How to return a list of sublists from a specific item with flutter?-CodePudding

Actually, I'm trying to return a list from the 19th index, but this didn't work for me. This list is split into sub lists. I want to start splitting it from the 19th index not from 0.

This is my code:

static Future<List> local() async {
    File textAsset = File('/storage/emulated/0/RPSApp/assets/bluetooth.txt');
    final text = await textAsset.readAsString();
    final bytes =
        text.split(',').map((s) => s.trim()).map((s) => int.parse(s)).toList();

    int chunkSize = 19;


    List<int> padTo(List<int> input, int count) {
      return [...input, ...List.filled(count - input.length, 255)];
    }

    List<int> padToChunksize(List<int> input) => padTo(input, chunkSize);
    List<List<int>> items;
    items = bytes.slices(chunkSize).map(padToChunksize).toList();
    for (int i = 19; i < bytes.length; i  ) {
      return items;
    }

    return items;
  }

this code is for displaying sublists one by one:

 final chun = await Utils.local();
 await Future.forEach(chun, (ch) async {

                  

                    await Future.delayed(const Duration(seconds: 4));
                    await c.write(chun, withoutResponse: true);
                    await c.read();
                    await Future.wait(getValue());
                  }
                })

I don't know what's wrong with this code and why it returns me the list from index 0.

CodePudding user response：

Honestly its quite difficult to understand your code. since its mixed in 1 function.

its return from index 0 because:

 items = bytes.slices(chunkSize).map(padToChunksize).toList();

and then you keep return items. which is return all items. you have to create new list and cut the index based on you need.

Solutions:

ill answer based on list that you provide in comment section:

List data = [144, 9, 146, 8, 191, 0, 32, 0, 240, 84, 130, 16, 70, 79, 240, 0, 11, 170, 0, 0, 0, 242];

// method 1 ( recomended) 
final newList = data.skip(19);
print(newList); // result: (0, 0, 242)

// method 2
final newlist2 = temp.getRange(19,data.length);
print(newlist2); // result: (0, 0, 242)

both method will return the list from index 19. choode which method do you like to use. i will recommend to use skip, since it will not throw error if the list length is less than 19

CodePudding user response：

If you look at the code snipper below, you are returning complete list of input and another set of list with filled with 255 which is wrong.

List<int> padTo(List<int> input, int count) {
   return [...input, ...List.filled(count - input.length, 255)];
 }

If you want to return the list from index 19, then you need to correct the code snippet as below.

List<int> padTo(List<int> input, int count) {
  return [...input.skip(19), ...List.filled(count - input.length, 255)];
 }

This will skip the first 19 elements in the input list, but you must understand that the input of length is more than 19 otherwise, it will return a empty list.