How to only show post within one mile in Flutter

Question

I am trying to make a functionality that can show nearby posts from the user.

From my code, first I am reading data from the firebase (timelineLocalRef), such that

getTimelineLocal() async {
QuerySnapshot snapshotLocal = await timelineLocalRef
    .doc('test')
    .collection('userPosts')
    .orderBy('timestamp', descending: true)
    .get();

List<PostL> postsLocal =
    snapshotLocal.docs.map((doc) => PostL.fromDocument(doc)).toList();
setState(() {
  this.postsLocal = postsLocal;
});

In timelineRef, information for posts are saved such that,

Once I have obtained the post information, I am also taking the user location using the Geolocator.

  getUserLocation() async {
    Position position = await Geolocator()
        .getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
    posXuser = position.latitude;
    posYuser = position.longitude;
  }

With the user location (posXuser, posYuser) and the posting location (posX,posY), I should be able to calculate the distance between two using the function below.

  double calculateDistance(lat1, lon1, lat2, lon2) {
    var p = 0.017453292519943295;
    var c = cos;
    var a = 0.5 -
        c((lat2 - lat1) * p) / 2 +
        c(lat1 * p) * c(lat2 * p) * (1 - c((lon2 - lon1) * p)) / 2;
    return 0.621371 * 12742 * asin(sqrt(a));
    //return mile distance
  }

So What I want is from the first code, when I make postsLocal, I want to only import the post within 1 mile away. Can you help me with how to make a conditional mapping snapshots?

Solution

There are multiple way of doing the same depends on requirements:

1. Get a Current Latitude and Longitude

2. Create a api that returns destination Postlist along with their PostTimelatitude and a PostTimelatitude in it.

3. find a difference between them using a below code snippet.

   double distanceInMeters = Geolocator.distanceBetween(
       currentLatitudeTxt,
       currentLongitudeTxt,
       double.parse(posttimeLatitude),
       double.parse(posttimeLatitude),
     );      
   

4. Convert a distance in Meters to mile and use a listview Widget.

For your reference consider a code snippet below:

  _handleAllRestaurantListResponse(value) {
var arrData = value
    .map<RestaurantModel>((json) => RestaurantModel.fromJson(json))
    .toList();
arrayRestaurantList = arrData;
print("ALL RESTAURANT LENGTH : ${arrayRestaurantList.length}");

if (arrayRestaurantList.isNotEmpty) {
  for (var item in arrayRestaurantList) {
    var responseLatitude = item.latitude;
    var responseLongitude = item.longitude;
    print(responseLatitude);
    print(responseLongitude);
    if (responseLatitude != null && responseLongitude != null) {
      double distanceInMeters = Geolocator.distanceBetween(
        currentLatitudeTxt,
        currentLongitudeTxt,
        double.parse(responseLatitude),
        double.parse(responseLongitude),
      );
      double distanceInKm = distanceInMeters / 1000;
      int roundedDistanceInKM = distanceInKm.toInt();
      if (nearByRestaurantRadius > roundedDistanceInKM) {
        filterRestaurantList.add(item);
      }
    }
  }
} else {
  print("object");
}

}