How to add a character in EditText after user starts typing

Question

I have an editText where a user inputs a phone number, but right when they click their first number, I want a \'+\' to appear in the beginning of the text. I have this code but

Answer 1

    Pattern p = Pattern.compile("^\\d+.*");

editText.addTextChangedListener(new TextWatcher() {

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count,
                                      int after) {
        }

        @Override
        public void afterTextChanged(Editable s) {
            if (p.matcher(s.toString().trim()).matches()) {
                editText.setText(prefix + s.toString());
            }
            Selection.setSelection(editText.getText(), editText.getText().length());
        }
    });