从 iOS 14 小部件的 CoreData 获取数据 [英] Fetch data from CoreData for iOS 14 widget

问题描述

我想在小部件中显示从 Core Data 获取的数据.但是 @FetchRequest 不适用于小部件.

I want to display data fetched from Core Data in a widget. But @FetchRequest doesn’t work on widgets.

据我所知，我们必须创建一个应用程序组并创建一个共享的持久容器.

As I understand, we have to create an app group and make a shared persistent container.

我想知道的是如何从共享的持久容器读取(获取)小部件上的数据，或者简单地说，如何在小部件中显示从核心数据获取的数据.

What I want to know is how to read (fetch) data on widgets from that shared persistent container or simply, how to display data fetched from Core Data in widgets.

推荐答案

首先您需要创建一个 AppGroup，它将用于创建一个 Core Data Persistent Container (这里 是一个很好的解释)

First you need to create an AppGroup which will be used to create a Core Data Persistent Container (here is a good explanation how to do it)

然后您需要创建自己的 CoreData 堆栈(创建一个启用 CoreData 的新空项目时可以找到示例).

Then you need to create your own CoreData stack (an example can be found when you create a new empty project with CoreData enabled).

• 在 MVVM 应用程序中访问核心数据堆栈

假设您已经创建了 Core Data 模型(此处称为 DataModel)，您现在需要将容器 url 设置为您自定义的共享容器位置:

Assuming you have already created your Core Data model (here called DataModel), you now need to set the container url to your custom shared container location:

• 在 iOS 14 的 SwiftUI 中在主应用程序和小部件之间共享数据

let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: <your_app_group>)!
let storeURL = containerURL.appendingPathComponent("DataModel.sqlite")
let description = NSPersistentStoreDescription(url: storeURL)

let container = NSPersistentContainer(name: "DataModel")
container.persistentStoreDescriptions = [description]
container.loadPersistentStores { ... }

现在您可以从共享的 Persistent Container 中获取 managedObjectContext:

Now you can get the managedObjectContext from your shared Persistent Container:

let moc = CoreDataStack.shared.managedObjectContext

并使用它执行获取请求(更多信息此处)

and perform a fetch request with it (more information here)

let predicate = NSPredicate(format: "attribute1 == %@", "test")
let request = NSFetchRequest<SomeItem>(entityName: "SomeItem")
let result = try moc.fetch(request)

除了上面的所有链接，我还建议您阅读有关 Core Data 的教程:

Apart from all the links above I recommend you also read this tutorial about Core Data:

• 核心数据与 SwiftUI 教程:入门

_这是一个 GitHub 存储库，其中包含不同的 Widget 示例，包括核心数据小部件.

_{Here is a GitHub repository with different Widget examples including the Core Data Widget.}

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