android - java.lang.RuntimeException 无法实例化服务 : java. lang.NullPointerException

Question

我试图创建一个启动服务的 Activity (在新线程中)。它包含一个布局，其中包含两个 editText 和一个名为 Send 的按钮。重点是当我执行 MainActivity 时，它会抛出:

06-15 22:32:13.312: E/AndroidRuntime(643): FATAL EXCEPTION: main
06-15 22:32:13.312: E/AndroidRuntime(643): java.lang.RuntimeException: Unable to instantiate service hikoki.services.NotificationsService: java.lang.NullPointerException
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.app.ActivityThread.handleCreateService(ActivityThread.java:2237)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.app.ActivityThread.access$1600(ActivityThread.java:123)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1201)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.os.Handler.dispatchMessage(Handler.java:99)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.os.Looper.loop(Looper.java:137)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.app.ActivityThread.main(ActivityThread.java:4424)
06-15 22:32:13.312: E/AndroidRuntime(643):  at java.lang.reflect.Method.invokeNative(Native Method)
06-15 22:32:13.312: E/AndroidRuntime(643):  at java.lang.reflect.Method.invoke(Method.java:511)
06-15 22:32:13.312: E/AndroidRuntime(643):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-15 22:32:13.312: E/AndroidRuntime(643):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-15 22:32:13.312: E/AndroidRuntime(643):  at dalvik.system.NativeStart.main(Native Method)
06-15 22:32:13.312: E/AndroidRuntime(643): Caused by: java.lang.NullPointerException
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.content.ContextWrapper.getSystemService(ContextWrapper.java:386)
06-15 22:32:13.312: E/AndroidRuntime(643):  at hikoki.services.NotificationsService.<init>(NotificationsService.java:35)
06-15 22:32:13.312: E/AndroidRuntime(643):  at java.lang.Class.newInstanceImpl(Native Method)
06-15 22:32:13.312: E/AndroidRuntime(643):  at java.lang.Class.newInstance(Class.java:1319)
06-15 22:32:13.312: E/AndroidRuntime(643):  at android.app.ActivityThread.handleCreateService(ActivityThread.java:2234)
06-15 22:32:13.312: E/AndroidRuntime(643):  ... 10 more

Main Activity的代码是这样的:

public class MainActivity extends Activity {
    private String TAG = getClass().getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Thread t= new Thread(){
            public void run(){
                Intent intent=new Intent(getContext(),NotificationsService.class);
                //Intent intent=new Intent("hikoki.services.NotificationsService");
                Log.d(TAG,"sending notificationsService");
                startService(intent);
            }
        };
        t.start();
    }

    protected Context getContext() {    
        return this;
    }
}

NotificationsService 的代码在这里:

public class NotificationsService extends IntentService{
    private static  int TIME_INTERVAL_MILIS=5000;
    private static final int REFRESH=10;
    private  NotificationManager noteManager;
    private static List<FlightStatusNote> flights= new ArrayList<FlightStatusNote>();

    public NotificationsService(){
        super("NotificationsService"); 
        noteManager= NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE)
    }
}

AndroidManifest 是这样的:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="hikoki.services"
    android:versionCode="1"
    android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="15"
    android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="hikoki.services.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <service android:name=".FlightStatusService"></service>
    <service android:enabled="true" android:name=".NotificationsService"></service>
</application>

</manifest>

Answer 1

你不能调用 getSystemService()来自初始值设定项(如您最初)或来自构造函数(如您现在)。请覆盖 onCreate() , 并调用 getSystemService()那里。

基本上，直到 onCreate()被调用(或者更准确地说，直到您从 super.onCreate() 调用 onCreate() 之后)，Service 上的继承方法尚未准备好供您使用。