subStringWithoutEmoji method

String subStringWithoutEmoji(
  1. int start, [
  2. int? end
])

截取字符串，但是不截断emoji表情 emoji表情占两个字符，high+low

Implementation

String subStringWithoutEmoji(int start, [int? end]) {
  var relStart = start;
  var relEnd = end ?? length;
  if (start != 0) {
    int c = this[start].codeUnitAt(0);
    // 如果是低位代理，则开始位置直接放弃表情
    if (isLowSurrogate(c)) {
      relStart++;
    }
  }
  if (end != null && end < length) {
    int c = this[end].codeUnitAt(0);
    // 如果是低位代理，则结束位置向后移动一位，包含表情
    if (isLowSurrogate(c)) {
      relEnd++;
    }
  }
  return substring(relStart, relEnd);
}