android compass

使用传感器的关键点：
创建传感器管理器: private SensorManager mSensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
创建一个传感器：Sensor mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);
然后创建一个传感器事件监听器： private final SensorEventListener mListener = new SensorEventListener()
该传感器监听器有两个方法：public void onSensorChanged(SensorEvent event) public void onAccuracyChanged(Sensor sensor, int accuracy)
然后注册传感器侦听回调函数：mSensorManager.registerListener(mListener, mSensor, SensorManager.SENSOR_DELAY_GAME);
最后销毁传感器回调函数： mSensorManager.unregisterListener(mListener);

package com.example.compass;
import android.app.Activity;
import android.content.Context;
import android.graphics.*;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.Config;
import android.util.Log;
import android.view.View;

public class Compass extends Activity {

    private static final String TAG = "Compass";

    private SensorManager mSensorManager;//传感器管理器
    private Sensor mSensor; //传感器
    private SampleView mView;// view
    private float[] mValues;

    private final SensorEventListener mListener = new SensorEventListener() {
        public void onSensorChanged(SensorEvent event) {
            if (Config.DEBUG) Log.d(TAG,
                    "sensorChanged (" + event.values[0] + ", " + event.values[1] + ", " + event.values[2] + ")");
            mValues = event.values;
            if (mView != null) {
                mView.invalidate();
            }
        }

        public void onAccuracyChanged(Sensor sensor, int accuracy) {
        }
    };

    @Override
    protected void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        mSensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
        mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);
        mView = new SampleView(this);
        setContentView(mView);
    }

    @Override
    protected void onResume()
    {
        if (Config.DEBUG) Log.d(TAG, "onResume");
        super.onResume();

        mSensorManager.registerListener(mListener, mSensor,
                SensorManager.SENSOR_DELAY_GAME);
    }

    @Override
    protected void onStop()
    {
        if (Config.DEBUG) Log.d(TAG, "onStop");
        mSensorManager.unregisterListener(mListener);
        super.onStop();
    }

    private class SampleView extends View {
        private Paint   mPaint = new Paint();
        private Path    mPath = new Path();
        private boolean mAnimate;

        public SampleView(Context context) {
            super(context);

            // Construct a wedge-shaped path，设置指南针轮廓
            mPath.moveTo(0, -50);
            mPath.lineTo(-20, 80);
            mPath.lineTo(0, 50);
            mPath.lineTo(20, 80);
            mPath.close();
        }

        @Override protected void onDraw(Canvas canvas) {
            Paint paint = mPaint;

            canvas.drawColor(Color.WHITE);//设置canvas背景颜色

            paint.setAntiAlias(true);//设置抗锯齿
            paint.setColor(Color.BLACK);//设置paint的颜色
            paint.setStyle(Paint.Style.STROKE);//设置填充方式

            int w = canvas.getWidth();
            int h = canvas.getHeight();
            int cx = w / 2;
            int cy = h / 2;

            canvas.translate(cx, cy);//canvas平移到屏幕中间
            if (mValues != null) {
                canvas.rotate(-mValues[0]);
            }
            canvas.drawPath(mPath, mPaint);
        }

        @Override
        protected void onAttachedToWindow() {
            mAnimate = true;
            if (Config.DEBUG) Log.d(TAG, "onAttachedToWindow. mAnimate=" + mAnimate);
            super.onAttachedToWindow();
        }

        @Override
        protected void onDetachedFromWindow() {
            mAnimate = false;
            if (Config.DEBUG) Log.d(TAG, "onDetachedFromWindow. mAnimate=" + mAnimate);
            super.onDetachedFromWindow();
        }
    }
}