Input filter for edit text which filters both letter or digits or one of these.

CustomFilter.java

//todo handle cases when it erases whole text on newer android versions    
public class CustomFilter implements InputFilter {
        private boolean allowCharacter;
        private boolean allowDigits;
        

        public CustomFilter(boolean allowCharacter, boolean allowDigits) {
            this.allowCharacter = allowCharacter;
            this.allowDigits = allowDigits;
        }

        public void setAllowCharacter(boolean allowCharacter) {
            this.allowCharacter = allowCharacter;
        }

        public void setAllowDigits(boolean allowDigits) {
            this.allowDigits = allowDigits;
        }

        @Override
        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
            boolean valid = true;
            for (int i = start; i < end; i++) {
                char c = source.charAt(i);

                if (allowCharacter && allowDigits) {
                    if (!(Character.isLetter(c) || Character.isDigit(c))) {
                        valid = false;
                        break;
                    }
                } else if (allowCharacter && !Character.isLetter(c)) {
                    valid = false;
                    break;
                } else if (allowDigits && !Character.isDigit(c)) {
                    valid = false;
                    break;
                }
            }

            if (!valid) {
                return "";
            }

            return null;
        }
    }