ios - 如何确保 WidgetKit 视图显示来自 @FetchRequest 的正确结果?
问题描述
我有一个将 Core Data 与 CloudKit 一起使用的应用程序。更改在设备之间同步。主要目标具有背景模式功能,并带有选中的远程通知。主要目标和小部件目标都具有相同的应用程序组,并且都具有 iCloud 功能,服务设置为 CloudKit,并且容器中的相同容器已选中。
我的目标是在 SwiftUI WidgetKit 视图中显示实际的核心数据条目。
我的小部件目标文件:
import WidgetKit
import SwiftUI
import CoreData
// MARK: For Core Data
public extension URL {
/// Returns a URL for the given app group and database pointing to the sqlite database.
static func storeURL(for appGroup: String, databaseName: String) -> URL {
guard let fileContainer = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: appGroup) else {
fatalError("Shared file container could not be created.")
}
return fileContainer.appendingPathComponent("\(databaseName).sqlite")
}
}
var managedObjectContext: NSManagedObjectContext {
return persistentContainer.viewContext
}
var workingContext: NSManagedObjectContext {
let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
context.parent = managedObjectContext
return context
}
var persistentContainer: NSPersistentCloudKitContainer = {
let container = NSPersistentCloudKitContainer(name: "Countdowns")
let storeURL = URL.storeURL(for: "group.app-group-countdowns", databaseName: "Countdowns")
let description = NSPersistentStoreDescription(url: storeURL)
container.loadPersistentStores(completionHandler: { storeDescription, error in
if let error = error as NSError? {
print(error)
}
})
container.viewContext.automaticallyMergesChangesFromParent = true
container.viewContext.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy
return container
}()
// MARK: For Widget
struct Provider: TimelineProvider {
var moc = managedObjectContext
init(context : NSManagedObjectContext) {
self.moc = context
}
func placeholder(in context: Context) -> SimpleEntry {
return SimpleEntry(date: Date())
}
func getSnapshot(in context: Context, completion: @escaping (SimpleEntry) -> ()) {
let entry = SimpleEntry(date: Date())
return completion(entry)
}
func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {
var entries: [SimpleEntry] = []
let currentDate = Date()
for hourOffset in 0 ..< 5 {
let entryDate = Calendar.current.date(byAdding: .minute, value: hourOffset, to: currentDate)!
let entry = SimpleEntry(date: entryDate)
entries.append(entry)
}
let timeline = Timeline(entries: entries, policy: .atEnd)
completion(timeline)
}
}
struct SimpleEntry: TimelineEntry {
let date: Date
}
struct CountdownsWidgetEntryView : View {
var entry: Provider.Entry
@FetchRequest(entity: Countdown.entity(), sortDescriptors: []) var countdowns: FetchedResults<Countdown>
var body: some View {
return (
VStack {
ForEach(countdowns, id: \.self) { (memoryItem: Countdown) in
Text(memoryItem.title ?? "Default title")
}.environment(\.managedObjectContext, managedObjectContext)
Text(entry.date, style: .time)
}
)
}
}
@main
struct CountdownsWidget: Widget {
let kind: String = "CountdownsWidget"
var body: some WidgetConfiguration {
StaticConfiguration(kind: kind, provider: Provider(context: managedObjectContext)) { entry in
CountdownsWidgetEntryView(entry: entry)
.environment(\.managedObjectContext, managedObjectContext)
}
.configurationDisplayName("My Widget")
.description("This is an example widget.")
}
}
struct CountdownsWidget_Previews: PreviewProvider {
static var previews: some View {
CountdownsWidgetEntryView(entry: SimpleEntry(date: Date()))
.previewContext(WidgetPreviewContext(family: .systemSmall))
}
}
但我有一个问题:假设我Countdown
在主应用程序中有 3 条记录:
在开始时,小部件视图在预览中显示 3 条记录(用于添加小部件的 UI)。但是在我将一个小部件添加到主屏幕后,它不显示Countdown
行,只显示entry.date, style: .time
. 当时间线条目更改时,行也不可见。我做了一张图片来更好地说明这一点:
或者:
Countdown
在开始小部件视图按预期显示 3 条记录,但大约一分钟后,如果我在主应用程序中删除或添加记录,小部件仍显示初始 3 值,但我希望它显示实际值数(以反映变化)。时间线entry.date, style .time
更改,反映在小部件中,但不是来自请求的条目。
有什么方法可以确保我的小部件显示正确的获取请求结果?谢谢。
解决方案
小部件视图不会观察到任何东西。他们只是提供TimelineEntry
数据。这意味着@FetchRequest
,@ObservedObject
等在这里不起作用。
- 为您的容器启用远程通知:
let container = NSPersistentContainer(name: "DataModel")
let description = container.persistentStoreDescriptions.first
description?.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
- 更新您的 CoreDataManager 以观察远程通知:
class CoreDataManager {
var itemCount: Int?
private var observers = [NSObjectProtocol]()
init() {
fetchData()
observers.append(
NotificationCenter.default.addObserver(forName: .NSPersistentStoreRemoteChange, object: nil, queue: .main) { _ in
// make sure you don't call this too often - notifications may be posted in very short time frames
self.fetchData()
}
)
}
deinit {
observers.forEach(NotificationCenter.default.removeObserver)
}
func fetchData() {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Item")
do {
self.itemCount = try CoreDataStack.shared.managedObjectContext.count(for: fetchRequest)
WidgetCenter.shared.reloadAllTimelines()
} catch {
print("Failed to fetch: \(error)")
}
}
}
- 在 中添加另一个字段
Entry
:
struct SimpleEntry: TimelineEntry {
let date: Date
let itemCount: Int?
}
- 将其全部用于
Provider
:
struct Provider: TimelineProvider {
let coreDataManager = CoreDataManager()
...
func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> Void) {
let entries = [
SimpleEntry(date: Date(), itemCount: coreDataManager.itemCount),
]
let timeline = Timeline(entries: entries, policy: .never)
completion(timeline)
}
}
- 现在您可以在视图中显示您的条目:
struct WidgetExtEntryView: View {
var entry: Provider.Entry
var body: some View {
VStack {
Text(entry.date, style: .time)
Text("Count: \(String(describing: entry.itemCount))")
}
}
}
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