android 速度仪表盘代码

以下是一个简单的 Android 速度仪表盘的代码示例，它使用 Android Sensor API 来监测加速度传感器和地球重力传感器的值，计算设备的速度并显示在屏幕上：

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.TextView;

public class SpeedometerActivity extends Activity implements SensorEventListener {
    
    private SensorManager sensorManager;
    private Sensor accelerometer;
    private Sensor gravity;
    private TextView speedView;
    private float[] lastAccelerometer = new float[3];
    private float[] lastGravity = new float[3];
    private long lastUpdateTime;
    private float currentSpeed = 0;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_speedometer);
        speedView = (TextView) findViewById(R.id.speedView);
        sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        gravity = sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY);
        lastUpdateTime = System.currentTimeMillis();
    }
    
    @Override
    protected void onResume() {
        super.onResume();
        sensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_NORMAL);
        sensorManager.registerListener(this, gravity, SensorManager.SENSOR_DELAY_NORMAL);
    }
    
    @Override
    protected void onPause() {
        super.onPause();
        sensorManager.unregisterListener(this);
    }
    
    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
            System.arraycopy(event.values, 0, lastAccelerometer, 0, 3);
        } else if (event.sensor.getType() == Sensor.TYPE_GRAVITY) {
            System.arraycopy(event.values, 0, lastGravity, 0, 3);
        }
        long currentTime = System.currentTimeMillis();
        if ((currentTime - lastUpdateTime) > 100) {
            float[] rotationMatrix = new float[9];
            float[] orientation = new float[3];
            SensorManager.getRotationMatrix(rotationMatrix, null, lastGravity, lastAccelerometer);
            SensorManager.getOrientation(rotationMatrix, orientation);
            float pitch = orientation[1];
            float speed = calculateSpeed(pitch);
            currentSpeed = (currentSpeed * 0.7f) + (speed * 0.3f);
            speedView.setText(String.format("%.1f km/h", currentSpeed));
            lastUpdateTime = currentTime;
        }
    }
    
    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        // Do nothing
    }
    
    private float calculateSpeed(float pitch) {
        float gravity = 9.81f;
        float acceleration = (float) Math.sin(pitch) * gravity;
        return acceleration * 3.6f;
    }
}

在这个示例中，我们首先获取加速度传感器和地球重力传感器的引用，然后在 `onResume` 方法中注册这两个传感器的监听器。在 `onSensorChanged` 方法中，我们获取传感器事件的值，并使用这些值计算设备的速度。最后，我们将计算出的速度显示在屏幕上。当应用程序暂停时，我们在 `onPause` 方法中注销传感器的监听器。