Question

我正在尝试遍历用作游戏板的2D阵列。我需要遍历2D数组中的每个[x] [y]元素，然后查看其所有相邻单元格，并确定它们是否包含1或0。我正在制作John Conway Game of Life应用程序，需要确定有多少个“活动”（2D数组中的相邻单元格中包含1）。

当我使用嵌套的for循环迭代2D数组并尝试将当前单元格与其邻居进行比较时，遇到了未定义的错误。

for(let x = 0; x < this.state.boardHeight; x++) {
        for(let y = 0; y < this.state.boardWidth; y++) {
          let neighborCount = 0;
          // Game of Life logic pertaining to squares being alive/dead
          neighborCount += oldBoard[x - 1][y - 1];
          neighborCount += oldBoard[x][y - 1];
          neighborCount += oldBoard[x + 1][y - 1];
          neighborCount += oldBoard[x - 1][y];
          neighborCount += oldBoard[x + 1][y];
          neighborCount += oldBoard[x - 1][y + 1];
          neighborCount += oldBoard[x][y + 1];
          neighborCount += oldBoard[x + 1][y + 1];

          console.log('neighborCount ' + neighborCount[x]);

          // If square has 2 live neighbors it stays alive
          if(neighborCount == 2) {
            newBoard[x][y] = oldBoard[x][y];
          }
          // If square has exactly 3 neighbors a new life square is born
          else if (neighborCount == 3) {
            newBoard[x][y] = 1;
          }
          // Is square has more than 3 live neighbors it dies
          else if(neighborCount > 3){
            newBoard[x][y] = 0;
          }
        }
       }

所有neighborCount += oldBoard[x][y]行代码均未定义返回。我如何迭代和比较有什么问题？

Cannot read property '-1' of undefined
App._this.componentDidUpdate
/src/App.js:93:43
  90 | for(let y = 0; y < this.state.boardWidth; y++) {
  91 |   let neighborCount = 0;
  92 |   // Game of Life logic pertaining to squares being alive/dead
> 93 |   neighborCount += oldBoard[x - 1][y - 1];
     |                                   ^
  94 |   neighborCount += oldBoard[x][y - 1];
  95 |   neighborCount += oldBoard[x + 1][y - 1];
  96 |   neighborCount += oldBoard[x - 1][y];

这就是我得到的错误。 Here is a Codesandbox和整个程序。

Answer 1

答案在您的错误消息中：Cannot read property '-1' of undefined

您的代码从x = 0, y = 0开始，然后第一行尝试访问oldBoard[x - 1][y - 1]，那么这意味着什么呢？

答案：oldBoard[0 - 1][0 - 1]，即oldBoard[-1][-1]

oldBoard[-1]的值为undefined，因此它实际上是在尝试做undefined[-1]，但是undefined没有名为-1的属性，因此它抛出错误。

您需要以不尝试查看无效单元格的方式编写代码。

反应-遍历2d数组并将当前元素与相邻元素及其值进行比较

1 个答案: