android - 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。我正在NullPointerException排队LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

HomeActivity 启动服务

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

Service (ForHire) 创建一个 TimerTask 更新

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.
    }

第一个问题是我得到了 NullPointerException。第二个问题是，如果我注释掉LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, God.KM20TIME, God.KM20DISTANCE, (LocationListener) this);这两行，则永远不会调用 onLocationChanged。

我的清单

<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>

我在这里想念什么？

编辑：Values of KM20TIME = 5000（5 秒）和KM20DISTANCE = 1（1 米）。除了下面的修复之外，我走出家门，启用 GPS，然后从阳台的一个角落走到另一个角落。我注意到我每 5 秒从一个角落走到另一个角落时，我的 gps (LSB) 会发生变化。

score 11 · Accepted Answer

您最早可以调用new Updates(getUpdatesNow);的是在您的服务onCreate()方法中。原因很简单，getSystemService()需要一个有效的 Context 在进入之前不存在onCreate()。

尝试：

private Timer getUpdatesNow;
private Updates updates;

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

score 3 · Accepted Answer

// 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);

score 2 · Accepted Answer

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

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

3 回答 3

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