場所更新時に以前のマーカーを削除します

Question

マップ上にマーカーを配置しました。マーカーの位置が変わると、地図上に別のマーカーが置かれますが、最後のマーカーはそのままにして、同じIDの複数のマーカーをマップ上に作成します。

私は場所の更新として以前のマーカーをクリアする方法はありません。

firebaseデータベースから任意の配列の場所の変更を取得しています。ここで

は私のコードです：

import android.content.Intent; 
import android.media.MediaPlayer; 
import android.net.Uri; 
import android.os.Bundle; 
import android.os.Handler; 
import android.support.design.widget.NavigationView; 
import android.support.design.widget.Snackbar; 
import android.support.v4.view.GravityCompat; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.ActionBarDrawerToggle; 
import android.support.v7.widget.Toolbar; 
import android.telephony.SmsManager; 
import android.util.Log; 
import android.view.MenuItem; 
import android.view.View; 

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 com.google.firebase.database.DataSnapshot; 
import com.google.firebase.database.DatabaseError; 
import com.google.firebase.database.DatabaseReference; 
import com.google.firebase.database.FirebaseDatabase; 
import com.google.firebase.database.ValueEventListener; 

import java.util.ArrayList; 
import java.util.Map; 

public class MapsActivity extends MainActivity implements OnMapReadyCallback { 
// flag for Internet connection status 
Boolean isInternetPresent = false; 

// Connection detector class 
ConnectionDetector cd; 

// Alert Dialog Manager 
AlertDialogManager alert = new AlertDialogManager(); 

// GPS Location 
GPSTracker gps; 

Handler handler = new Handler(); 
Runnable refresh; 


final int[] count = {0}; 

final ArrayList<String> locationData = new ArrayList<>(); 
final ArrayList<String> DriverInfo = new ArrayList<>(); 

public GoogleMap mMap; 
public Marker marker; 

MediaPlayer mediaPlayer; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_maps); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
      this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
    drawer.setDrawerListener(toggle); 
    toggle.syncState(); 

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view); 
    navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() { 
     @Override 
     public boolean onNavigationItemSelected(MenuItem item) { 
      int id = item.getItemId(); 

      if (id == R.id.profile) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, ProfileActivity.class)); 
      } else if (id == R.id.nearby) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, NearbyActivity.class)); 
      } else if (id == R.id.notification) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, NotificationActivity.class)); 
      } else if (id == R.id.setting) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, SettingsActivity.class)); 
      } else if (id == R.id.faq) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, FaqActivity.class)); 
      } else if (id == R.id.emergecy_contact) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, EmergencyContactActivity.class)); 
      } else if (id == R.id.support) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, SupportActivity.class)); 
      } else if (id == R.id.help) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, HelpActivity.class)); 
      } else if (id == R.id.about_us) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, AboutUsActivity.class)); 
      } else if (id == R.id.rate) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, RateUsActivity.class)); 
      } else if (id == R.id.share) { 
       finish(); 
       startActivity(new Intent(MapsActivity.this, ShareActivity.class)); 
      } 

      DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
      drawer.closeDrawer(GravityCompat.START); 
      return true; 
     } 
    }); 

    mediaPlayer = MediaPlayer.create(this, R.raw.demonstrative); 

    cd = new ConnectionDetector(getApplicationContext()); 

    // Check if Internet present 
    isInternetPresent = cd.isConnectingToInternet(); 
    if (!isInternetPresent) { 
     // Internet Connection is not present 
     alert.showAlertDialog(MapsActivity.this, "Internet Connection Error", 
       "Please connect to working Internet connection", false); 
     // stop executing code by return 
     return; 
    } 

    // creating GPS Class object 
    gps = new GPSTracker(this); 

    // check if GPS location can get 
    if (gps.canGetLocation()) { 
     Log.d("Your Location", "latitude:" + gps.getLatitude() + ", longitude: " + gps.getLongitude()); 
    } else { 
     // Can't get user's current location 
     alert.showAlertDialog(MapsActivity.this, "GPS Status", 
       "Couldn't get location information. Please enable GPS", 
       false); 
     // stop executing code by return 
     return; 
    } 
    // Obtain the SupportMapFragment and get notified when the map is ready to be used. 
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager() 
      .findFragmentById(R.id.map); 
    mapFragment.getMapAsync(this); 


    //Retrive data from firebase 

    final FirebaseDatabase database = FirebaseDatabase.getInstance(); 
    final DatabaseReference myRef = database.getReference().child("users"); 


    myRef.addValueEventListener(new ValueEventListener() { 
     @Override 
     public void onDataChange(DataSnapshot dataSnapshot) { 
      collectLocation((Map<String, Object>) dataSnapshot.getValue()); 
      collectdriverInfo((Map<String, Object>) dataSnapshot.getValue()); 
     } 

