从服务调用线程

Question

我可以从服务启动线程吗？

我想记录正在进行的音频信号并在我的应用程序中检测到哨声，即使在应用程序关闭后也应该运行。对于这个应用程序，我有两个线程，一个是连续录制音频，另一个是检测哨子（我使用了musicg库中的代码）。现在我正在使用服务，以便整个功能始终在后台运行，服务正在调用这两个线程，如下面的代码所示。 问题：一旦启动了应用程序并启动了服务，如果我关闭了应用程序，则会引发错误。

代码：

`package com.musicg.demo.android; 

import android.app.ActivityManager; 
import android.app.Service; 
import android.app.admin.DevicePolicyManager; 
import android.content.ComponentName; 
import android.content.Context; 
import android.content.Intent; 
import android.os.IBinder; 
import android.util.Log; 

public class DetectAndLockService extends Service implements 
     OnSignalsDetectedListener { 

    private DetectorThread detectorThread; 
    private RecorderThread recorderThread; 
    private DevicePolicyManager deviceManger; 
    private ActivityManager activityManager; 
    private ComponentName compName; 

    @Override 
    public IBinder onBind(Intent arg0) { 
     // TODO Auto-generated method stub 
     return null; 
    } 

    @Override 
    public void onCreate() { 
     super.onCreate(); 
    } 

    @Override 
    public void onStart(Intent intent, int startId) { 
     super.onStart(intent, startId); 
    } 

    @Override 
    public int onStartCommand(Intent intent, int flags, int startId) { 
     super.onStartCommand(intent, flags, startId); 

     deviceManger = (DevicePolicyManager) getSystemService(Context.DEVICE_POLICY_SERVICE); 
     activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE); 
     compName = new ComponentName(this, MyAdmin.class); 

     if (VariableClass.get_detection_running()) { 
      recorderThread = new RecorderThread(); 
      recorderThread.start(); 
      detectorThread = new DetectorThread(recorderThread); 
      detectorThread.setOnSignalsDetectedListener(DetectAndLockService.this); 
      detectorThread.start(); 
     } else { 
      recorderThread.stopRecording(); 
      detectorThread.stopDetection(); 
     } 
     return (START_STICKY); 
    } 

    @Override 
    public void onWhistleDetected() {  

     /*Action to be performed*/ 
    } 

    @Override 
    public void onDestroy() { 
     super.onDestroy(); 
     recorderThread.stopRecording(); 
     detectorThread.stopDetection();  
     System.out.println("Service is destroyed"); 
    } 


} 
` 

的logcat：

` 
11-27 17:01:14.843: W/dalvikvm(6206): threadid=1: thread exiting with uncaught exception (group=0x409f41f8) 
11-27 17:01:14.853: E/AndroidRuntime(6206): FATAL EXCEPTION: main 
11-27 17:01:14.853: E/AndroidRuntime(6206): java.lang.RuntimeException: Unable to start service com.musicg.demo.android.DetectAndLockService@4105d438 with null: java.lang.NullPointerException 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2376) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.app.ActivityThread.access$1900(ActivityThread.java:123) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.os.Handler.dispatchMessage(Handler.java:99) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.os.Looper.loop(Looper.java:137) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at java.lang.reflect.Method.invokeNative(Native Method) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at java.lang.reflect.Method.invoke(Method.java:511) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at dalvik.system.NativeStart.main(Native Method) 
11-27 17:01:14.853: E/AndroidRuntime(6206): Caused by: java.lang.NullPointerException 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at com.musicg.demo.android.DetectAndLockService.onStartCommand(DetectAndLockService.java:52) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2359) 
11-27 17:01:14.853: E/AndroidRuntime(6206):  ... 10 more 

` 

我要去哪里错了？

Answer 1

如果VariableClass.get_detection_running()方法的返回false那么你不检查null或调用方法之前初始化都recorderThread和detectorThread实例。所以你得到NullPointerException做到这一点：

if (VariableClass.get_detection_running()) { 
     ///...your code here.. 
    } else { 
     if(null !=recorderThread) 
     recorderThread.stopRecording(); 
     if(null !=detectorThread 
     detectorThread.stopDetection(); 
    } 

Answer 2

您必须执行此操作AsyncTask。 http://developer.android.com/reference/android/os/AsyncTask.html

您必须重新实现doInBackground方法。