
    print("用户点击广告将离开应用")
}