如何找到离用户最近的标记?

Question

我对 android 开发很陌生，我想知道我是否可以找到离用户最近的标记，并知道哪个标记最接近使用折线和谷歌方向 API 将用户引导到那里。标记的位置取自一个数据库，我已经将其解析为一个列表数组，然后我使用该数组在地图上放置标记。我试图从其他问题中寻求帮助，但它们似乎不适合我的项目。

如果我可以找到离用户最近的标记，如果没有，我该怎么做，我可以使用另一种方法？

这是我的主要活动代码：

package com.example.defiblocator;
import android.Manifest;
import android.content.pm.PackageManager;
import android.location.Location;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class MainActivity extends AppCompatActivity implements OnMapReadyCallback,
LocationListener,GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener{
public static TextView data;
public static String location;
GoogleMap mapAPI;
SupportMapFragment mapFragment;
Location mLastLocation;
Marker mCurrLocationMarker;
GoogleApiClient mGoogleApiClient;
LocationRequest mLocationRequest;
String delimiter = ",";
List<String> full = new ArrayList<>();
List<String> size = new ArrayList<>();
private ArrayList<LatLng> markerCoords = new ArrayList<LatLng>();
String info;
String name;
Double lat;
Double lng;
Button emergency;
LatLng mark;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.mapAPI);
mapFragment.getMapAsync(this);
data = findViewById(R.id.fetchdata);
new fetchData(new CallbackClass()).execute();
emergency = findViewById(R.id.button);
emergency.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
}
});
}

@Override
public void onMapReady(GoogleMap googleMap) {
mapAPI = googleMap;
mapAPI.getUiSettings().setZoomControlsEnabled(true);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
mapAPI.setMyLocationEnabled(true);
//mapAPI.setOnMyLocationChangeListener(this);
}
} else {
buildGoogleApiClient();
mapAPI.setMyLocationEnabled(true);
}
}
protected synchronized void buildGoogleApiClient() {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API).build();
mGoogleApiClient.connect();
}
@Override
public void onConnected(Bundle bundle) {
mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(1000);
mLocationRequest.setFastestInterval(1000);
mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
}
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onLocationChanged(Location location) {
/*mLastLocation = location;
if (mCurrLocationMarker != null) {
mCurrLocationMarker.remove();
}*/
//Place current location marker
LatLng patient = new LatLng(location.getLatitude(), location.getLongitude());
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(patient);
markerOptions.title("Patient");
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE));
mCurrLocationMarker = mapAPI.addMarker(markerOptions);
//move map camera
mapAPI.animateCamera(CameraUpdateFactory.zoomTo(11));
mapAPI.moveCamera(CameraUpdateFactory.newLatLng(patient));
//stop location updates
if (mGoogleApiClient != null) {
LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
}
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
public class CallbackClass implements CallbackInterface {
@Override
public void onSuccess(String callbackData) {
info = callbackData;
full = Arrays.asList(info.split(delimiter));
size = Arrays.asList(info.split(delimiter));
Integer x = 0;
while(x != size.size()){
name = full.get(x);
x += 1;
lat = Double.valueOf(full.get(x));
x += 1;
lng = Double.valueOf(full.get(x));
x += 1;
LatLng pos = new LatLng(lat, lng);
mapAPI.addMarker(new MarkerOptions().position(pos).title(name));
mark = new LatLng(lat,lng);
markerCoords.add(mark);
}
}
@Override
public void onFailure() {
}
}
}

这是从数据库中解析 JSON 的代码，任何帮助将不胜感激。

package com.example.defiblocator;
import android.app.Application;
import android.os.AsyncTask;
import android.widget.TextView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class fetchData extends AsyncTask <Void,Void,Void>{
CallbackInterface callbackInterface;
String data = "";
String json_url;
String singleParsed = "";
public String dataParsed = "";
String sent;
public fetchData(CallbackInterface callbackInterface) {
this.callbackInterface = callbackInterface;
}

public Integer x = 0;
@Override
protected void onPreExecute(){
json_url = "http://defiblocator.ml/json_get_data.php";
dataParsed = "";
}
@Override
protected Void doInBackground(Void... voids) {

try {
URL url = new URL(json_url);
HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line = "";
while(line != null){
line = bufferedReader.readLine();
data = data + line;
}
JSONArray JA = new JSONArray(data);
for(int i =0 ; i <JA.length(); i++){
JSONObject JO = (JSONObject) JA.get(i);
singleParsed = JO.get("name") + "," + JO.get("lat") + "," +JO.get("lng") + "," ;
dataParsed = dataParsed + singleParsed ;
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException | JSONException e){
e.printStackTrace();
}
return null;
}

@Override
protected void onPostExecute(Void aVoid) {
MainActivity.data.setText(dataParsed);
callbackInterface.onSuccess(dataParsed);
}

}

Answer 1

您可以使用一个简单的距离公式来存档以下内容：

private Double distance(Double lat1, Double lon1, Double lat2, Double lon2) {
return Math.sqrt (Math.pow((lat1 - lat2), 2) - Math.pow((lon1 - lon2), 2));
}

// The user Location
currentLat = xxxx;
currentLon = xxxx;
if ((markerCoords != null) && (markerCoords.size() > 0)) {
LatLng near = markerCoords.get(0);
for (int x = 1; x < markerCoords.size(); x++) {
Double lat = markerCoords.get(x).latitude;
Double lon = markerCoords.get(x).longitude;
Double currentMarkerdistance = distance(
currentLat, 
currentLon, 
markerCoords.get(x).latitude,
markerCoords.get(x).longitude);
Double nearMarkerdistance = distance(
currentLat, 
currentLon, 
near.latitude,
near.longitude);
if (currentMarkerdistance < nearMarkerdistance) {
near = markerCoords.get(x);
}
}
}
// After this process the near variable will hold the near marker