Noob - How to manipulate List arrays in Flutter-CodePudding

I'm very new to Flutter and I'll be grateful for any help. I've created a two dimensional List using List.generate and then I want to iterate through the List and change the first value in each row. I've done this in Dartpad and it works as expected. I cant get it to work in my Flutter app.

Here's the code that works in Dartpad:

List myList = List.generate(12, (i) => List<String>.filled(12, '-'), growable: false);

for (int i = 0; i < myList.length; i  ) {
  int s = i   1;
  myList[i][0] = "List $s";
}

But when I use it in Flutter as follows:

class _MyPage extends State<MyPage> {
  
  List myList =
      List.generate(12, (i) => List<String>.filled(12, '-'), growable: false);
  
    for (int i = 0; i < myList.length; i  ) {
      int s = i   1;
      myList[i][0] = "List $s";
    }

Flutter errors on the **for **loop stating:

Expected a class member.
Try placing this code inside a class member.

Removing the for loop leave the initial generated list, myList filled with '-' but I want to change the first item in each row to 'List x' by using a for loop.

For the life of me I cant sort this out. Please help.

CodePudding user response：

You can declare in a class only members that belong to it like variables, methods, getters...

adding directly a for loop is wrong and can't be accepted, however, in the other hand you can declare a function that executes the for loop code, like this:

class _MyPage extends State<MyPage> {

List myList =
  List.generate(12, (i) => List<String>.filled(12, '-'), growable: false);

executeLoop() {
 for (int i = 0; i < myList.length; i  ) {
  int s = i   1;
  myList[i][0] = "List $s";
}
}

now we have a class member which is the executeLoop, and now you can call that function to execute it.

the StateFulWidget have a lifecycle method called initState(), which is called automatically when the widget is added to the tree widget, so you can do like this:

  class _MyPage extends State<MyPage> {
List myList =List.generate(12, (i) => List<String>.filled(12, '-'), growable: false);
  


executeLoop() {
 for (int i = 0; i < myList.length; i  ) {
  int s = i   1;
  myList[i][0] = "List $s";
}

@override
 initState() {
 super.initState();
 executeLoop();
}
}

and now the executeLoop will be executed, which means that your for loop will be executed now as you expect.

Hope this helps you!