How to restrict TextView to allow only alpha-numeric characters in Android

Question

I have a TextView in my app that i want a user to be able to only enter alpha-numeric characters in. How can this be done? Thanks!

Answer 1

The InputFilter solution works well, and gives you full control to filter out input at a finer grain level than android:digits. The filter() method should return null if all characters are valid, or a CharSequence of only the valid characters if some characters are invalid. If multiple characters are copied and pasted in, and some are invalid, only the valid characters should be kept (@AchJ's solution will reject the entire paste if any characters a invalid).

public static class AlphaNumericInputFilter implements InputFilter {
    public CharSequence filter(CharSequence source, int start, int end,
            Spanned dest, int dstart, int dend) {

        // Only keep characters that are alphanumeric
        StringBuilder builder = new StringBuilder();
        for (int i = start; i < end; i++) {
            char c = source.charAt(i);
            if (Character.isLetterOrDigit(c)) {
                builder.append(c);
            }
        }

        // If all characters are valid, return null, otherwise only return the filtered characters
        boolean allCharactersValid = (builder.length() == end - start);
        return allCharactersValid ? null : builder.toString();
    }
}

Also, when setting your InputFilter, you must make sure not to overwrite other InputFilters set on your EditText; these could be set in XML, like android:maxLength. You must also consider the order that the InputFilters are set. When used in conjunction with a length filter, your custom filter should be inserted before the length filter, that way pasted text applies the custom filter before the length filter (@AchJ's solution will overwrite all other InputFilters and only apply the custom one).

    // Apply the filters to control the input (alphanumeric)
    ArrayList curInputFilters = new ArrayList(Arrays.asList(editText.getFilters()));
    curInputFilters.add(0, new AlphaNumericInputFilter());
    InputFilter[] newInputFilters = curInputFilters.toArray(new InputFilter[curInputFilters.size()]);
    editText.setFilters(newInputFilters);