展开循环有效，for循环无效[重复]

Question

我有一些我不理解的行为。虽然展开的循环工作正常！！！循环抛出 IndexOutOfRangeExceptions。调试显示有 0..9 个团队按钮和 0..9 个卡片 c[i]。 :(

private void Awake()
{
    InitCards();
    // This works!
    teamButtons[0].onClick.AddListener(() => SetCard(c[0]));
    teamButtons[1].onClick.AddListener(() => SetCard(c[1]));
    teamButtons[2].onClick.AddListener(() => SetCard(c[2]));

    teamButtons[3].onClick.AddListener(() => SetCard(c[3]));
    teamButtons[4].onClick.AddListener(() => SetCard(c[4]));
    teamButtons[5].onClick.AddListener(() => SetCard(c[5]));

    teamButtons[6].onClick.AddListener(() => SetCard(c[6]));
    teamButtons[7].onClick.AddListener(() => SetCard(c[7]));
    teamButtons[8].onClick.AddListener(() => SetCard(c[8]));
    // This yields an IndexOutOfRangeException
    for (int i = 0; i < 9; ++i)
    {
      teamButtons[i].onClick.AddListener(() => { SetCard(c[i]); });
    } 
}

Answer 1

您正在 lambda 表达式中捕获 变量 i。执行该 lambda 表达式时，它将使用 i 的“当前”值 - 始终为 9。您想要捕获变量的 副本...您可以这样做在循环中引入一个新变量：

for (int i = 0; i < teamButtons.Length; i++)
{
    int index = i;
    teamButtons[i].onClick.AddListener(() => SetCard(c[index]));
}