android中的位置為null

Question

我正在嘗試獲取我的位置。 但是我所擁有的只是零。 請看下面的代碼：

 public class ListBranchesActivity extends Activity {       

    private double lat, lon;

    private LocationManager lm;
    private Location location;

    private final LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(Location location) {
            lon = location.getLongitude();
            lat = location.getLatitude();
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderEnabled(String provider) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderDisabled(String provider) {
            // TODO Auto-generated method stub

        }
    };

然后在onCreate()某處：

lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 2000, 10,
                locationListener);
        location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

以下代碼返回NullPointerException：

   Log.w("es09", "coordinates are " + lon + " " + lat +" " +location.getLatitude()+" "+ location.getLongitude());

該代碼返回“坐標為0.0 0.0”

 Log.w("es09", "coordinates are " + lon + " " + lat);

我的清單權限：

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
   <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
   <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
   <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
   <uses-permission android:name="android.permission.INTERNET" />
   <uses-permission android:name="android.permission.CALL_PHONE" />
   <uses-permission android:name="android.permission.READ_PHONE_STATE"/>
   <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
   <uses-permission android:name="android.permission.ACCESS_GPS"/>
   <uses-permission android:name="android.permission.ACCESS_LOCATION"/>
   <uses-permission android:name="android.permission.ACCESS_ASSISTED_GPS"/>

怎么了？

Answer 1

問題是您假設總是找回位置，但事實並非如此。 沒有保證將位置退還給您，因此您必須檢查是否為空。

運用

lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

不能保證最后一個位置存在，只要您得到一個位置，就應始終檢查以確保它不為空。

Answer 2

使用NETWORK_PROVIDER來獲取位置，因為很多時候GPS都會給出空的緯度和經度

m_locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,0,0, this);
    m_location = m_locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

在清單中添加以下權限

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />