Question

我无法访问内部for循环中的外部for循环计数器

关于如何执行此操作的任何想法？

class buildsubcategories extends StatelessWidget {
  List<cate.Categories> scat;

  buildsubcategories(this.scat);
  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        for (int i = 0; i < scat.length; i++) Text(scat[i].categoryname),
        Column(
          children: <Widget>[
            for (int j = 0; j < scat.length; j++)
              Text(scat[i].subcategory[j]['subcategoryname'].toString())
          ],
        )
      ],
    );
  }
```}


Expected Result : Able to access the variable i in the inner for loop

Answer 1

您在这里没有嵌套循环。请查看我在下面添加的评论：

  children: <Widget>[
    // note the ... spread operator that enables us to add two elements 
    for (int i = 0; i < scat.length; i++) ...[ 
      Text(scat[i].categoryname),
      Column(
        children: <Widget>[
          // this creates scat.length many elements inside the Column
          for (int j = 0; j < scat.length; j++)
            Text(scat[i].subcategory[j]['subcategoryname'].toString())
        ],
      )
    ]
  ],

以下是在嵌套循环中创建类别的方法：

...

请注意，要在每个循环迭代中添加两个元素，我们必须将两个元素放入列表中，并使用public async Task<IActionResult> LoginConfirm(LoginViewModel model) { ApplicationUser user = await userManager.FindByNameAsync(model.Email); if (user!=null) { var status = await signInManager.PasswordSignInAsync(user, model.Pass,model.RememberMe,true); if (status.Succeeded) { TempData["msg"] = "You Login successful "; return RedirectToAction("Index","Home"); } } TempData["msg"] = "Somethings Wrong!"; return View("Login"); }扩展运算符对其进行解包。

Answer 2

当您试图在return语句中创建for循环时，我认为您使用的语法不合适。相反，您可以尝试以下方法：

  @override
  Widget build(BuildContext context) {
    List<Widget> myList = List.generate(10, (index){
      var outerText = [Text("OuterText")];
      return Column(
        children: outerText..addAll(List.generate(10, (index){
          Text("Inner Text");
        })),
      );
    });
    return Column(
      children: myList
    );
  }

在嵌套的for循环内创建小部件

2 个答案: