subStringWithMaxLength method

String subStringWithMaxLength(int maxLen, { int startLen = 2, int endLen = 2, String ellipsis = '...', })

根据最大字符限制截取字符串 例：xx...xx emoji表情按一个字符算，不截取

Implementation

String subStringWithMaxLength(int maxLen,
    {int startLen = 2, int endLen = 2, String ellipsis = '...'}) {
  if (length <= maxLen) {
    return this;
  }
  int firstIndex = startLen;
  if (startLen <= 0) {
    firstIndex = 0;
  } else {
    int startChar = this[firstIndex].codeUnitAt(0);
    if (isLowSurrogate(startChar)) {
      firstIndex++;
    }
  }
  int lastIndex = length - endLen;
  if (endLen <= 0 || lastIndex < 0) {
    lastIndex = length - 1;
  } else {
    int endChar = this[lastIndex].codeUnitAt(0);
    if (isLowSurrogate(endChar)) {
      lastIndex--;
    }
  }
  if (lastIndex <= firstIndex) {
    return this;
  }
  return substring(0, firstIndex) + ellipsis + substring(lastIndex);
}