How Can I Can I Fix the ImageView NullPointerException in My Android Game

I’m building a classic Pong style for Android game, and I wanted to implement a fun feature an image based score counter using ImageView and drawable resources. But something weird happened the game compiled and ran fine at first, but crashed every single time the ball reached the edge of the screen.

Here’s how I tracked down the issue, fixed it, and added even more functionality along the way.

The Problem: NullPointerException

When the ball hit the top or bottom edge, my app crashed with this error:

E/AndroidRuntime: FATAL EXCEPTION
java.lang.NullPointerException at com.Pong.GameState.update(GameState.java:154)

The code causing this was:

TopCounter.setImageResource(myImageList[i+1])

Clearly, TopCounter was null at this point but why

Understanding the Cause

I had this line in my game thread:

_state = new GameState();

But here’s the thing GameState was extending Activity, and by manually calling new GameState(), I completely bypassed Android’s lifecycle, meaning onCreate() (where I initialize views with findViewById()) was never called.

As a result, both TopCounter and BottomCounter remained null.

The Fix

I had two solid options, and I went with the cleanest one separating game logic from UI by turning GameState into a plain Java class (not an Activity) and using a listener callback to update the UI from my main activity.

Refactoring My GameState Class

First, I removed extends Activity from GameState and stripped out all UI logic. Then I added this callback interface:

public interface ScoreListener {
    void onTopScore(int score);
    void onBottomScore(int score);
}

In GameState, I held a reference to a listener:

private ScoreListener listener;

public void setScoreListener(ScoreListener l) {
    listener = l;
}

Then, inside the android game update logic, I notified the listener when a score changed:

if (_ballY > _screenHeight) {
    _toppoint++;
    if (listener != null) listener.onTopScore(_toppoint);
}

Now, in my Activity or GameView, I implemented the ScoreListener like this:

gameState.setScoreListener(new GameState.ScoreListener() {
    @Override
    public void onTopScore(int score) {
        TopCounter.setImageResource(myImageList[score]);
    }

    @Override
    public void onBottomScore(int score) {
        BottomCounter.setImageResource(myImageList[score]);
    }
});

No more NullPointerException, and my score updates as expected.

Adding More Game Feature

Once the scoring system worked, I added some fun and useful features:

Win Condition

When a player reaches 9 points:

if (_toppoint == 9 || _bottompoint == 9) {
    // Show "You Win!" or "You Lose!" message
    // Stop the game loop
}

Restart Button

I added a restart button in my layout and used a method like this to reset the game:

public void resetGame() {
    _ballX = _screenWidth / 2;
    _ballY = _screenHeight / 2;
    _toppoint = 0;
    _bottompoint = 0;
    if (listener != null) {
        listener.onTopScore(0);
        listener.onBottomScore(0);
    }
}

Sound Effects

I used SoundPool to add sounds for bouncing, scoring, and winning. It really brought the game to life!

Final Thought

Debugging this issue reminded me how tightly coupled logic and UI can cause subtle bugs, especially in Android. The key takeaway? Never instantiate an Activity manually, and always separate game logic from UI handling. By refactoring with a listener pattern, not only did I fix the crash, but I also made the code cleaner, easier to test, and more scalable.