Android传感器API之：磁场Magnetic Field源码与示例：报错

Android的磁场传感器，Magnetic Field。。读取磁场的变化，通过该传感器可开发出指南针、罗盘等磁场应用。该传感器读取的数据是空间坐标系三个方向的磁场值，其数据单位为uT，即微特斯拉。

如下是Rexsee针对于磁场传感功能的扩展API源码，基于此可以在其平台上通过JS实现调用。文末补充了一个指南针应用的代码，相当的简单。。

/* 
* Copyright (C) 2011 The Rexsee Open Source Project 
* 
* Licensed under the Rexsee License, Version 1.0 (the "License"); 
* you may not use this file except in compliance with the License. 
* You may obtain a copy of the License at 
* 
*      http://www.rexsee.com/CN/legal/license.html 
* 
* Unless required by applicable law or agreed to in writing, software 
* distributed under the License is distributed on an "AS IS" BASIS, 
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
* See the License for the specific language governing permissions and 
* limitations under the License. 
*/ 
 
package rexsee.sensor;  
 
import rexsee.core.browser.JavascriptInterface;  
import rexsee.core.browser.RexseeBrowser;  
import android.content.Context;  
import android.hardware.Sensor;  
import android.hardware.SensorEvent;  
import android.hardware.SensorEventListener;  
import android.hardware.SensorManager;  
 
public class RexseeSensorMagneticField implements JavascriptInterface {  
 
       private static final String INTERFACE_NAME = "MagneticField";  
       @Override  
       public String getInterfaceName() {  
               return mBrowser.application.resources.prefix + INTERFACE_NAME;  
       }  
       @Override  
       public JavascriptInterface getInheritInterface(RexseeBrowser childBrowser) {  
               return this;  
       }  
       @Override  
       public JavascriptInterface getNewInterface(RexseeBrowser childBrowser) {  
               return new RexseeSensorMagneticField(childBrowser);  
       }  
 
       public static final String EVENT_ONMAGNETICFIELDCHANGED = "onMagneticFieldChanged";  
 
       private final Context mContext;  
       private final RexseeBrowser mBrowser;  
       private final SensorManager mSensorManager;  
       private final SensorEventListener mSensorListener;  
       private final Sensor mSensor;  
 
       private int mRate = SensorManager.SENSOR_DELAY_NORMAL;  
       private int mCycle = 100; //milliseconds  
       private int mEventCycle = 100; //milliseconds  
 
       private float mAccuracyX = 0;  
       private float mAccuracyY = 0;  
       private float mAccuracyZ = 0;  
 
       private long lastUpdate = -1;  
       private long lastEvent = -1;  
 
       private float x = -999f;  
       private float y = -999f;  
       private float z = -999f;  
 
       public RexseeSensorMagneticField(RexseeBrowser browser) {  
               mContext = browser.getContext();  
               mBrowser = browser;  
               browser.eventList.add(EVENT_ONMAGNETICFIELDCHANGED);  
 
               mSensorManager = (SensorManager) mContext.getSystemService(Context.SENSOR_SERVICE);  
 
               mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);  
 
               mSensorListener = new SensorEventListener() {  
                       @Override  
                       public void onAccuracyChanged(Sensor sensor, int accuracy) {  
                       }  
                       @Override  
                       public void onSensorChanged(SensorEvent event) {  
                               if (event.sensor.getType() != Sensor.TYPE_MAGNETIC_FIELD) return;  
                               long curTime = System.currentTimeMillis();  
                               if (lastUpdate == -1 || (curTime - lastUpdate) > mCycle) {  
                                       lastUpdate = curTime;  
                                       float lastX = x;  
                                       float lastY = y;  
                                       float lastZ = z;  
                                       x = event.values[SensorManager.DATA_X];  
                                       y = event.values[SensorManager.DATA_Y];  
                                       z = event.values[SensorManager.DATA_Z];  
                                       if (lastEvent == -1 || (curTime - lastEvent) > mEventCycle) {  
                                               if (  
                                                               (mAccuracyX >= 0 && Math.abs(x - lastX) > mAccuracyX)  
                                                                               || (mAccuracyY >= 0 && Math.abs(y - lastY) > mAccuracyY)  
                                                                               || (mAccuracyZ >= 0 && Math.abs(z - lastZ) > mAccuracyZ)  
                                                       ) {  
                                                               lastEvent = curTime;  
                                                               mBrowser.eventList.run(EVENT_ONMAGNETICFIELDCHANGED);  
                                                       }  
                                               }  
                                       }  
                               }  
               };  
 
       }  
 
       public String getLastKnownX() {  
               return (x == -999) ? "null" : String.valueOf(x);  
       }  
       public String getLastKnownY() {  
               return (y == -999) ? "null" : String.valueOf(y);  
       }  
       public String getLastKnownZ() {  
               return (z == -999) ? "null" : String.valueOf(z);  
       }  
 
       public void setRate(String rate) {  
               mRate = SensorRate.getInt(rate);  
       }  
       public String getRate() {  
               return SensorRate.getString(mRate);  
       }  
       public void setCycle(int milliseconds) {  
               mCycle = milliseconds;  
       }  
       public int getCycle() {  
               return mCycle;  
       }  
       public void setEventCycle(int milliseconds) {  
               mEventCycle = milliseconds;  
       }  
       public int getEventCycle() {  
               return mEventCycle;  
       }  
       public void setAccuracy(float x, float y, float z) {  
               mAccuracyX = x;  
               mAccuracyY = y;  
               mAccuracyZ = z;  
       }  
       public float getAccuracyX() {  
               return mAccuracyX;  
       }  
       public float getAccuracyY() {  
               return mAccuracyY;  
       }  
       public float getAccuracyZ() {  
               return mAccuracyZ;  
       }  
 
       public boolean isReady() {  
               return (mSensor == null) ? false : true;  
       }  
       public void start() {  
               if (isReady()) {  
                       mSensorManager.registerListener(mSensorListener, mSensor, mRate);  
               } else {  
                       mBrowser.exception(getInterfaceName(), "Magnetic-field sensor is not found.");  
               }  
       }  
       public void stop() {  
               if (isReady()) {  
                       mSensorManager.unregisterListener(mSensorListener);  
               }  
       }  
 
} 

function onOrientationChanged(){   //方向传感器事件,即当方向发生改变时触发的动作
  var x = rexseeOrientation.getLastKnownX();
  x = 90 - x;
  document.getElementById('oriDiv').style.webkitTransform = 'rotate('+x+"deg)";
}