How do I remove childview from parent layout before creating an alertdialog in android?

Question

I am trying to create an AlertDialog after cancelling the previous alert using ad.cancel() in my code.

private void make_changes() {
        if(new_spin != null){
            new_spin.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                @Override
                public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                    if(i != 0) {
                        ad.cancel();
                        builder.setMessage("Make your changes below:");
                        TextView book = new TextView(getContext());
                        TextView page = new TextView(getContext());
                        TextView type = new TextView(getContext());
                        TextView no = new TextView(getContext());

                        book.setPadding(70, 10, 10, 20);
                        book.setTypeface(null, Typeface.BOLD);
                        page.setPadding(70,10,10,20);
                        page.setTypeface(null,Typeface.BOLD);
                        type.setPadding(70,10,10,20);
                        type.setTypeface(null,Typeface.BOLD);
                        no.setPadding(70,10,10,50);
                        no.setTypeface(null,Typeface.BOLD);

                        EditText book_no = new EditText(getContext());
                        EditText page_no = new EditText(getContext());
                        EditText qtr_type = new EditText(getContext());
                        EditText qtrno = new EditText(getContext());

                        book_no.setPadding(70, 10, 10, 20);
                        page_no.setPadding(70,10,10,20);
                        qtr_type.setPadding(70,10,10,20);
                        qtrno.setPadding(70,10,10,50);

                        book.setText("Book");
                        page.setText("Page");
                        type.setText("Qtr type");
                        no.setText("Qtr No");

                        LinearLayout diagLayout = new LinearLayout(getContext());
                        diagLayout.setOrientation(LinearLayout.VERTICAL);

                        LinearLayout diagLayout1 = new LinearLayout(getContext());
                        diagLayout1.setOrientation(LinearLayout.HORIZONTAL);

                        for(int j=0; j<arr.size(); j++){
                            try {
                                if(arr.get(j).get(1).toString() == new_spin.getSelectedItem()){
                                    book_no.setText(arr.get(j).get(0).toString());
                                    page_no.setText(arr.get(j).get(1).toString());
                                    qtr_type.setText(arr.get(j).get(2).toString());
                                    qtrno.setText(arr.get(j).get(3).toString());
                                }
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }

                        diagLayout.addView(border1);
                        diagLayout1.addView(book);
                        diagLayout1.addView(book_no);
                        diagLayout1.addView(page);
                        diagLayout1.addView(page_no);
                        diagLayout1.addView(type);
                        diagLayout1.addView(qtr_type);
                        diagLayout1.addView(no);
                        diagLayout1.addView(qtrno);
                        diagLayout1.addView(border);
                        diagLayout.addView(diagLayout1);

                        builder.setView(diagLayout);

                        builder.setPositiveButton("Submit", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialogInterface, int i) {

                            }
                        });

                        builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialogInterface, int i) {
                                book_no.setText("");
                                page_no.setText("");
                                qtr_type.setText("");
                                qtrno.setText("");
                                dialogInterface.dismiss();
                            }
                        });
                    }
                }

                @Override
                public void onNothingSelected(AdapterView<?> adapterView) {

                }
            });
            ad = builder.create();
            ad.show();
        }
    }

---

When I execute the function above, I keep getting this error on ad.show():

The specified child already has a parent. You must call removeView() on the child's parent first.

Why is this and how do I fix it?