Question

I am new to android/java so please bear with me. My code was working fine earlier, but ever since I added the for() loops, I have been getting a NullPointerException. Any Ideas?

public class PreferencesActivity extends Activity {

SharedPreferences settings;
SharedPreferences.Editor editor;
static CheckBox box, box2;

private final static CheckBox[] boxes={box, box2};
private final static String[] checkValues={"checked1", "checked2"};


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    box=(CheckBox)findViewById(R.id.checkBox);
    box2=(CheckBox)findViewById(R.id.checkBox2);

    settings= getSharedPreferences("MyBoxes", 0);
    editor = settings.edit();

    if(settings != null){

    for(int i =0;i<boxes.length; i++)
        boxes[i].setChecked(settings.getBoolean(checkValues[i], false));   
    }

}

@Override
protected void onStop(){
   super.onStop();

   for(int i = 0; i <boxes.length; i++){           
   boolean checkBoxValue = boxes[i].isChecked();        
   editor.putBoolean(checkValues[i], checkBoxValue);
   editor.commit();       
   }

    }
}

Answer 1

You initialise the values of box and box2 to be null (as this is the default value when they are not assigned explicitly). These values are then used when creating your Checkbox array boxes. Thus, boxes has two null values. You then reassign the values of box and box2. Note that this has no effect on the values within the boxes array. Thus when you attempt to access the values within the array you get a NullPointerException.

Set the values within boxes after you have assigned values for box and box2.