ios - swift 函数返回值未正确返回

Question

   func getLatsAndLongs() -> (LATITUDE: Double, LONGITUDE: Double, DESIREDLAT: Double, DESIREDLONG: Double) {



    self.forwardGeocoding("\(addressTxtFld.text) \(cityTxtFld.text), \(stateTxtFld.text)", completion: {
        success, coordinate in

        if success {
            self.lat = coordinate.latitude
            self.long = coordinate.longitude

            print("\(self.lat) is the latitude for the initial location")
            print("\(self.long) is the longitude for the initial location")

            self.INITIAL_DESTINATION_LATITUDE = self.lat
            self.INITIAL_DESTINATION_LONGITUDE = self.long

            var initialLocation = CLLocationCoordinate2DMake(self.INITIAL_DESTINATION_LATITUDE, self.INITIAL_DESTINATION_LONGITUDE)



        } else {
            print("Error at forwardGeocoding @willcohen @ERRORALERT")
        }
    })


    self.forwardGeocodingDesired("\(addressTxtFldDest.text) \(cityTxtFldDest.text), \(stateTxtFldDest.text)", completion: {
        success, coordinate in

        if success {
            self.desiredLat = coordinate.latitude
            self.desiredLong = coordinate.longitude

            print("\(self.desiredLat) is the latitude for the desired location")
            print("\(self.desiredLong) is the longitude for the desired locaiton")

            self.DESIRED_DESTIANTION_LATITUDE = self.desiredLat
            self.DESIRED_DESTINATION_LONGITUDE = self.desiredLong

            var desiredLocation = CLLocationCoordinate2DMake(self.DESIRED_DESTIANTION_LATITUDE, self.DESIRED_DESTINATION_LONGITUDE)




        } else {
            print("Error at forwardGeocodingDesired @willcohen @ERRORALERT")
        }

    })

    return (lat,long,desiredLat,desiredLong)

}


           let latsAndLongs = getLatsAndLongs()

        let latFF = latsAndLongs.LATITUDE
        let longFF = latsAndLongs.LONGITUDE
        let latDFF = latsAndLongs.DESIREDLAT
        let longDFF = latsAndLongs.DESIREDLONG

        print("\(latFF) final lat")
        print("\(longFF) final long")
        print("\(latDFF) final latD")
        print("\(longDFF) final longD")

好的。因此，当我尝试打印最后 4 行中的所有行时，每次都显示为“0”。请注意，两条地理编码线 (self.forwardGeocoding) & (self.forwardGeocodingDesired) 不是问题，它们工作正常，但我不知道为什么它们不打印正确的 Double 值。如有任何建议，我们将不胜感激，谢谢。

Answer 1

forwardGeocoding 和 forwardGeocodingDesired 通过网络调用需要时间执行的操作。这是使用后台线程完成的，以免阻塞 UI。当操作完成时，将执行完成闭包中的代码。

您的 getLatsAndLongs 函数返回 lat、long、desiredLat 和 desiredLong 之前操作已经完成，因此在您的闭包设置这些变量之前。

您可以将完成处理程序传递给 getLatsAndLongs 以在操作完成后调用，但您的情况很复杂，因为您并行执行两个地理编码操作，并且您不知道哪个会先完成。您可以从第一个的完成处理程序中分派(dispatch)第二个，但这会更慢。更好的方法是使用 dispatch_group:

func getLatsAndLongs(completion:(initialLocation: CLLocationCoordinate2D?, desiredLocation: CLLocationCoordinate2D?)->Void)  {

    let dispatchGroup = dispatch_group_create()

    var initialLocation: CLLocationCoordinate2D?
    var desiredLocation: CLLocationCoordinate2D?

    dispatch_group_enter(dispatchGroup)

    self.forwardGeocoding("\(addressTxtFld.text) \(cityTxtFld.text), \(stateTxtFld.text)", completion: {
        success, coordinate in
        if success {
            initialLocation = coordinate
        } else {
            print("Error at forwardGeocoding @willcohen @ERRORALERT")
        }
        dispatch_group_leave(dispatchGroup)
    })


    self.forwardGeocodingDesired("\(addressTxtFldDest.text) \(cityTxtFldDest.text), \(stateTxtFldDest.text)", completion: {
        success, coordinate in

        if success {
            desiredLocation = coordinate
        } else {
            print("Error at forwardGeocodingDesired @willcohen @ERRORALERT")
        }
        dispatch_group_leave(dispatchGroup)
    })

    dispatch_group_notify(dispatchGroup, dispatch_get_main_queue()) {
        completion(initialLocation:initialLocation,desiredLocation:desiredLocation)
    }
}

用法:

getLatsAndLongs { (initialLocation, desiredLocation) in
    print(initialLocation)
    print(desiredLocation)
}