DecimalDigitsInputFilter.java

    public class DecimalDigitsInputFilter implements InputFilter {
        private static String separators = "[\\.\\,]";

        private final Pattern mPattern;

        public DecimalDigitsInputFilter(int digitsBeforeSeparator, int digitsAfterSeparator) {
            String b = "(-?\\d{1," + digitsBeforeSeparator + "})";
            String a = "(\\d{1," + digitsAfterSeparator + "})";
            String s = separators;

            String numberRegex = new StringBuilder()
                    .append("(-)")
                    .append("|")
                    .append("(" + b + s + a + ")")
                    .append("|")
                    .append("(" + b + s +")")
                    .append("|")
                    .append("(" + b + ")")
                    .toString();

            mPattern = Pattern.compile(numberRegex);
        }

        @Override
        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
            String input = dest.toString().substring(0, dstart) + source.
                    subSequence(start, end) + dest.toString().substring(dend);

            Matcher matcher = mPattern.matcher(input);

            if (!matcher.matches()) {
                return "";
            }

            return null;
        }
    }

It's worked like a charm, thank you! I have a question: How can i achieve that comma (",") displayed on the screen not dot (".") because in Hungary we using comma as decimal separator.

android:digits="0123456789," setting can be add to the EditText. Moreover, instead of returning null in the DecimalDigitsInputFilter, you can return source.replace(".", ",")

according to the answer https://stackoverflow.com/a/40020731/1510222 there is no way to hide dot in a standard keyboard

Thank you for your great code and your help! Meanwhile i understand your code (i'm very newby in java & android) and i used the same solution what you wrote (...because it's trivial but not first sight for me :) )