Android ApiDemos 学习 Graphics->SensorTest

private final SensorEventListener mListener = new SensorEventListener() {

        private final float[] mScale = new float[] { 2, 2.5f, 0.5f };   // accel
        private float[] mPrev = new float[3];
        private long mLastGestureTime;

        public void onSensorChanged(SensorEvent event) {
            boolean show = false;
            float[] diff = new float[3];

            for (int i = 0; i < 3; i++) {
                diff[i] = Math.round(mScale[i] * (event.values[i] - mPrev[i]) * 0.45f);
                if (Math.abs(diff[i]) > 0) {
                    show = true;
                }
                mPrev[i] = event.values[i];
            }

            if (show) {
                // only shows if we think the delta is big enough, in an attempt
                // to detect "serious" moves left/right or up/down
                Log.e(TAG, "sensorChanged " + event.sensor.getName() +
                        " (" + event.values[0] + ", " + event.values[1] + ", " +
                        event.values[2] + ")" + " diff(" + diff[0] +
                        " " + diff[1] + " " + diff[2] + ")");
            }

            long now = android.os.SystemClock.uptimeMillis();
            if (now - mLastGestureTime > 1000) {
                mLastGestureTime = 0;

                float x = diff[0];
                float y = diff[1];
                boolean gestX = Math.abs(x) > 3;
                boolean gestY = Math.abs(y) > 3;

                if ((gestX || gestY) && !(gestX && gestY)) {
                    if (gestX) {
                        if (x < 0) { //好吧 检查设备的移动方向..
                            Log.e("test", "<<<<<<<< LEFT <<<<<<<<<<<<");
                        } else {
                            Log.e("test", ">>>>>>>>> RITE >>>>>>>>>>>");
                        }
                    } else {
                        if (y < -2) {
                            Log.e("test", "<<<<<<<< UP <<<<<<<<<<<<");
                        } else {
                            Log.e("test", ">>>>>>>>> DOWN >>>>>>>>>>>");
                        }
                    }
                    mLastGestureTime = now;
                }
            }
        }

        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_ACCELEROMETER);
        mView = new SampleView(this);
        setContentView(mView);
        if (Config.DEBUG) Log.d(TAG, "create " + mSensorManager);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(mListener, mSensor, SensorManager.SENSOR_DELAY_FASTEST);//注册的时机
        if (Config.DEBUG) Log.d(TAG, "resume " + mSensorManager);
    }

    @Override
    protected void onStop() {
        mSensorManager.unregisterListener(mListener);//释放的时机!!
        super.onStop();
        if (Config.DEBUG) Log.d(TAG, "stop " + mSensorManager);
    }

    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
            mPath.moveTo(0, -50);
            mPath.lineTo(-20, 60);
            mPath.lineTo(0, 50);
            mPath.lineTo(20, 60);
            mPath.close();
        }

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

            canvas.drawColor(Color.WHITE);

            paint.setAntiAlias(true);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.FILL);

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

            canvas.translate(cx, cy);
            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, "onAttachedToWindow. mAnimate="+mAnimate);
            super.onDetachedFromWindow();
        }
    }
}

sf

本例SensorTest和例子Android ApiDemos示例解析(61):Graphics->Compass在绘图方面的介绍基本一样，我也不知道为什么Google
再把这个SensorTest还是归在Graphics 目录下。

本例着重点是介绍使用SensorManager.SENSOR_ACCELEROMETER 如何来判断设备的移动方向：使用Log的方式而非图形的方式显示结果，所以运行本例显示的箭头始终向上。

本例归在Hardware比较合理。如何使用SENSOR_ACCELEROMETER判断设备移动方向的代码如下：

[java] view
plaincopyprint?

public void onSensorChanged(int sensor, float[] values) {

boolean show = false;

float[] diff = new float[3];



for (int i = 0; i < 3; i++) {

diff[i] = Math.round(mScale[i]

* (values[i] - mPrev[i]) * 0.45f);

if (Math.abs(diff[i]) > 0) {

show = true;

}

mPrev[i] = values[i];

}



...



long now = android.os.SystemClock.uptimeMillis();

if (now - mLastGestureTime > 1000) {

mLastGestureTime = 0;



float x = diff[0];

float y = diff[1];

boolean gestX = Math.abs(x) > 3;

boolean gestY = Math.abs(y) > 3;



if ((gestX || gestY) && !(gestX && gestY)) {

if (gestX) {

if (x < 0) {

android.util.Log.e("test",

"<<<<<<<< LEFT <<<<<<<<<<<<");

} else {

android.util.Log.e("test",

">>>>>>>>> RITE >>>>>>>>>>>");

}

} else {

if (y < -2) {

android.util.Log.e("test",

"<<<<<<<< UP <<<<<<<<<<<<");

} else {

android.util.Log.e("test",

">>>>>>>>> DOWN >>>>>>>>>>>");

}

}

mLastGestureTime = now;

}

}

}

如果想在设备移动时，屏幕上箭头的指向随着变化，可以参见Compass的例子，加上：

[java] view
plaincopyprint?

mValues = values;

if (mView != null) {

mView.invalidate();