无法运行后台服务 [英] Cant run background service
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问题描述
我试图每次在后台服务中使用LocationListener类接收用户的当前位置，然后将其与数据库中存储的某些数据进行比较.但是当我尝试这样做时，我就错了
I am trying to use LocationListener class in a background service to receive the current location of user every time and then comparing it with some data stored in my database. but I am gettin error, when I am trying to do that
package com.example.alert;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.IBinder;
import android.widget.Toast;
public class service extends Service{
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
@Override
public IBinder onBind(Intent arg0) {
// TODO Auto-generated method stub
return null;
}
public void onCreate() {
Toast.makeText(this, "Background Service Created", Toast.LENGTH_LONG).show();
}
public void onDestroy() {
Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
}
public void onStart(Intent intent, int startid) {
Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show();
Intent myIntent=new Intent(service.this,CurrentLocation.class);
startActivity(myIntent);
}
}
这是我的日志
11-10 04:54:54.819: E/AndroidRuntime(768): FATAL EXCEPTION: main
11-10 04:54:54.819: E/AndroidRuntime(768): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.alert/com.example.alert.service}: java.lang.NullPointerException
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.access$600(ActivityThread.java:130)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.os.Handler.dispatchMessage(Handler.java:99)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.os.Looper.loop(Looper.java:137)
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.main(ActivityThread.java:4745)
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.reflect.Method.invokeNative(Native Method)
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.reflect.Method.invoke(Method.java:511)
11-10 04:54:54.819: E/AndroidRuntime(768): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-10 04:54:54.819: E/AndroidRuntime(768): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-10 04:54:54.819: E/AndroidRuntime(768): at dalvik.system.NativeStart.main(Native Method)
11-10 04:54:54.819: E/AndroidRuntime(768): Caused by: java.lang.NullPointerException
11-10 04:54:54.819: E/AndroidRuntime(768): at android.content.ContextWrapper.getSystemService(ContextWrapper.java:416)
11-10 04:54:54.819: E/AndroidRuntime(768): at com.example.alert.service.<init>(service.java:15)
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.Class.newInstanceImpl(Native Method)
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.Class.newInstance(Class.java:1319)
这是位置侦听器的其余代码
Here's the rest of the code of location listener
package com.example.alert;
import android.app.Activity;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.widget.Toast;
public class CurrentLocation extends Activity {
LocationManager lm ;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
/* Use the LocationManager class to obtain GPS locations */
LocationListener ll = new MyLocationListener();
//lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 5*60*10000, 0, ll);
lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0, 0, ll);
}
/* Class My Location Listener */
public class MyLocationListener implements LocationListener
{
public void onLocationChanged(Location loc)
{
if(loc!=null)
{
double x;
String Text = "My current location is: " +"Latitud = " + loc.getLatitude() +"Longitud = " + loc.getLongitude();
Toast.makeText( getApplicationContext(),Text,Toast.LENGTH_SHORT).show();
//for loop, alerters retrieving one by one
//x= calcDistance(loc.getLatitude(),loc.getLongitude(),,);
//if(x<1)
// distance < 1, retrieve data from DB and trigger
}
}
public void onProviderDisabled(String provider)
{
Toast.makeText( getApplicationContext(),"Gps Disabled - @From :Alert Me",Toast.LENGTH_SHORT ).show();
}
public void onProviderEnabled(String provider)
{
Toast.makeText( getApplicationContext(),"Gps Enabled - @From :Alert Me",Toast.LENGTH_SHORT).show();
}
public void onStatusChanged(String provider, int status, Bundle extras)
{
}
}/* End of Class MyLocationListener */
public double calcDistance(double latA, double longA, double latB, double longB) {
double theDistance = (Math.sin(Math.toRadians(latA)) * Math.sin(Math.toRadians(latB)) + Math.cos(Math.toRadians(latA)) * Math.cos(Math.toRadians(latB)) * Math.cos(Math.toRadians(longA - longB)));
return new Double((Math.toDegrees(Math.acos(theDistance))) * 69.09*1.6093);
}
}
清单文件
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.alert"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="15" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Instructions" android:label="Instructions"></activity>
<activity android:name=".AboutApp" android:label="About ALERT ME!"></activity>
<activity android:name=".ViewAlerters" android:label="Alerters Active"></activity>
<activity android:name=".AddAlerter" android:label="Add an Alerter"></activity>
<activity android:name=".EditAlerter" android:label="Edit an alerter"></activity>
<activity android:name=".AddLocation" android:label="Add Location to Alerter"></activity>
<activity android:name=".AddTrigger" android:label="Add trigger to Alerter"></activity>
<activity android:name=".SilVib" android:label="Silent/Vibrate Trigger"></activity>
<activity android:name=".CallMode" android:label="Call Mode Trigger"></activity>
<activity android:name=".service"></activity>
<activity android:name=".Status_Notify"></activity>
<activity android:name=".Notifier"></activity>
<activity android:name=".Message"></activity>
<activity android:name=".Message_sent"></activity>
<activity android:name=".StoringEntire"></activity>
<activity android:name=".CurrentLocation"></activity>
<uses-library android:name="com.google.android.maps"/>
<service
android:enabled="true"
android:name=".service"/>
</application>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.SEND_SMS"/>
<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_BACKGROUND_SERVICE"/>
</manifest>
推荐答案
LogCat指出:
Caused by: java.lang.NullPointerException
at android.content.ContextWrapper.getSystemService(ContextWrapper.java:416)
at com.example.alert.service.<init>(service.java:15)
通过将这段代码移到 onCreate()中，只需等待Context的初始化:
Simply wait for the Context to be initialized by moving this code into onCreate():
public class service extends Service {
LocationManager lm;
@Override
public void onCreate() {
// This line needs an existing context
lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Toast.makeText(this, "Background Service Created", Toast.LENGTH_LONG).show();
}
// etc
这篇关于无法运行后台服务的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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