我正在用nexus5xapi29在android工作室做一个step counter项目。我需要用传感器来做这个。我写的传感器代码如下，但它仍然给'传感器未找到'错误。有什么办法解决这个问题吗？

public class MainActivity extends AppCompatActivity implements SensorEventListener {
TextView tv_steps;
SensorManager sensorManager;
Sensor sensor;
boolean running = false;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate ( savedInstanceState );
    setContentView ( R.layout.activity_main );
    tv_steps = (TextView) findViewById ( R.id.tv_steps );

    sensorManager = (SensorManager) getSystemService ( Context.SENSOR_SERVICE);
}

@Override
protected void onResume() {
    super.onResume ();
    running = true;
    Sensor countSensor = sensorManager.getDefaultSensor ( sensor.TYPE_STEP_COUNTER );
    if(countSensor!= null){
        sensorManager.registerListener ( this,countSensor,SensorManager.SENSOR_DELAY_UI );
    }else {
        Log.d ("Main Activity","SENSOR NOT FOUND" );
    }
}

@Override
protected void onPause() {
    super.onPause ();
    running = false;
    //if you unregister the hardware will stop detecting steps
}

@Override
public void onSensorChanged(SensorEvent event) {

    if (running){
        tv_steps.setText ( String.valueOf ( event.values[0] ) );
    }

}

@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {

}

}
在manifest文件中，我还嵌入如下权限：

<uses-permission android:name="android.permission.ACTIVITY_RECOGNITION" android:required="true"/>