CODEWITHSUNDEEP
android
MalteKlg1
MalteKlg1

Reputation: 57

Android - chronometer start and stop

I want to create a chronometer which I can start and stop with one button. With my code below I just get a nullpointer exception. How can I avoid it, or set the two functions to the button anyway?

public class MainActivity extends ActionBarActivity {
  Chronometer focus;
  Button start, stop, reset;
  long timeElapsed = SystemClock.elapsedRealtime() - focus.getBase();
  int x;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    timeElapsed = x;
    start = (Button) findViewById(R.id.button1);       
    focus = (Chronometer) findViewById(R.id.chronometer1);

    start.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            if(x == 0){
            focus.start();
            }

            if(x != 0){
            focus.stop();    
            }
        }
    });

}

}

Upvotes: 1

Views: 1158

Answers (2)

Ali
Ali

Reputation: 859

You are using variables before they are initialized. 'focus' and 'x' are used before they are initialized. Use this code instead to avoid nullpointer exception:

     public class MainActivity extends ActionBarActivity {
  Chronometer focus;
  Button start, stop, reset;
  long timeElapsed = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    start = (Button) findViewById(R.id.button1);       
    focus = (Chronometer) findViewById(R.id.chronometer1);
    // to get the elapsed time use setonChronometerTickListener
    focus.setOnChronometerTickListener(new OnChronometerTickListener() {
         @Override
         public void onChronometerTick(Chronometer chronometer) {
             timeElapsed = SystemClock.elapsedRealtime() - focus.getBase();
         }
    });
    start.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            if(timeElapsed == 0){
            focus.setBase(SystemClock.elapsedRealtime());
            focus.start();
            }

            if(timeElapsed != 0){
        timeElapsed = 0;
            focus.stop();    
            }
        }
    });

}

Upvotes: 1

Gotiasits
Gotiasits

Reputation: 1175

The problem with your code is this line:

long timeElapsed = SystemClock.elapsedRealtime() - focus.getBase();

Since focus variable has not been initialized you get NullPointer. You should call getBase() after initialization.

Also, you should use ToggleButton instead of Button for this App.

Upvotes: 1

Related Questions