redo method

Implementation

void redo() {
  if (_redoStack.isNotEmpty) {
    final nextState = _redoStack.removeLast();
    _undoStack.add(state.copyWith());

    emit(nextState.copyWith(
      canUndo: true,
      canRedo: _redoStack.isNotEmpty,
      status: DiagramStatus.ready,
    ));
  }
}