你如何设置UIPopoverController的内容大小？

import UIKit

class CustomContentViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // 设置视图的大小
        let customSize = CGSize(width: 320, height: 480)
        preferredContentSize = customSize
    }
}

class MainViewController: UIViewController, UIPopoverPresentationControllerDelegate {

    // 创建并显示UIPopoverController
    func showPopover() {
        // 创建自定义内容视图控制器
        let customContentViewController = CustomContentViewController()

        // 创建UIPopoverController
        let popoverController = UIPopoverController(contentViewController: customContentViewController)

        // 设置代理
        popoverController.delegate = self

        // 显示UIPopoverController
        popoverController.present(from: CGRect(x: view.bounds.midX, y: view.bounds.midY, width: 0, height: 0), in: view, permittedArrowDirections: [.up, .down], animated: true)
    }

    // 实现代理方法
    func adaptivePresentationStyle(for controller: UIPresentationController) -> UIModalPresentationStyle {
        return .none
    }
}