How to use Sensors on Android?

Question

I'm a newbie, and I don't understand at all how to use the sensors. My goal is just for the moment to get the data of the rotation sensor on an Activity. I would use Rotation vectors, but I've seen here that they were no longer available on android 4.1.2... The code I have so far :

package thomas.drone;

import android.app.Activity;
import android.content.Intent;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends Activity implements View.OnClickListener {
    public Button boutonPilote;
    TextView xminus=null;
    TextView yminus=null;
    TextView xplus=null;
    TextView yplus = null;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    /*On déclare les capteurs que l'on veut utiliser*/
    SensorManager sMgr;
    sMgr = (SensorManager)this.getSystemService(SENSOR_SERVICE);
    Sensor motion;
    motion = sMgr.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR); //Ici un type Vecteur de rotation

    /**Permet de faire du Full screen sans activity spéciale*/
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.activity_main);

      /*On va relier les textes du layout aux valeurs de nos TextViews*/
    xminus = (TextView) findViewById(R.id.xminus);
    yminus = (TextView) findViewById(R.id.yminus);
    xplus = (TextView) findViewById(R.id.xplus);
    yplus = (TextView) findViewById(R.id.yplus);

    /*** On écoute le bouton Pilote/auto, qui switch d'une activité à l'autre**/
    boutonPilote = (Button) findViewById(R.id.bpilote);
    boutonPilote.setOnClickListener(this);

    /* et on active/enregistre le capteur*/
    sMgr.registerListener((android.hardware.SensorEventListener) this, motion,SensorManager.SENSOR_DELAY_NORMAL);


}

public void onAccuracyChanged(Sensor sensor, int accuracy) {

}
public void onSensorChanged(SensorEvent event) {
    Toast.makeText(getApplicationContext(), "Ca marche !", Toast.LENGTH_LONG).show();
}

@Override
public void onClick(View v) {
    Intent i1 = new Intent(this, ModeAuto.class);
    this.startActivity(i1);
}
}

Sorry for the commentaries, I'm french (nobody's perfect :) But the app crashes...

Here's the xml file, but I don't think that the problem comes from it :`

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/xminus"
    android:layout_toStartOf="@+id/yplus"
    android:layout_marginRight="43dp"
    android:typeface="monospace"
    android:textSize="14sp"
    android:textColor="@color/blanc"
    android:text="@string/xmoins"
    android:layout_alignBaseline="@+id/xplus"
    android:layout_alignBottom="@+id/xplus"
    android:layout_toLeftOf="@+id/yplus" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceSmall"
    android:id="@+id/yminus"
    android:typeface="monospace"
    android:textSize="14sp"
    android:textColor="@color/blanc"
    android:text="@string/yminus"
    android:layout_alignBottom="@+id/bdecollage"
    android:layout_alignLeft="@+id/yplus"
    android:layout_alignStart="@+id/yplus" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceSmall"
    android:id="@+id/xplus"
    android:layout_toEndOf="@+id/yminus"
    android:typeface="monospace"
    android:textSize="14sp"
    android:textColor="@color/blanc"
    android:text="@string/xplus"
    android:layout_toStartOf="@+id/bleft"
    android:layout_alignTop="@+id/bleft"
    android:layout_toLeftOf="@+id/bleft" />

`

Thank you, Thomas

Answer 1

Doing this

sMgr.registerListener((android.hardware.SensorEventListener) this, ....

is in many cases quite dangerous and it probably causes your crashes. You have to implement interface SensorEventListener and then implement particular methods.

Your Activity class should then look like this:

public class MainActivity extends Activity implements View.OnClickListener, SensorEventListener {

  // ...

  @Override
  public void onSensorChanged(SensorEvent event) {
   // ...
  }

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

  }
}

Next problem is, you don't know difference between @+id/bleft and @id/bleft. Definition with plus symbol creates new identifier with given name. Use it only at first occurence in xml file. In other cases omit plus symbol.