Null pointer exception when using multiple fragment that uses a custom seek bar

Question

I have a custom Seek bar that that i made following a tutorial on the net. Here is the code for the CustomSeekBar class.

    public class CustomSeekBar extends SeekBar {

    private ArrayList<ProgressItem> mProgressItemsList;

    public CustomSeekBar(Context context) {
        super(context);
    }

    public CustomSeekBar(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomSeekBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void initData(ArrayList<ProgressItem> progressItemsList) {
        this.mProgressItemsList = progressItemsList;
    }

    @Override
    protected synchronized void onMeasure(int widthMeasureSpec,
                                          int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    protected void onDraw(Canvas canvas) {
        if (mProgressItemsList.size() > 0) {
            int progressBarWidth = getWidth();
            int progressBarHeight = getHeight();
            int thumboffset = getThumbOffset();
            int lastProgressX = 0;
            int progressItemWidth, progressItemRight;
            for (int i = 0; i < mProgressItemsList.size(); i++) {
                ProgressItem progressItem = mProgressItemsList.get(i);
                Paint progressPaint = new Paint();
                progressPaint.setColor(getResources().getColor(
                        progressItem.color));

                progressItemWidth = (int) (progressItem.progressItemPercentage
                        * progressBarWidth / 100);

                progressItemRight = lastProgressX + progressItemWidth;

                // for last item give right to progress item to the width
                if (i == mProgressItemsList.size() - 1
                        && progressItemRight != progressBarWidth) {
                    progressItemRight = progressBarWidth;
                }
                Rect progressRect = new Rect();
                progressRect.set(lastProgressX, thumboffset / 2,
                        progressItemRight, progressBarHeight - thumboffset / 2);
                canvas.drawRect(progressRect, progressPaint);
                lastProgressX = progressItemRight;
            }
            super.onDraw(canvas);
        }

    }
}

I have used this custom widget in a fragment. This fragment has multiple instance of this custom widget.

The fragment is used in multiple activities. There is an activity where the fragment works fine but in another activity where i try to use two of the above fragments i get a NullPointer Exception.

From the stacktrace i can trace the null pointer exception back to the line

if (mProgressItemsList.size() > 0) {

The strange thing is that when i add the fragment to only one framelayout the code works fine. But when i add the fragment to another framelayout in the same activity i get this null pointer exception. I am confused on what is causing this and am wondering what is the best way to tackle this?

Answer 1

The problem was that i was working with the view in the views of my fragment onActivityCreated() method. If you are planning to use the same fragment twice in any activity this is a very bad idea. I had two fragments initialized but only a single fragment and its views was initialized because i was using getActivity().findViewById() .

The solution to this is to work with your fragment's view on onViewCreated(View view, @Nullable Bundle savedInstanceState) and instead of using getActivity().findViewById() using view.findViewById().