问如何在dart中访问循环外的变量？

EN

void computerMove() {
    int _currentMove;
    int _currentScore = 0;
    int _bestMove; // here i initialize it
    int _bestScore = 0;
    List<String> boardWithMove = List.from(_board);
    if (!isWin() && !isDraw()) {
      for (int i = 0; i <= 8; i++) {
        // checks all first move possibilities
        if (_board[i] == null) {
          if (_computerIsX) {
            boardWithMove[i] = 'X';
            _currentMove = i;
            print(_currentMove);
            print('computer thinking');
          }
          // Try's all possibilities for the initial move
          for (int i = 0; i <= 8; i++) {
            if (boardWithMove[i] == null) {
              if (_computerTurn && _computerIsX) {
                boardWithMove[i] = 'X';
                _computerTurn = false;
                if (isWin()) {
                  _currentScore++;
                }
              } else if (!_computerTurn && _computerIsX) {
                boardWithMove[i] = 'O';
                _computerTurn = true;
                if (isWin()) {
                  _currentScore--;
                }
              }
            }
          }
          // safes the best move with best results
          if (_currentScore > _bestScore) {
            _bestScore = _currentScore;
            _bestMove = _currentMove; // here i change it
            print(_bestMove);
          }
        }
      }
      // sets the best output
      if (_computerIsX) {
        print(_bestMove); // returns null
        _board[_bestMove] = 'X'; // here I want to use it
      } else if (!_computerIsX) {
        _board[_bestMove] = 'O';
      }
    }
  }