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    <p>That <code>NullPointerException</code> comes from the fact that you initialize your <code>Views</code> using the <code>getActivity()</code> method where you declare them as fields in the <code>F_NPV</code> class. The method <code>getActivity()</code> method will return a valid <code>Activity</code> reference after the callback <code>onAttach()</code> is called, so the way you initialize the views will not work as, at that moment(when the fields of the <code>Fragment</code> class are initialized) the method <code>getActivity</code> will return <code>null</code>, no valid reference. The correct way to do that initialization is doing it in the <code>onActivityCreated</code> callback:</p> <pre><code>EditText r; Button calc; //... @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); r = (EditText) getActivity().findViewById(R.id.npv_rate); calc = (Button) getActivity().findViewById(R.id.npv_calc); //... </code></pre> <p>Also, if I may, some suggestions regarding your code:</p> <p>You're doing some double's parsing from Strings and it may be a good idea to check the input so you don't throw a <code>NumberFormatException</code>. For example, if the user creates some <code>EditTexts</code> and then clicks the calculate <code>Button</code>(I know, it sounds silly, but there are chances the user will do it(I did it for example)), you'll throw a <code>NumberFormatException</code> as you try to parse an empty <code>String</code>. Instead make a little check:</p> <pre><code>public void onClick(View arg0) { Double r1 = Double.parseDouble((r.getText().toString()) .equals("") ? "0" : r.getText().toString()); EditText editText = (EditText) getActivity().findViewById(i); TextView answer = (TextView) getActivity().findViewById(R.id.npv_answer); double[] CashFlows; CashFlows = new double[i]; double result = 0; String tmp = editText.getText().toString(); CashFlows[i] = (Double.parseDouble(tmp.equals("") ? "0" : tmp)) / (Math.pow(1 + r1, i)); //... </code></pre> <p>Also, even if you have correct values in the <code>EditText</code> the above code will throw a <code>NullPointerException</code>, as the <code>editText</code> variable will be <code>null</code>. The reason for this is in the <code>while</code> loops that you used to create the fields. For example, if the user moves the <code>SeekBar</code> to 3 than the <code>while</code> loop will run 3 times, each time incrementing the <code>i</code> value. So <code>i</code> will be <code>0</code>, <code>1</code>, <code>2</code>, so far correct but because you increment <code>i</code> each time the final <code>i</code> will be <code>4</code>. Now in the <code>onClick</code> method you'll look for an <code>EditText</code> with the id <code>i</code>, but as there is no <code>EditText</code> in the layout with the id <code>4</code>, the view will be <code>null</code>. </p> <p>Also, try to give your classes better names, you may know very well what they mean but you could be making things worse for someone that reads your code(like F_PNV, F_PV etc).</p> <p>Code for the <code>onActivityCreated</code> method. This should solve what you're trying to do(if I understand what you want):</p> <pre><code>@Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); r = (EditText) getActivity().findViewById(R.id.npv_rate); calc = (Button) getActivity().findViewById(R.id.npv_calc); final LinearLayout linearLayout = (LinearLayout) getActivity() .findViewById(R.id.npv_calcfields); SeekBar bar = (SeekBar) getActivity().findViewById(R.id.npv_seekbar); final TextView selection = (TextView) getActivity().findViewById( R.id.npv_selected); bar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() { public void onProgressChanged(SeekBar seekbar, int progress, boolean fromUser) { selection .setText("You have selected " + progress + " periods."); if (progress == 0) { String normalstring = getActivity().getResources() .getString(R.string.npv1); selection.setText(normalstring); linearLayout.removeAllViews(); // the progress is 0 so // remove all the views that // are currently present } else { int currentChilds = linearLayout.getChildCount(); if (currentChilds &lt; progress) { while (currentChilds != progress) { EditText editText = new EditText(getActivity()); editText.setLayoutParams(new LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); linearLayout.addView(editText); currentChilds++; } } else if (currentChilds &gt; progress) { while (currentChilds != progress) { linearLayout.removeViewAt(linearLayout .getChildCount() - 1); currentChilds--; } } } } public void onStopTrackingTouch(SeekBar arg0) { } public void onStartTrackingTouch(SeekBar arg0) { } }); calc.setOnClickListener(new OnClickListener() { public void onClick(View view) { Double r1 = Double.parseDouble((r.getText().toString()) .equals("") ? "0" : r.getText().toString()); TextView answer = (TextView) getActivity().findViewById( R.id.npv_answer); final LinearLayout linearLayout = (LinearLayout) getActivity() .findViewById(R.id.npv_calcfields); int size = linearLayout.getChildCount(); double[] CashFlows = new double[size]; double result = 0; for (int i = 0; i &lt; size; i++) { EditText editText = (EditText) linearLayout.getChildAt(i); String tmp = editText.getText().toString(); CashFlows[i] = (Double.parseDouble(tmp.equals("") ? "0" : tmp)) / (Math.pow(1 + r1, i)); } for (double d : CashFlows) { result += d; } answer.setText("answer is " + result); } }); } </code></pre>
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    1. COthanks for the info, as for the while loop, my heart isnt attached to it but when i dont have it, there is a lag and most times when you slide down from 4 to 2 it will still have 3 fields left, the while loop fixed that. Also why will the final i be 4? i starts at 0 so incrementing it 3 times makes it 1,2,3 ? what if i initilaize it as -1? would that work? (not a int anymore then but w/e).
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    2. COAlso for the class names :) F_ denotes a fragment :) and the other things after are names of a financial mathematics term NPV is for example the short form for Net Present Value, PV = Present Value, = PVAnn = Present Value of Annuity
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    3. CO@Killerpixler You could put a log entry and see what is the value for `i` when you enter the `onClick` method ;). Generally, abbreviations like the ones you used are not very descriptive and you should avoid them. Anyway, I've edited my answer and added some code on how I would write the `onActivityCreated` method.
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