Android服務始終為null

Question

我正在嘗試啟動一項服務，但始終獲得NPE。 我可能做錯了什么？ 甚至onServiceConnected()方法也不會被調用，為什么呢？

    @Override
    protected void onCreate(Bundle savedInstanceState) {
       mServiceIntent = new Intent(this, MyService.class);
       bindService(mServiceIntent, mConnection, Context.BIND_AUTO_CREATE);
       //other stuff
    }

用法：

private okButton(View v) {
    startService(mServiceIntent);
}

結果：NullPointerException！

private ServiceConnection mConnection = new ServiceConnection() {
          @Override
          public void onServiceConnected(ComponentName className, IBinder service) {
               Log.v("service", "gets never executed!");
               mDownloadService = ((LocalBinder<MyService>) service).getService();
            }

        @Override
            public void onServiceDisconnected(ComponentName className) {
            }
        };
}

public class LocalBinder<S> extends Binder {
    private String TAG = "LocalBinder";
    private  WeakReference<S> mService;


    public LocalBinder(S service){
        mService = new WeakReference<S>(service);
    }


    public S getService() {
        return mService.get();
    }
}

當然，我在清單中也提供了該服務：

<service android:enabled="true" android:name=".service.MyService" />

Logcat：

06-06 23:48:20.411: W/dalvikvm(592): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
06-06 23:48:20.461: E/AndroidRuntime(592): FATAL EXCEPTION: main
06-06 23:48:20.461: E/AndroidRuntime(592): java.lang.RuntimeException: Unable to start activity ComponentInfo{MyActivity}: java.lang.NullPointerException
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.os.Handler.dispatchMessage(Handler.java:99)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.os.Looper.loop(Looper.java:137)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread.main(ActivityThread.java:4424)
06-06 23:48:20.461: E/AndroidRuntime(592):  at java.lang.reflect.Method.invokeNative(Native Method)
06-06 23:48:20.461: E/AndroidRuntime(592):  at java.lang.reflect.Method.invoke(Method.java:511)
06-06 23:48:20.461: E/AndroidRuntime(592):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-06 23:48:20.461: E/AndroidRuntime(592):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-06 23:48:20.461: E/AndroidRuntime(592):  at dalvik.system.NativeStart.main(Native Method)
06-06 23:48:20.461: E/AndroidRuntime(592): Caused by: java.lang.NullPointerException
06-06 23:48:20.461: E/AndroidRuntime(592):  at MyActivity.okButton(MyActivity.java:217)
06-06 23:48:20.461: E/AndroidRuntime(592):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1939)
06-06 23:48:20.461: E/AndroidRuntime(592):  ... 11 more

意圖似乎還可以：

Log.v("service", String.valueOf(mServiceIntent == null)); //false

Answer 1

您的堆棧跟蹤清楚地顯示了okButton()發生的NullPointerException ，根據您發布的代碼，該函數中的唯一一行是

    startService(mServiceIntent);

因此很明顯，盡管已在onCreate()設置了mServiceIntent ，但mServiceIntent還是null。

您還有其他設置mServiceIntent嗎？

還是您有一個在其中調用okButton()的構造函數？ 我唯一想到的是構造函數將在onCreate()之前運行。 這也可以解釋為什么即使在onCreate()調用onServiceConnected()也永遠不會運行bindService() onCreate() 。

Answer 2

此代碼不是正確的Java語法，因為方法定義沒有返回類型：

private okButton(View v) {
    startService(mServiceIntent);
}

您需要類似：

private void okButton(View v) {
    startService(mServiceIntent);
}

在我看來，從該堆棧跟蹤okButton()方法是在onCreate（）方法之前創建MyActivity實例過程中被稱為叫，當然在那個時候MSERVICE將是無效的。

發布更多代碼或更正您發布的代碼，以使其實際上與您使用的代碼匹配。