當我讀取GPS位置時，Android返回null

Question

我想使用此代碼讀取我的Android設備的位置，但它在經度和緯度上返回null，但我添加了正確的權限，並且在Android設備上嘗試了它， GPS已啓用。我試圖找出問題，發現這if語句是不正確的

if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 

，我試圖改變！=到==它也沒工作，如果我試圖如果刪除這個聲明中，它給我的錯誤： 呼叫需要可以由用戶被拒絕權限：代碼應明確檢查，看是否許可可用（與checkPermission）或明確處理潛在SecurityException 這是我的GPS代碼：

public class GPSPosition extends Service implements LocationListener { 
    private final Context mContext; 

    // flag for GPS status 
    boolean isGPSEnabled = false; 

    // flag for network status 
    boolean isNetworkEnabled = false; 

    // flag for GPS status 
    boolean canGetLocation = false; 

    Location location; // location 
    double latitude; // latitude 
    double longitude; // longitude 

    // The minimum distance to change Updates in meters 
    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters 

    // The minimum time between updates in milliseconds 
    private static final long MIN_TIME_BW_UPDATES = 100 * 60*1; // 60 seconds 

    // Declaring a Location Manager 
    protected LocationManager locationManager; 

    public GPSPosition(Context context) { 
     this.mContext = context; 
     getLocation(); 
    } 

    public Location getLocation() { 
     try { 
      locationManager = (LocationManager) mContext 
        .getSystemService(LOCATION_SERVICE); 

      // getting GPS status 
      isGPSEnabled = locationManager 
        .isProviderEnabled(LocationManager.GPS_PROVIDER); 

      // getting network status 
      isNetworkEnabled = locationManager 
        .isProviderEnabled(LocationManager.NETWORK_PROVIDER); 

      if (!isGPSEnabled && !isNetworkEnabled) { 
       // no network provider is enabled 
      } else { 
       this.canGetLocation = true; 
       // First get location from Network Provider 
       if (isNetworkEnabled) { 

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 
         Log.d("enabless1", "Network"); 
         locationManager.requestLocationUpdates(
           LocationManager.NETWORK_PROVIDER, 
           MIN_TIME_BW_UPDATES, 
           MIN_DISTANCE_CHANGE_FOR_UPDATES, this); 
         Log.d("Network", "Network"); 
         if (locationManager != null) { 
          location = locationManager 
            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER); 
          if (location != null) { 
           latitude = location.getLatitude(); 
           longitude = location.getLongitude(); 
          } 
         } 
        } 
       } 
       // if GPS Enabled get lat/long using GPS Services 
       if (isGPSEnabled) { 
        if (location == null) { 
         locationManager.requestLocationUpdates(
           LocationManager.GPS_PROVIDER, 
           MIN_TIME_BW_UPDATES, 
           MIN_DISTANCE_CHANGE_FOR_UPDATES, this); 
         Log.d("GPS Enabled", "GPS Enabled"); 
         if (locationManager != null) { 
          location = locationManager 
            .getLastKnownLocation(LocationManager.GPS_PROVIDER); 
          if (location != null) { 
           latitude = location.getLatitude(); 
           longitude = location.getLongitude(); 
          } 
         } 
        } 
       } 
      } 

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

     return location; 
    } 
    public double getLatitude(){ 
     if(location != null){ 
      latitude = location.getLatitude(); 
     } 

     // return latitude 
     return latitude; 
    } 

    /** 
    * Function to get longitude 
    * */ 
    public double getLongitude(){ 
     if(location != null){ 
      longitude = location.getLongitude(); 
     } 

     // return longitude 
     return longitude; 
    } 
    public boolean canGetLocation() { 
     return this.canGetLocation; 
    } 

    /** 
    * Function to show settings alert dialog 
    * */ 
    public void showSettingsAlert(){ 
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext); 

     // Setting Dialog Title 
     alertDialog.setTitle("GPS is settings"); 

     // Setting Dialog Message 
     alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?"); 

     // Setting Icon to Dialog 
     //alertDialog.setIcon(R.drawable.delete); 

     // On pressing Settings button 
     alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog,int which) { 
       Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS); 
       mContext.startActivity(intent); 
      } 
     }); 

     // on pressing cancel button 
     alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int which) { 
       dialog.cancel(); 
      } 
     }); 

     // Showing Alert Message 
     alertDialog.show(); 
    } 




    public void onLocationChanged(Location location) { 

     // Toast.makeText(mContext, "log:" + Double.toString(location.getLongitude()) + ", lat: " + Double.toString(location.getLatitude()), Toast.LENGTH_LONG).show(); 
    } 

    @Override 
    public void onProviderDisabled(String provider) { 
    } 

    @Override 
    public void onProviderEnabled(String provider) { 
    } 

    @Override 
    public void onStatusChanged(String provider, int status, Bundle extras) { 
    } 

    @Nullable 
    @Override 
    public IBinder onBind(Intent intent) { 
     return null; 
    } 
} 

這裏我稱它們爲MainActivity：

public class MainActivity extends AppCompatActivity { 

    public static String lat="10"; 
    public static String lang="10"; 
    GPSPosition gps; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

//  Toast.makeText(MainActivity.this, lat + " " + lang, Toast.LENGTH_SHORT).show(); 
     gps = new GPSPosition(MainActivity.this); 

    } 

    public void clickingBtn(View view) { 



     if (gps.canGetLocation()) { 

      double latitude = gps.getLatitude(); 
      lat = String.valueOf(latitude); 
      double longitude = gps.getLongitude(); 
      lang = String.valueOf(longitude); 
      Toast.makeText(MainActivity.this, latitude + " " + longitude, Toast.LENGTH_SHORT).show(); 
     } else { 

      gps.showSettingsAlert(); 
     } 

    } 

這是清單中的權限：

<uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> 
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> 

Answer 1

getLastKnownLocation()將返回null如果沒有該提供的最新位置數據。而且，即使它返回null以外的其他東西，Location也可能相當陳舊。在getLastKnownLocation()返回不可用的情況下，您將不得不等待直到調用onLocationChanged()，然後使用傳入該方法的Location。