Question

I get a null pointer exception and the program crash on each time I want to update the highscore text using setText(). what causes this problem?
this code is when i set my layout, the layout is a part of the gameView using opengl, and I put the highscore textview on the upper left corner

public void onCreate(Bundle savedInstanceState) {
    SFEngine.display = ((WindowManager)getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();//ambl ukuran width height layar
    super.onCreate(savedInstanceState);
    gameView = new SFGameView(this);
    gameView.setLayoutParams(new RelativeLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));

    RelativeLayout layout = new RelativeLayout(this);
    layout.setLayoutParams(new FrameLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));


    TextView textBox = new TextView(this);
    textBox.setId(1);
    textBox.setText("HIGH SCORE");
    textBox.setBackgroundColor(Color.BLUE);
    textBox.setWidth(SFEngine.display.getWidth()/2);
    textBox.setHeight(50);
    Button pauseButton = new Button(this);
    pauseButton.setText("PAUSE");
    pauseButton.setHeight(50);
    pauseButton.setWidth(SFEngine.display.getWidth()/2);
    pauseButton.setOnTouchListener(new OnTouchListener(){
        public boolean onTouch(View v, MotionEvent e) {
            //pause game
            SFEngine.isPlaying = false;
            Intent i1 = new Intent(SFGames.this, pause.class);
            gameView.onPause();
            startActivityForResult(i1,0);//hrs pk result soalny mw blk lg
            return true;
        }
    });


    RelativeLayout.LayoutParams lp_pause = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);

    RelativeLayout.LayoutParams lp_hs = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);

    lp_hs.addRule(RelativeLayout.ALIGN_PARENT_LEFT);

    lp_pause.addRule(RelativeLayout.ALIGN_PARENT_TOP);
    lp_pause.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);

    textBox.setLayoutParams(lp_hs);
    pauseButton.setLayoutParams(lp_pause);

    layout.addView(gameView);
    layout.addView(textBox);        
    layout.addView(pauseButton);
    setContentView(layout);

and here is the setText code

public boolean onTouchEvent (MotionEvent event){//buat nerima input user
    if(!SFEngine.isPlaying){
        finish();
    }
    textBox.setText("High Score :" + SFEngine.score);//here is the source of the prob
.....

error log:

 10-13 22:38:34.207: E/AndroidRuntime(528): FATAL EXCEPTION: main
10-13 22:38:34.207: E/AndroidRuntime(528): java.lang.NullPointerException
10-13 22:38:34.207: E/AndroidRuntime(528):  at com.starfighter.SFGames.onTouchEvent(SFGames.java:136)
10-13 22:38:34.207: E/AndroidRuntime(528):  at  android.app.Activity.dispatchTouchEvent(Activity.java:2367)

UPDATE :
i’ve updated the source code so the textview declaration is outside of the onCreate, it seems to be working normally now..

Answer 1

You should define the text view as a class field in the activity, outside the onCreate:

TextView textBox;

public void onCreate(Bundle savedInstanceState) {
    ....
    textBox = new TextView(this);
}