App is crashing before it starts

Question

I'm creating a simple app with two NumberPickers used to select a certain number of minutes and seconds. There isn't too much code so I will post it here:

public class MainActivity extends Activity implements OnClickListener {

private static final String TAG = "Interval Trainer";
private CountDownTimer countDownTimer;
private boolean timerHasStarted = false;
private Button startButton;
public TextView text;
private final long interval = 1 * 1000;

//Create NumberPickers
NumberPicker numberPicker1 = (NumberPicker) findViewById(R.id.numberPicker1);
NumberPicker numberPicker2 = (NumberPicker) findViewById(R.id.numberPicker2);

@Override
protected void onCreate(Bundle savedInstanceState) {
    Log.i(TAG,"Entering onCreate()");
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    startButton = (Button) this.findViewById(R.id.button);
    startButton.setOnClickListener(this);
    text = (TextView) this.findViewById(R.id.timer);

    //Set min and max values for NumberPickers
    numberPicker1.setMaxValue(100);
    numberPicker1.setMinValue(0);
    numberPicker2.setMaxValue(59);  //This is the seconds picker
    numberPicker2.setMinValue(0);

    Log.i(TAG,"Exiting onCreate()");
}

@Override
public void onClick(View v) {
    //Calculate total time from NumberPickers in seconds
    long startTime = (numberPicker1.getValue() * 60) + numberPicker2.getValue();

    //Create CountDownTimer with values from NumberPickers
    countDownTimer = new MyCountDownTimer(startTime, interval);
    text.setText(text.getText() + String.valueOf(startTime / 1000));    //should be removed

    if(!timerHasStarted) {
        countDownTimer.start();
        timerHasStarted = true;
        startButton.setText("STOP");
    } else {
        countDownTimer.cancel();
        timerHasStarted = false;
        startButton.setText("RESTART");
    }

    //Disable the NumberPickers after 'Start' is pressed
    numberPicker1.setEnabled(false);
    numberPicker2.setEnabled(false);
}

public class MyCountDownTimer extends CountDownTimer {
    public MyCountDownTimer(long startTime, long interval) {
        super(startTime, interval);
    }

    @Override
    public void onFinish() {
        text.setText("Time's up!");
        //re-enable the NumberPickers once countdown is done
        numberPicker1.setEnabled(true);
        numberPicker2.setEnabled(true);
    }

    @Override
    public void onTick(long millisUntilFinished) {
        text.setText("" + millisUntilFinished / 1000);

        //Changes the value of the NumberPickers after each tick

    }
}
}

I have a feeling the crash is related to me declaring the two NumberPickers outside of any methods (this would automatically make them static?). Originally I had these two lines of code in my onCreate() but since I needed them in my inner class and other methods I moved it outside. Is this what is causing the crash? If so, how do I do this correctly and still have access to numberPicker1 and 2 all around my class (including inner class)?

Thank you!

Answer 1

You cant intiate object like this

//Create NumberPickers
NumberPicker numberPicker1 = (NumberPicker) findViewById(R.id.numberPicker1);
NumberPicker numberPicker2 = (NumberPicker) findViewById(R.id.numberPicker2);

after onCreate only you layout loads so you dont have you object yet initialized. You can initlize you object in onCreate after

setContentView(R.layout.activity_main);

For example

// init variable
NumberPicker numberPicker1 = null;
NumberPicker numberPicker2 = null;

@Override
protected void onCreate(Bundle savedInstanceState) {

    setContentView(R.layout.activity_main);
 // After here only your Activity gets the layout objects

    numberPicker1 = (NumberPicker) findViewById(R.id.numberPicker1);
    numberPicker2 = (NumberPicker) findViewById(R.id.numberPicker2);

}

Answer 2

You should put your findViewById inside onCreate method and create local variables:

// init variable
NumberPicker numberPicker1, numberPicker2;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // ...
    numberPicker1 = (NumberPicker) findViewById(R.id.numberPicker1);
    numberPicker2 = (NumberPicker) findViewById(R.id.numberPicker2);

}

Then, you will able to call these variables inside other methods. According to this reference:

Non-static nested classes (InnerClasses) have access to other members of the enclosing class, even if they are declared private. Static nested classes do not have access to other members of the enclosing class. [...] InnerClass has direct access to the methods and fields of its enclosing instance.