Android传感器API之：磁场Magnetic Field源码与示例

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); 
               } 
       } 

}

在Rexsee的社区找了个指南针实例开发的帖子，原文供参考：http://www.rexsee.com/CN/bbs/thread/2011-10-09/78.html
先找罗盘图片；打开传感器rexseeOrientation.start()；把方向改变时触发的事件写上：然后是处理图片。搞定~~

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)";
}

Rexsee是和PhoneGap类似的？有谁了解啊？

开源协议不靠谱，使用Rexsee要谨慎，当心被圈进去。