在谷歌的官网上有一段重力感应示例代码，但我复制下来运行时却出现了错误，源代码如下：
- Java code
package com.sensor.test2;import android.app.Activity;import android.os.Bundle;import android.hardware.SensorManager;import android.hardware.Sensor;import android.hardware.SensorEventListener;import android.hardware.SensorEvent;public class SensorTest extends Activity implements SensorEventListener { private final SensorManager mSensorManager; private final Sensor mAccelerometer; public SensorTest() { mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE); mAccelerometer = mSensorManager .getDefaultSensor(Sensor.TYPE_ACCELEROMETER); } protected void onResume() { super.onResume(); mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL); } protected void onPause() { super.onPause(); mSensorManager.unregisterListener(this); } public void onAccuracyChanged(Sensor sensor, int accuracy) { } public void onSensorChanged(SensorEvent event) { }}出错的提示是这样的：
07-05 12:15:28.235: W/dalvikvm(11836): threadid=3: thread exiting with uncaught exception (group=0x40026268)
07-05 12:15:28.245: E/AndroidRuntime(11836): Uncaught handler: thread main exiting due to uncaught exception
07-05 12:15:28.265: E/AndroidRuntime(11836): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.sensor.test2/com.sensor.test2.SensorTest}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2417)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread.access$2200(ActivityThread.java:119)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.os.Handler.dispatchMessage(Handler.java:99)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.os.Looper.loop(Looper.java:123)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread.main(ActivityThread.java:4363)
07-05 12:15:28.265: E/AndroidRuntime(11836): at java.lang.reflect.Method.invokeNative(Native Method)
07-05 12:15:28.265: E/AndroidRuntime(11836): at java.lang.reflect.Method.invoke(Method.java:521)
07-05 12:15:28.265: E/AndroidRuntime(11836): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
07-05 12:15:28.265: E/AndroidRuntime(11836): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
07-05 12:15:28.265: E/AndroidRuntime(11836): at dalvik.system.NativeStart.main(Native Method)
07-05 12:15:28.265: E/AndroidRuntime(11836): Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.Activity.getSystemService(Activity.java:3468)
07-05 12:15:28.265: E/AndroidRuntime(11836): at com.sensor.test2.SensorTest.<init>(SensorTest.java:15)
07-05 12:15:28.265: E/AndroidRuntime(11836): at java.lang.Class.newInstanceImpl(Native Method)
07-05 12:15:28.265: E/AndroidRuntime(11836): at java.lang.Class.newInstance(Class.java:1479)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
07-05 12:15:28.265: E/AndroidRuntime(11836): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2409)
07-05 12:15:28.265: E/AndroidRuntime(11836): ... 11 more
请问这是怎么回事的呢？不仅是官网给出的代码，我还试了CSDN和其他社区中给出的相关代码，都是同样的错误~