android: light sensor nullPointerException

Question

In my activity I have one TextView called "senzosv". I want it to show current value from my light sensor. I have following code.

public class Osvetlenie extends Activity implements OnItemSelectedListener, OnSeekBarChangeListener, SensorEventListener  {


SensorManager sm;
Sensor proxSensor;
Sensor lighhtSens;
TextView tv = (TextView)findViewById(R.id.senzosv);

This is in my onCreate:

 ...
sm = (SensorManager) getSystemService(SENSOR_SERVICE);
    proxSensor =sm.getDefaultSensor(Sensor.TYPE_PROXIMITY);
    lighhtSens = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
    sm.registerListener(this, proxSensor, SensorManager.SENSOR_DELAY_NORMAL);
    sm.registerListener(this, lighhtSens, SensorManager.SENSOR_DELAY_NORMAL);

And here are methods onSensorChanged and onAccuracyChanged

 public void onSensorChanged(SensorEvent event) 
{
if( event.sensor.getType() == Sensor.TYPE_LIGHT)
    {
    tv.setText("value: " + event.values[0] + " lux" );   
    Toast.makeText(getApplicationContext(),"On SensorChanged"+ event.values[0],Toast.LENGTH_SHORT).show();

    }

}

public void onAccuracyChanged(Sensor sensor, int accuracy) {

    Log.d(ACCESSIBILITY_SERVICE,"onAccuracyChanged: " + sensor + ", accuracy: " + accuracy);
    if(sensor.getType() == Sensor.TYPE_LIGHT){
        Log.i("Sensor Changed", "Accuracy :" + accuracy);
       }

}

When I run my application, and when I am trying to start this activity, I get nullpointexception in LogCat and error message: application unexpectedly closed I am testing my app on Samsung Galaxy S II (GT-I9100) What did I wrong? Thank you :)

Answer 1

do this

tv = (TextView)findViewById(R.id.senzosv);

after setContentView()

Answer 2

You can only use findViewById after you have setContentView.

i.e. move it into onCreate after setContentView

TextView tv;

public void onCreate(Bundle b){
   super.onCreate(b);
   setContentView(R.layout.activity_main);

   tv = (TextView) findViewById(R.id.senzosv);

}

---

If you read your LogCat a bit more carefully it will explain what line of your code is causing the NullPointer and you could debug it easier.

---

You will also need permissions in your manifest to use the sensor.

Answer 3

You must call setContentView(R.layout.layout_main); because Its set the activity layout then get the textview reference.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layout_main);
    tv = (TextView)findViewById(R.id.senzosv);
}

Is light sensor able to return only values 1000, 100 and 10?

Directly get value from the system device file

Scanner st = new Scanner(new File("/sys/devices/virtual/lightsensor/switch_cmd/lightsensor_file_state"));
int lux = st.nextInt();
st.close();