调用getSystemService（Context.LOCATION_SERVICE）并且未调用onLocationChanged时出现NullpointerException

Question

我正在尝试创建一个更新当前gps位置的后台服务。我在第NullPointerException行<{1}}

HomeActivity启动服务

LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

Service（ForHire）创建一个TimerTask更新

startService(new Intent(getApplicationContext(), ForHire.class));

第一个问题是我得到了NullPointerException。 第二个问题是，如果我将这两行注释掉public class ForHire extends Service { ... private Timer getUpdatesNow = new Timer(); private Updates updates = new Updates(getUpdatesNow); @Override public void onCreate() { ... getUpdatesNow.schedule(updates, God.KM20TIME); Log.v("Taxeeta", "Notification created"); } private class Updates extends TimerTask implements LocationListener { private Timer getUpdatesNow; public Updates(Timer newGetUpdatesNow) { super(); getUpdatesNow = newGetUpdatesNow; LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, God.KM20TIME, God.KM20DISTANCE, (LocationListener) this); } public void run() { ... //do some cleanup } @Override public void onLocationChanged(Location location) { Log.v("Taxeeta", "Location changed"); // do a update of the current location. } ，则永远不会调用onLocationChanged。

我的清单

LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, God.KM20TIME, God.KM20DISTANCE, (LocationListener) this);

我在这里缺少什么？

编辑：<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.READ_PHONE_STATE" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> <uses-permission android:name="android.permission.CALL_PHONE" /> <application ...> ... <uses-library android:name="com.google.android.maps" /> </application> （5秒）和Values of KM20TIME = 5000（1米）。除了下面的修理，我走出了我的房子，启用了GPS，从阳台的一个角落走到另一个角落。我注意到我的gps（LSB）在每隔5秒钟从一个角落走到另一个角落时发生了变化。

Answer 1

您最早可以拨打new Updates(getUpdatesNow);的电话是在您的服务的onCreate()方法中。原因很简单，getSystemService()需要一个在进入onCreate()之前不存在的有效上下文。

尝试：

private Timer getUpdatesNow;
private Updates updates;

@Override
public void onCreate() {
    ...
    getUpdatesNow = new Timer();
    updates = new Updates(getUpdatesNow);

Answer 2

// Acquire a reference to the system Location Manager
LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

// Define a listener that responds to location updates
Location location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

if (location != null) {
    Toast.makeText(getBaseContext(),
                            "Last Location is found..",
                            Toast.LENGTH_LONG).show();  
} else {

    Toast.makeText(getBaseContext(),
                            "Last Location is not found..",
                            Toast.LENGTH_LONG).show();
}
LocationListener locationListener = new LocationListener() {
public void onStatusChanged(String provider,
    int status, Bundle extras) {
}
public void onProviderEnabled(String provider) {
    Toast.makeText(getApplicationContext(),
        "Gps Enabled", Toast.LENGTH_SHORT).show();
}
public void onProviderDisabled(String provider) {
    Toast.makeText(getApplicationContext(),
        "Gps Disabled", Toast.LENGTH_SHORT).show();
}

@Override
public void onLocationChanged(Location location) {
    Log.i("geolocation",
        "lat is : " + location.getLatitude()
        + " and " + location.getLongitude()
        + "");
    Toast.makeText(getBaseContext(),
    "Location is Changed..", Toast.LENGTH_LONG)
        .show();
}
};
// Register the listener with the Location Manager to receive location updates
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER, 0, 0,
locationListener);

Answer 3

@Override
public void onCreate() {
     new Updates(getUpdatesNow);
    ...
    getUpdatesNow.schedule(updates, God.KM20TIME);
    Log.v("Taxeeta", "Notification created");
}