Android服务始终为null

Question

我正在尝试启动一项服务，但始终获得NPE。 我可能做错了什么？ 甚至onServiceConnected()方法也不会被调用，为什么呢？

    @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);
}

结果：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();
    }
}

当然，我在清单中也提供了该服务：

<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

意图似乎还可以：

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

Answer 1

您的堆栈跟踪清楚地显示了okButton()发生的NullPointerException ，根据您发布的代码，该函数中的唯一一行是

    startService(mServiceIntent);

因此很明显，尽管已在onCreate()设置了mServiceIntent ，但mServiceIntent还是null。

您还有其他设置mServiceIntent吗？

还是您有一个在其中调用okButton()的构造函数？ 我唯一想到的是构造函数将在onCreate()之前运行。 这也可以解释为什么即使在onCreate()调用onServiceConnected()也永远不会运行bindService() onCreate() 。

Answer 2

此代码不是正确的Java语法，因为方法定义没有返回类型：

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

您需要类似：

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

在我看来，从该堆栈跟踪okButton()方法是在onCreate（）方法之前创建MyActivity实例过程中被称为叫，当然在那个时候MSERVICE将是无效的。

发布更多代码或更正您发布的代码，以使其实际上与您使用的代码匹配。