estimateDirectionOfText method

TextDirection estimateDirectionOfText (String text, { bool isHtml: false })

Estimates the directionality of text using the best known general-purpose method (using relative word counts). A TextDirection.UNKNOWN return value indicates completely neutral input. isHtml is true if text HTML or HTML-escaped.

If the number of RTL words is above a certain percentage of the total number of strongly directional words, returns RTL. Otherwise, if any words are strongly or weakly LTR, returns LTR. Otherwise, returns UNKNOWN, which is used to mean neutral. Numbers and URLs are counted as weakly LTR.


static TextDirection estimateDirectionOfText(String text,
    {bool isHtml: false}) {
  text = isHtml ? stripHtmlIfNeeded(text) : text;
  var rtlCount = 0;
  var total = 0;
  var hasWeaklyLtr = false;
  // Split a string into 'words' for directionality estimation based on
  // relative word counts.
  for (String token in text.split(new RegExp(r'\s+'))) {
    if (startsWithRtl(token)) {
    } else if (new RegExp(r'^http://').hasMatch(token)) {
      // Checked if token looks like something that must always be LTR even in
      // RTL text, such as a URL.
      hasWeaklyLtr = true;
    } else if (hasAnyLtr(token)) {
    } else if (new RegExp(r'\d').hasMatch(token)) {
      // Checked if token contains any numerals.
      hasWeaklyLtr = true;

  if (total == 0) {
    return hasWeaklyLtr ? TextDirection.LTR : TextDirection.UNKNOWN;
  } else if (rtlCount > _RTL_DETECTION_THRESHOLD * total) {
    return TextDirection.RTL;
  } else {
    return TextDirection.LTR;