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pDiscount.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void afterTextChanged(Editable editable) {
                if (editable.toString().startsWith(".")){
                    pDiscount.setError("Can't start with "+editable.charAt(0));
                    pDiscount.setText("");
                }

            }
        });