UIImage。draw()函数在viewDidLoad()回调中不工作[已关闭]

在 viewDidLoad() 在下面的回调中,为什么 image?.draw()

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let image = UIImage(named:"0")
        image?.draw(in: CGRect(x: 0, y: 0, width: 100, height: 100))
    }

    // more code here
}