Creating widgets inside nested for loop

Question

I am not able to access the outer for loop counter in inner for loop

Any idea on how to do this ?

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

import 'package:flutter/material.dart'; class Categories { Categories( {@required this.categoryname, @required this.categoryImage, @required this.subcategory}); String categoryname; String categoryImage; List<dynamic> subcategory; Categories.fromMap(Map<dynamic, dynamic> map) { this.categoryname = map['name']; this.categoryImage = map['imageurl']; this.subcategory = map['subcategory']; } } — user3048099
– user3048099, Commented Jul 7, 2019 at 7:29

Gazihan Alankus · Accepted Answer · 2019-07-07 08:39:32Z

You don't have a nested loop here. Please see the comments I added below:

  children: <Widget>[
    // this creates scat.length many Text elements here
    for (int i = 0; i < scat.length; i++) Text(scat[i].categoryname),
    // there is only one column that comes after the scat.length many Text elements 
    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())
      ],
    )
  ],

Here's how you can create categories in a nested loop:

  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())
        ],
      )
    ]
  ],

Note that to add two elements in each loop iteration we had to put the two into a list and unwrap it with the ... spread operator.

Abbas.M · Accepted Answer · 2019-07-07 07:28:16Z

0

I don't think the syntax you're using is proper as you're trying to create a for loop inside a return statement. Instead you can try this:

  @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
    );
  }

answered Jul 7, 2019 at 7:28

Abbas.M

3,4243 gold badges15 silver badges24 bronze badges

2 Comments

Gazihan Alankus Over a year ago

It's a new Dart feature: medium.com/flutter-community/…

Abbas.M Over a year ago

Wow. Thanks for bringing this into my attention! Saw your answer looks neat. Will start using that myself!

Srini J V · Accepted Answer · 2022-10-18 13:16:15Z

0

 children: <Widget>[
// this creates scat.length many Text elements here
for (int i = 0; i < scat.length; i++) Text(scat[i].categoryname),
// there is only one column that comes after the scat.length many Text elements 
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())
  ],
)

],

answered Oct 18, 2022 at 13:16

Srini J V

11 bronze badge

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