Swift Firebase - 如何从 GeoFire 获取单个用户的位置

Question

1- 我的应用中的所有用户每 2.5 分钟使用 Timer 将他们的位置发送到 GeoFire。

2- 其他用户也会查询 GeoFire 以查找距离他们 1 英里半径内的任何用户（例如 10 个用户）。我得到这 10 个用户，然后将它们添加到一个数组中。

3- 然后，我使用这 10 个用户的 userId（geoRef 键）循环遍历数组。我去他们的数据库参考并搜索以查看它们是否符合某些标准。如果他们这样做，我将它们添加到不同的数组中（例如，现在这个子集数组中有 5 个用户）

4- 由于每 2.5 分钟将每个用户的位置发送到 GeoFire，这意味着该子集中的这 5 个用户的位置可能与他们首次添加到子集数组时的位置不同。

我可以使用计时器来查询这 5 个用户的位置。问题是我如何查询 GeoFire 以仅从这 5 个用户中获取每个用户的位置？我不想再次查询该 1 英里区域内的每个人，否则它会让我得到相同的结果10 个用户

// I have a Timer firing this off
func queryLocationOfSubsetOfUsersInRadius() {

    let geofireRef = Database.database().reference().child("geoLocations")
    let geoFire = GeoFire(firebaseRef: geoFireRef)

    let dispatchGroup = DispatchGroup()

    for user in subsetOfUsersInRadius {

        dispatchGroup.enter()

        let userId = user.userId

        // I don't know if this is the right method to use. I only added it here because I saw it has observeValue on it
        geoFire.observeValue(forKeyPath: userId, of: Any?, change: NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?)

            // *** HOW TO GET THE USERS NEW LOCATION and use dispatchGroup.leave() as each one is obtained??? ***

            dispatchGroup.leave()
    }

    dispatchGroup.notify(queue: .global(qos: .background)) {

       // now animate the annotation from the user's inital old location (if they moved) on the mapView to their new location on the mapView. It's supposed to look like Uber's cars moving. Happens on main thread
    }
}

下面的支持代码

var queryHandle: UInt?
var regionQuery: GFRegionQuery?

var usersInRadius = [User]() // has 10 users
var subsetOfUsersInRadius = [User]() // of the 10 only 5 fit some criteria

let geofireRef = Database.database().reference().child("geoLocations")
let geoFire = GeoFire(firebaseRef: geofireRef)

// region: MKCoordinateRegion was previously set at 1 mile 1609.344 meters

regionQuery = geoFire.query(with: region)
queryHandle = regionQuery?.observe(.keyEntered, with: { [weak self](key: String!, location: CLLocation!) in

    let user = User()
    user.userId = key
    user.location = location

    self?.usersInRadius.append(user)
})

regionQuery?.observeReady({ [weak self] in

    self?.sortUsersInRadius(arr: self!.usersInRadius)
})

func sortUsersInRadius(arr: [User]) {

    if let queryHandle = queryHandle {
        regionQuery?.removeObserver(withFirebaseHandle: queryHandle)
    }

    let dispatchGroup = DispatchGroup()

    for user in arr {

        let userId = user.userId

        someDatabaseRef.child(userId).observeSingleEvent(of: .value, with: { (snapshot) in

             // if snapshot contains some critera add that user to the subSet array

             self?.subsetOfUsersInRadius.append(user) // only 5 users fit this criteria

             dispatchGroup.leave()
        })
    }

    dispatchGroup.notify(queue: .global(qos: .background)) {

       // add an annotation to mapView to show the initial location of each user from subsetOfUsersInRadius. Happens on main thread
    }
}

Answer 1

在数据库中，每个 userId 位置的 GeoFire ref 都有一个 "g" 孩子和一个 "l" 孩子：

@geoLocations
      |
      @--abc123xyz456 // userId
           |
           @--g: "dr72xyz25abc" // geoFire id for this user's location in geoFire
           |
           @--l
              |--0: 40.870431300779900 // latitude
              |--1: -73.090007211987188 // longitude

这是实际数据库布局的图片

我不知道"g" 代表什么，但我认为"l" 代表位置，因为它是CLLocation 类型，正如.observe(.keyEntered, with: { (key: String!, location: CLLocation!) 的参数中所述。

在数据库内部，0 键和 1 被保存为 snapshot.value 数组 CLLocationDegrees 或 Double。

要获得latitude 和longitude，我使用了let arr = snapshot.value as? [CLLocationDegrees]，但let arr = snapshot.value as? [Double] 也有效。

创建一个 ref，其子名称与您的 geoLocations ref 的名称相同 > 然后添加 userId 的子 > 然后为位置子添加“l”的子。

运行observeSingleEvent(of: .value 并在回调中将snapshot.value 作为[CLLocationDegrees] 的数组运行

// *** if using CLLocationDegrees be to import CoreLocation ***
import CoreLocation

let geoLocationsRef = Database.database().reference()
                        .child("geoLocations") // name of my geoRef in Firebase
                        .child("abc123xyz456") // the userId I'm observing
                        .child("l") // the "l" is the child to observe

geoLocationsRef.observeSingleEvent(of: .value, with: { (snapshot) in

    if !snapshot.exists() { return }

    guard let arr = snapshot.value as? [CLLocationDegrees] else { return }

    if arr.count > 1 {

        let latitude = arr[0]
        print(latitude)

        let longitude = arr[1]
        print(longitude)

        // do whatever with the latitude and longitude
    }
})

这是我使用 dispatchGroup() 的问题的答案：

func queryLocationOfSubsetOfUsersInRadius() {

    let dispatchGroup = DispatchGroup()

    for user in subsetOfUsersInRadius {

        dispatchGroup.enter()

        let userId = user.userId

        let geoLocationsRef = Database.database().reference()
            .child("geoLocations")
            .child(userId)
            .child("l")

        geoLocationsRef.observeSingleEvent(of: .value, with: { (snapshot) in

            // this user may have deleted their location
            if !snapshot.exists() {
                dispatchGroup.leave()
                return
            }

            guard let arr = snapshot.value as? [CLLocationDegrees] else {
                dispatchGroup.leave()
                return
            }

            if arr.count > 1 {

                let latitude = arr[0]
                print(latitude)

                let longitude = arr[1]
                print(longitude)

                // do whatever with the latitude and longitude
            }

            dispatchGroup.leave()
        })
    }

    dispatchGroup.notify(queue: .global(qos: .background)) {

        // now animate the annotation from the user's inital old location (if they moved) on the mapView to their new location on the mapView. It's supposed to look like Uber's cars moving. Happens on main thread
    }
}