无法访问 MTKView

Question

我是 UIKit 的新手，我正在尝试在 iPhone 12 上为运行编写一个 Metal 应用程序。这是 AppDelegate.swift 中的代码：

class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        window = UIWindow(frame: UIScreen.main.bounds)
        window?.rootViewController = ViewController()
        window?.makeKeyAndVisible()
        return true
    }
}

这是 ViewController.swift 中的代码：

class ViewController: UIViewController, MTKViewDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()

        // Access the Metal view
        if let view = self.view! as? MTKView {  // Isn't working
            view.device = MTLCreateSystemDefaultDevice()
            view.delegate = self
            print("Obtained MTKView")
        } else {
            print("Failed to obtain MTKView")   // The result
        }
    }
    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}
    func draw(in view: MTKView) {}
}

此代码编译运行，但它不访问 MTKView。它打印 Failed to obtain MTKView 消息。有任何想法吗？谢谢。

编辑：我试过 self.view! 和 self.view，但都没有用。

Answer 1

如果您不使用情节提要，可以像这样创建一个新的 MTKView：

class ViewController: UIViewController, MTKViewDelegate {

    var metalView: MTKView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        /// Make a MetalKit view
        let metalView = MTKView()
            
        /// add positioning constraints
        metalView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            metalView.topAnchor.constraint(equalTo: view.topAnchor),
            metalView.rightAnchor.constraint(equalTo: view.rightAnchor),
            metalView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            metalView.leftAnchor.constraint(equalTo: view.leftAnchor)
        ])
        
        metalView.device = MTLCreateSystemDefaultDevice()
        metalView.delegate = self
        
        self.metalView = metalView /// assign to the property, so you can access this later
    }

    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}
    func draw(in view: MTKView) {}
}

无法访问 MTKView

Can't access MTKView

uikit

swift

metal