How retrieve coordinates in same order? - swift

Question

"-KHbCuQflKHrJiUmfpG0" : {
"coordinates" : {
"-KHbCuQflKHrJiUmfpG1" : {
"latitude" : 13.17078652595298,
"longitude" : -59.5775944578738
},
"-KHbCuQflKHrJiUmfpG2" : {
"latitude" : 13.15541190861343,
"longitude" : -59.57619643155932
},
"-KHbCuQg9W_tebl1pU66" : {
"latitude" : 13.148444967591,
"longitude" : -59.5589266947333
}
},
"subtitle" : "patrick",
"title" : "River",
"type" : "polyline"
},
This is my JSON structure for saving polylines and I need retrieve coordinates in same order.
This is my code for obtaining coordinates and creating polylines.
// geoobject.key - is ID of geoobject (for loop geoobjects) "-KHbCuQflKHrJiUmfpG0"
DataService.dataService.getGeoObject(geoobject.key).observeEventType(.Value, withBlock: { geoSnapshot in
var coordinatesPolyline = [CLLocationCoordinate2D]()
if let geoDictionary = geoSnapshot.value as? Dictionary<String, AnyObject> {
let id = geoSnapshot.key
if geoDictionary["type"] as! String == "polyline" {
if let coords = geoDictionary["coordinates"] as? [String:[String:Double]] {
let contents = coords.values
for content in contents {
let latitude = content["latitude"]
let longitude = content["longitude"]
let point = CLLocationCoordinate2D(latitude: latitude!, longitude: longitude!)
coordinatesPolyline.append(point)
}
// coordintesPolyline contains shuffle coordinates
let polyline = Polyline(coordinates: &coordinatesPolyline, count: coordinatesPolyline.count)
//coordinates = []
polyline.id = geoSnapshot.key
polyline.title = geoDictionary["title"] as? String
polyline.subtitle = geoDictionary["subtitle"] as? String
self.polylines.insert(polyline, atIndex: 0)
}
}
})
I rendered polylines but polylines are renderder bad because coordinates are shuffle.
Does anyone know how to get coordinates in the correct order. Firebase retrieve coordinates shuffle and then rendering doesn't work well.
Thank you for some advice.

Answer 1

When reading firebase data by .Value, ALL of the data within the node is returned in the snapshot.
If you want the data in a specific order, you need to decide what 'thing' you want it ordered by. The natural order is by key, but if you want it ordered by some other parameter, you need to include that in you firebase structure, and then add orderedBy to your observe.
One you have the data by .Value, you then need to iterate over each child within the snapshot to access that nodes data. For example
If your Firbase structure is
"coordinates" : {
"-KHbCuQflKHrJiUmfpG1" : {
"latitude" : 13.17078652595298,
"longitude" : -59.5775944578738
},
"-KHbCuQflKHrJiUmfpG2" : {
"latitude" : 13.15541190861343,
"longitude" : -59.57619643155932
},
"-KHbCuQg9W_tebl1pU66" : {
"latitude" : 13.148444967591,
"longitude" : -59.5589266947333
}
Then the snapshot contains All of that data. Iterate over the snapshot and work with each child:
ref.observeEventType(.Value, withBlock: { geoSnapshot in
for child in geoSnapshot.children {
let lat = child["latitude"] as? String
let long = child["longitude"] as? String
print("lat = \(lat) long = \(long)"
}
})
(didn't test that code but it's close)
Oh, and one other thing. ObserveEventOfType(.Value) will continually observe the node for changes - add, change or remove and will fire any time one of those events occur.
If you just want a one-shot, use ObserveSingleEventOfType(.Value)