無法使用Firebase更新Google地圖位置

Question

我正嘗試將位置表單Firebase數據庫更新爲我的Android應用程序中的Google地圖。我已經使用firebase的onDataChange方法來實現這一點。我的問題是，即使Firebase數據庫中的高度和經度位置已更改，我仍無法更新Google地圖上的位置。以下是我的MapsActivity.java類的代碼。

import android.support.v4.app.FragmentActivity; 
import android.os.Bundle; 
import android.util.Log; 

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.LatLng; 
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; 

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback { 

    private GoogleMap mMap; 
    String value; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_maps); 
     // 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); 

     FirebaseDatabase database = FirebaseDatabase.getInstance(); 
     DatabaseReference myRef = database.getReference("Location"); 

     // myRef.setValue("Hello, World!"); 

     myRef.addValueEventListener(new ValueEventListener() { 
      @Override 
      public void onDataChange(DataSnapshot dataSnapshot) { 
       value = dataSnapshot.getValue(String.class); 
       String [] separated = value.split(","); 
       String latiPos= separated[0].trim(); 
       String longiPos =separated[1].trim(); 
       String TAG ="VAL"; 
       double dLat = Double.parseDouble(latiPos); 
       double dLong = Double.parseDouble(longiPos); 
       // Add a marker in Sydney and move the camera 
       LatLng sydney = new LatLng(dLat, dLong); 
       mMap.addMarker(new MarkerOptions().position(sydney).title(latiPos+" "+longiPos)); 


      } 

      @Override 
      public void onCancelled(DatabaseError databaseError) { 

      } 
     }); 
    } 


    /** 
    * Manipulates the map once available. 
    * This callback is triggered when the map is ready to be used. 
    * This is where we can add markers or lines, add listeners or move the camera. In this case, 
    * we just add a marker near Sydney, Australia. 
    * If Google Play services is not installed on the device, the user will be prompted to install 
    * it inside the SupportMapFragment. This method will only be triggered once the user has 
    * installed Google Play services and returned to the app. 
    */ 
    @Override 
    public void onMapReady(GoogleMap googleMap) { 
     mMap = googleMap; 

     // Add a marker in Sydney and move the camera 
    // LatLng sydney = new LatLng(-34, 151); 
     // mMap.addMarker(new MarkerOptions().position(sydney).title(value)); 
     //mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney)); 
    } 
} 

Answer 1

有兩件事情我會建議，以解決您的問題：

1. 裹存儲在FirebaseDatabase在一個Java對象可以輕鬆地存儲和檢索數據的數據。現在，您正在做大量工作來處理您存儲在數據庫中的數據。因此， 定義了一個類，它表示要作爲Java對象存儲的數據。然後你的讀取/寫入 到數據庫將會更容易。以下是您可以用來代表地圖標記 的類的示例，其基礎是我在上面的代碼中看到的。您可以對其進行定製以滿足您的需求：

   public class LocationMarker { 
   
       double latitude; 
       double longitude; 
   
   
       /** 
       * Required Empty Constructor used by Firebase 
       */ 
       public LocationMarker() { 
       } 
   
       public LocationMarker(double latitude, double longitude) { 
        this.latitude = latitude; 
        this.longitude = longitude; 
   
       } 
   
       public double getLatitude() { 
        return latitude; 
       } 
   
       public void setLatitude(double latitude) { 
        this.latitude = latitude; 
       } 
   
       public double getLongitude() { 
        return longitude; 
       } 
   
       public void setLongitude(double longitude) { 
        this.longitude = longitude; 
       } 
   
   
       /** 
       * These getters will be ignored when the object is serialized into a JSON object. 
       * Since they will be ignored this means that they don't need a corresponding property (field) 
       * in the Database. This is how we can return a value without having them declared as an instance variable. 
       */ 
   
       @Exclude 
       public LatLng getPosition(){ 
        return new LatLng(latitude, longitude); 
       } 
   
       @Exclude 
       public String getTitle(){ 
        return Double.toString(latitude) + " " + Double.toString(longitude); 
       } 
   } 
   

   現在您可以更輕鬆地將數據寫入數據庫。

   DatabaseReference myRef = FirebaseDatabase.getInstance().getReference(); 
   double latitude = -34; 
   double longitude = 151; 
   LocationMarker locationMarker = new LocationMarker(latitude,longitude); 
   myRef.child("Location").setValue(locationMarker); 
   

   和閱讀：

   myRef.addValueEventListener(new ValueEventListener() { 
       @Override 
       public void onDataChange(DataSnapshot dataSnapshot) { 
   
        LocationMarker locationMarker = dataSnapshot.getValue(LocationMarker.class); 
   
        if(locationMarker != null){ 
         LatLng sydney = locationMarker.getPosition(); 
         mMap.addMarker(new MarkerOptions() 
               .position(sydney) 
               .title(locationMarker.getTitle)); 
        } 
       } 
   
       @Override 
       public void onCancelled(DatabaseError databaseError) { 
   
       } 
   }); 
   

2. 的呼叫onMapReady()和onDataChange()同步發生。 這意味着你的挑戰是你無法控制onMapReady（）被調用的時間。 當您的ValueEventListener調用onDataChange()時，您也無法控制。 正如現在寫的，在您有一個有效的GoogleMap對象之前，您的FirebaseDatabase調用可能會返回。所以在通話添加ValueEventListener到onMapReady()：

   @Override 
   public void onMapReady(GoogleMap googleMap) { 
       mMap = googleMap; 
       addValueEventListener(); 
   } 
   
   //.... 
   
   private void addValueEventListener(){ 
   
       if(mMap == null) return; 
   
       myRef.addValueEventListener(new ValueEventListener() { 
         @Override 
         public void onDataChange(DataSnapshot dataSnapshot) { 
   
          LocationMarker locationMarker = dataSnapshot.getValue(LocationMarker.class); 
   
          if(locationMarker != null){ 
          LatLng sydney = locationMarker.getPosition(); 
          mMap.addMarker(new MarkerOptions() 
               .position(sydney) 
               .title(locationMarker.getTitle)); 
          } 
         } 
   
         @Override 
         public void onCancelled(DatabaseError databaseError) { 
   
         } 
       }); 
   } 
   

希望這有助於顯示存儲和檢索地圖標記到您的數據庫。這應該在「位置」下存儲一個標記。您必須對多個標記的數據庫結構進行調整。此外，請務必刪除所有添加的聽衆:)