DispatchGroup 和领域

Question

我的应用程序使用 Swift 3.1、Realm 2.7.0 作为数据库，并有一个后台服务使用 DispatchGroup 来控制我确定的进程的流程。

首先，在我的 ViewController 中，我实现了 Realm 的通知系统，称为 NotificationToken，它使用方法 addNotificationBlock 来检测确定对象中数据的任何变化。

到那时，一切正常。所有更改都会调用此块。

我实现了一个使用一堆 DispatchQueue 和 DispatchGroup 的新流程，这里是一个例子：

这段代码只是一个示例！不要这样做！

DispatchQueue.global(qos: .background).async {

  autoreleasepool {

    //Other stuff...

    let id = 1337
    let dispatchGroup = DispatchGroup()

    dispatchGroup.enter()
    DispatchQueue(label: "Process").sync {

      let foo = Bar()

      foo.progress = { newValueInt in
        let realm = try! Realm()
        try! realm.write {
          realm
            .object(ofType: Some.self, forPrimaryKey: id)
            .someValue = newValueInt
        }
      }

      foo.completed = {
        dispatchGroup.leave()
      }

      foo.doSomethingAsync()

    }

    dispatchGroup.notify(queue: DispatchQueue.global(qos: .background)) {
      //Process completed.
    }

  }

}

问题是：当方法 Bar.progress 运行时，addNotificationBlock 未被调用，添加到其通知块中的对象未更新。

谢谢！

Answer 1

解决方法很简单，只需要在主线程运行更新即可。

foo.progress = { newValueInt in
    DispatchQueue.main.sync {
      let realm = try! Realm()
      try! realm.write {
        realm
          .object(ofType: Some.self, forPrimaryKey: id)
          .someValue = newValueInt
      }
    }
  }

Answer 2

这是一个完整的应用程序，它使用您的代码，填充了您未提供的空白，并且正确调用了通知块：

import UIKit
import RealmSwift

class Bar {
    var progress: ((Int) -> Void)?
    var completed: (() -> Void)?

    func doSomethingAsync() {
        for delay in 1...100 {
            // Span these 100 updates over 10 seconds
            DispatchQueue.global(qos: .background).asyncAfter(deadline: .now() + Double(delay) / 10) {
                self.progress?(delay)
                if delay == 100 {
                    self.completed?()
                }
            }
        }
    }

    init() {}
}

class Some: Object {
    dynamic var id = 0
    dynamic var someValue = 0

    override static func primaryKey() -> String? {
        return "id"
    }
}

func bgTask() {
    DispatchQueue.global(qos: .background).async {
        autoreleasepool {

            //Other stuff...

            let id = 1337
            let dispatchGroup = DispatchGroup()

            dispatchGroup.enter()
            DispatchQueue(label: "Process").sync {
                let foo = Bar()
                foo.progress = { newValueInt in
                    let realm = try! Realm()
                    try! realm.write {
                        realm
                            .object(ofType: Some.self, forPrimaryKey: id)!
                            .someValue = newValueInt
                    }
                }
                foo.completed = {
                    dispatchGroup.leave()
                }
                foo.doSomethingAsync()
            }
            dispatchGroup.notify(queue: .global(qos: .background)) {
                //Process completed.
            }
        }
    }
}

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    var notificationToken: NotificationToken!

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        _ = try? FileManager.default.removeItem(at: Realm.Configuration.defaultConfiguration.fileURL!)
        let realm = try! Realm()
        let some = Some()
        try! realm.write {
            some.id = 1337
            realm.add(some)
        }
        notificationToken = some.addNotificationBlock { change in
            switch change {
            case .change(let properties):
                print(properties)
            case .error(let error):
                print("An error occurred: \(error)")
            case .deleted:
                print("The object was deleted.")
            }
        }
        bgTask()
        return true
    }
}

此日志（为简洁起见被截断）：

[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(0), newValue: Optional(1))]
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(1), newValue: Optional(2))]
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(2), newValue: Optional(3))]
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(3), newValue: Optional(4))]
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(4), newValue: Optional(5))]
...
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(98), newValue: Optional(97))]
[RealmSwift.PropertyChange(name: "someValue", oldValue: Optional(97), newValue: Optional(100))]

DispatchGroup 和领域

DispatchGroup and Realm

background-process

realm

grand-central-dispatch

ios

swift