AttributedText constructor

AttributedText([ String? text, AttributedSpans? spans, Map<int, Object>? placeholders ])

Constructs an AttributedText whose content is comprised by a combination of text and placeholders, covered by the given attributed spans.

placeholders is a map from character indices to desired placeholder objects. The character indices in placeholders refer to the final indices when the placeholders have been combined with the text.

Example:

• Full text: "�Hello � World!�"
• text: "Hello World!"
• placeholders:
  • 0: MyPlaceholder
  • 7: MyPlaceholder
  • 15: MyPlaceholder

Notice in the example above that the final placeholder index is greater than the total length of the text String.

Implementation

AttributedText([
  String? text,
  AttributedSpans? spans,
  Map<int, Object>? placeholders,
])  : _text = text ?? "",
      spans = spans ?? AttributedSpans(),
      placeholders = placeholders ?? <int, Object>{} {
  assert(() {
    // ^ Run this in an assert with a callback so that the validation doesn't run in
    //   production and cost processor cycles.
    _validatePlaceholderIndices();
    return true;
  }());

  if (this.placeholders.isEmpty) {
    // There aren't any placeholders, so text with placeholders is the same as
    // text without placeholders.
    _textWithPlaceholders = _text;
  } else {
    // Create a 2nd plain text representation that includes stand-in characters
    // for placeholders.
    final buffer = StringBuffer();
    int start = 0;
    int insertedPlaceholders = 0;
    for (final entry in this.placeholders.entries) {
      final textSegment = _text.substring(start - insertedPlaceholders, entry.key - insertedPlaceholders);
      buffer.write(textSegment);
      start += textSegment.length;

      buffer.write(placeholderCharacter);
      start += 1;

      insertedPlaceholders += 1;
    }
    if (start - insertedPlaceholders < _text.length) {
      buffer.write(_text.substring(start - insertedPlaceholders, _text.length));
    }

    _textWithPlaceholders = buffer.toString();
  }
}