AppDelegate.Swift 更新到 Swift 5 后编译错误

Question

我最近更新了一个项目，一两年没碰它，现在我遇到了一些问题。

之前一切正常，我什至通过每个错误来更新新语法，但我被困在 AppDelegate.Swift 中的一个函数，这阻止了我运行该程序。就是这个：

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = Bundle.mainBundle.url(forResource: "ProjectName", withExtension: "momd")
    return NSManagedObjectModel(contentsOfURL: modelURL ?? <#default value#>)!
}()

在我采纳 Xcode 的建议并更新语法后，它看起来像这样：

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = Bundle.main.url(forResource: "ProjectName", withExtension: "momd")
    return NSManagedObjectModel(contentsOf: modelURL ?? <#default value#>)!
}()

对于 默认值 应该设置什么，我真的很困惑，因为我以前从未编辑或接触过 AppDelegate。我需要在这里放什么？

感谢您提供的任何帮助！

Answer 1

如果模型丢失，应用程序根本无法运行，您可以强制解包 URL

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = Bundle.main.url(forResource: "ProjectName", withExtension: "momd")!
    return NSManagedObjectModel(contentsOf: modelURL)!
}()

考虑自 iOS 10，macOS 10.12 有一个 more convenient way to initialize the Core Data stack with NSPersistentContainer

AppDelegate.Swift 更新到 Swift 5 后编译错误

AppDelegate.Swift compile error after updating to Swift 5

swift

xcode

swift5

appdelegate