// Step 1: designate a style
AwesomeValidation mAwesomeValidation = new AwesomeValidation(BASIC);
// or
AwesomeValidation mAwesomeValidation = new AwesomeValidation(COLORATION);
mAwesomeValidation.setColor(Color.YELLOW);  // optional, default color is RED if not set
// or
AwesomeValidation mAwesomeValidation = new AwesomeValidation(UNDERLABEL);
mAwesomeValidation.setContext(this);  // mandatory for UNDERLABEL style
// setUnderlabelColor is optional for UNDERLABEL style, by default it's holo_red_light
mAwesomeValidation.setUnderlabelColorByResource(android.R.color.holo_orange_light); // optional for UNDERLABEL style
mAwesomeValidation.setUnderlabelColor(ContextCompat.getColor(this, android.R.color.holo_orange_dark)); // optional for UNDERLABEL style
// or
AwesomeValidation mAwesomeValidation = new AwesomeValidation(TEXT_INPUT_LAYOUT);
// by default, it automatically sets focus to the first failed input field after validation is triggered
// you can disable this behavior by
AwesomeValidation.disableAutoFocusOnFirstFailure();

// Step 2: add validations
// support regex string, java.util.regex.Pattern and Guava#Range
// you can pass resource or string
mAwesomeValidation.addValidation(activity, R.id.edt_name, "[a-zA-Z\\s]+", R.string.err_name);
mAwesomeValidation.addValidation(activity, R.id.edt_tel, RegexTemplate.TELEPHONE, R.string.err_tel);
mAwesomeValidation.addValidation(activity, R.id.edt_email, android.util.Patterns.EMAIL_ADDRESS, R.string.err_email);
mAwesomeValidation.addValidation(activity, R.id.edt_year, Range.closed(1900, Calendar.getInstance().get(Calendar.YEAR)), R.string.err_year);
mAwesomeValidation.addValidation(activity, R.id.edt_height, Range.closed(0.0f, 2.72f), R.string.err_height);
// or
mAwesomeValidation.addValidation(editText, "regex", "Error info");

// to validate TextInputLayout, pass the TextInputLayout, not the embedded EditText
AwesomeValidation mAwesomeValidation = new AwesomeValidation(TEXT_INPUT_LAYOUT);
mAwesomeValidation.addValidation(activity, R.id.til_email, Patterns.EMAIL_ADDRESS, R.string.err_email);

// to validate the confirmation of another field
String regexPassword = "(?=.*[a-z])(?=.*[A-Z])(?=.*[\\d])(?=.*[~`!@#\\$%\\^&\\*\\(\\)\\-_\\+=\\{\\}\\[\\]\\|\\;:\"<>,./\\?]).{8,}";
mAwesomeValidation.addValidation(activity, R.id.edt_password, regexPassword, R.string.err_password);
// to validate a confirmation field (don't validate any rule other than confirmation on confirmation field)
mAwesomeValidation.addValidation(activity, R.id.edt_password_confirmation, R.id.edt_password, R.string.err_password_confirmation);

// to validate with a simple custom validator function
mAwesomeValidation.addValidation(activity, R.id.edt_birthday, new SimpleCustomValidation() {
    @Override
    public boolean compare(String input) {
        // check if the age is >= 18
        try {
            Calendar calendarBirthday = Calendar.getInstance();
            Calendar calendarToday = Calendar.getInstance();
            calendarBirthday.setTime(new SimpleDateFormat("dd/MM/yyyy", Locale.US).parse(input));
            int yearOfToday = calendarToday.get(Calendar.YEAR);
            int yearOfBirthday = calendarBirthday.get(Calendar.YEAR);
            if (yearOfToday - yearOfBirthday > 18) {
                return true;
            } else if (yearOfToday - yearOfBirthday == 18) {
                int monthOfToday = calendarToday.get(Calendar.MONTH);
                int monthOfBirthday = calendarBirthday.get(Calendar.MONTH);
                if (monthOfToday > monthOfBirthday) {
                    return true;
                } else if (monthOfToday == monthOfBirthday) {
                    if (calendarToday.get(Calendar.DAY_OF_MONTH) >= calendarBirthday.get(Calendar.DAY_OF_MONTH)) {
                        return true;
                    }
                }
            }
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return false;
    }
}, R.string.err_birth);

// to validate with your own custom validator function, warn and clear the warning with your way
mAwesomeValidation.addValidation(activity, R.id.spinner_tech_stacks, new CustomValidation() {
    @Override
    public boolean compare(ValidationHolder validationHolder) {
        if (((Spinner) validationHolder.getView()).getSelectedItem().toString().equals("< Please select one >")) {
            return false;
        } else {
            return true;
        }
    }
}, new CustomValidationCallback() {
    @Override
    public void execute(ValidationHolder validationHolder) {
        TextView textViewError = (TextView) ((Spinner) validationHolder.getView()).getSelectedView();
        textViewError.setError(validationHolder.getErrMsg());
        textViewError.setTextColor(Color.RED);
    }
}, new CustomErrorReset() {
    @Override
    public void reset(ValidationHolder validationHolder) {
        TextView textViewError = (TextView) ((Spinner) validationHolder.getView()).getSelectedView();
        textViewError.setError(null);
        textViewError.setTextColor(Color.BLACK);
    }
}, R.string.err_tech_stacks);

// Step 3: set a trigger
findViewById(R.id.btn_done).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mAwesomeValidation.validate();
    }
});

// Optional: remove validation failure information
findViewById(R.id.btn_clr).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mAwesomeValidation.clear();
    }
});