     @Override 
     public void onCancelled(DatabaseError databaseError) { 

     } 

    }); 
} 


//Retrieve location from database 
public void collectLocation(Map<String, Object> users) { 
    for (Map.Entry<String, Object> entry : users.entrySet()) { 
     //Get user map 
     Map singleUser = (Map) entry.getValue(); 
     //Get phone field and append to list 
     locationData.add((String) singleUser.get("location")); 

     count[0]++; 

    } 

    System.out.println("Location: " + locationData.toString()); 
    System.out.println("My count is: " + count[0]); 
} 

//Retrive driver info from database 
public void collectdriverInfo(Map<String, Object> users) { 
    final String[] userName = new String[count[0]]; 
    final String[] userContact = new String[count[0]]; 

    final double[] latitude = new double[count[0]]; 
    final double[] longitude = new double[count[0]]; 


    for (Map.Entry<String, Object> entry : users.entrySet()) { 
     //Get user map 
     Map singleUser = (Map) entry.getValue(); 
     //Get phone field and append to list 
     DriverInfo.add((String) singleUser.get("driverInfo")); 
    } 
    System.out.println("Driver Information: " + DriverInfo.toString()); 


    //Convert location string to double 
    int j = 0; 
    for (String loc : locationData) { 
     System.out.println("LocationMMdm" + loc); 
     String[] Location = loc.split(","); 
     latitude[j] = Double.parseDouble(Location[0]); 
     longitude[j] = Double.parseDouble(Location[1]); 
     System.out.println("lat: " + latitude[0] + " " + "log: " + longitude[0]); 

     j++; 
    } 

    //Split driver info and add marker on map 
    int i = 0; 
    for (String data : DriverInfo) { 
     System.out.println("datainfo " + data); 
     String[] singleEntry = data.split(","); 
     userName[i] = singleEntry[0]; 
     userContact[i] = singleEntry[1]; 

     mMap.addMarker(new MarkerOptions().position(new LatLng(latitude[i], longitude[i])). 
        title(userName[i]). 
        snippet(userContact[i]). 
        flat(true). 
        alpha(0.9f). 
        anchor(0.5f, 0.5f). 
        rotation((0.0f)). 
        icon(BitmapDescriptorFactory.fromResource(R.drawable.markeramb))); 
      i++; 
    } 


    mMap.setOnInfoWindowLongClickListener(new GoogleMap.OnInfoWindowLongClickListener() { 
     @Override 
     public void onInfoWindowLongClick(Marker marker) { 
      String phoneno = marker.getSnippet(); 
      double myLat = gps.getLatitude(); 
      double myLog = gps.getLongitude(); 
      String title = marker.getTitle(); 
      String msg = myLat + ", " + myLog; 

      try { 
       SmsManager smsManager = SmsManager.getDefault(); 
       smsManager.sendTextMessage(phoneno, null, msg, null, null); 

       View view = findViewById(android.R.id.content); 
       Snackbar.make(view, "Message Sent", Snackbar.LENGTH_LONG).show(); 

       mediaPlayer.start(); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 

    //Call to the ambulance driver 
    mMap.setOnInfoWindowClickListener(new GoogleMap.OnInfoWindowClickListener() { 
     @Override 
     public void onInfoWindowClick(Marker marker) { 
      try { 
       String uri = "tel:" + marker.getSnippet(); 
       if (marker.getSnippet() == null) { 
        alert.showAlertDialog(MapsActivity.this, "Not Present", 
          "Contact no. not available", false); 
       } else { 
        finish(); 
        Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(uri)); 
        startActivity(callIntent); 
       } 

      } catch (Exception e) { 
       e.printStackTrace(); 
      } 

     } 
    }); 
    System.out.println("Users name are: " + userName.toString()); 
    System.out.println("Users count is: " + userContact.toString()); 
    System.out.println("Count is:" + count[0]); 
} 



@Override 
public void onMapReady(GoogleMap googleMap) { 
    mMap = googleMap; 
    mMap.setMyLocationEnabled(true); 
    double myLatitude = gps.getLatitude(); 
    double myLongitude = gps.getLongitude(); 
    LatLng latLng = new LatLng(myLatitude, myLongitude); 
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 10)); 
} 


@Override 
public void onBackPressed() { 
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    if (drawer.isDrawerOpen(GravityCompat.START)) { 
     drawer.closeDrawer(GravityCompat.START); 
    } else { 
     super.onBackPressed(); 
     finish(); 
     startActivity(new Intent(MapsActivity.this, MainActivity.class)); 
    } 
    } 
} 

Answer 1

以下だけValueEventListenerのOnDataChangeの方法の最初の行としてmMap.clear（）を使用したマーカー

if (destnationMarker != null) { 

    destnationMarker.remove(); 
    mMap.clear(); 
    destnationMarker = null; 

}