Question

使用Xcode macOS Document App模板创建项目，并选中Use Core Data复选框。
将图书实体添加到Document.xcdatamodeld
将FetchRequest扭曲属性添加到ContentView，

@FetchRequest(entity: Book.entity(), sortDescriptors: []) var books: FetchedResults<Book>

构建并运行，崩溃！

控制台的崩溃日志为

2020-07-03 23:12:23.597880+0800 DocMacDemo[15236:4376209] [error] error: No NSEntityDescriptions in any model claim the NSManagedObject subclass 'DocMacDemo.Book' so +entity is confused.  Have you loaded your NSManagedObjectModel yet ?
CoreData: error: No NSEntityDescriptions in any model claim the NSManagedObject subclass 'DocMacDemo.Book' so +entity is confused.  Have you loaded your NSManagedObjectModel yet ?
2020-07-03 23:12:23.598287+0800 DocMacDemo[15236:4376209] [error] error: +[DocMacDemo.Book entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass
CoreData: error: +[DocMacDemo.Book entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass
2020-07-03 23:12:23.644491+0800 DocMacDemo[15236:4376209] executeFetchRequest:error: A fetch request must have an entity.
2020-07-03 23:12:23.653769+0800 DocMacDemo[15236:4376209] [error] error: The fetch request's entity 0x600003500420 'Book' appears to be from a different NSManagedObjectModel than this context's
CoreData: error: The fetch request's entity 0x600003500420 'Book' appears to be from a different NSManagedObjectModel than this context's
(lldb)

几天来我一直在寻找NSPersistentDocument SwiftUI示例，但找不到。这是一些相似或相关的问题。不幸的是，这个问题没有解决。

编辑：将此问题项目上载到Github，https://github.com/donly/DocMacDemo。

Answer 1

这是由于新文档为空。像在任何基于文档的应用程序中一样，您必须为新文档准备一些默认的初始数据

这是可能的解决方案。使用Xcode 11.4 / iOS 13.4进行了测试

在Document.swift中

class Document: NSPersistentDocument {

    // .. other code here

    override func makeWindowControllers() {

        // in case of new document create new empty book in context
        // that will be shown in opened document window
        let isNew = self.fileURL == nil
        if isNew {
            _ = Book(context: self.managedObjectContext!)       // << here !!
        }

        let contentView = ContentView().environment(\.managedObjectContext, self.managedObjectContext!)

        // ... other code here

Answer 2

好吧，Asperi 的答案很好，但是这给您留下了对象模型中可能不需要的 Book。另一种方法是将上下文保存在 Asperi 建议的同一位置：

    if let context = managedObjectContext {
        try? context.save()
    }

那么 FetchRequest 也不会出现错误信息。

macOS Document App SwiftUI项目上的NSPersistentDocument FetchRequest翘曲属性崩溃

2 个答案: