How to calcul a sum of string list in flutter?

Question

I use texfield to add number. After this I save in sharepreference the value in List

I search to make an addition of each value saved in this List

I tried this, but it doesn't works.

  load_list()async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {

      stringList = prefs.getStringList("list");


     sum = stringList.reduce((value, element) => value + element);

    });

  }

Igor Kharakhordin · Accepted Answer · 2019-11-26 11:40:59Z

5

reduce returns the same type as the type in the collection, so you should use fold instead.

final List<String> stringList = prefs.getStringList("list") ?? [];
final int sum = stringList.fold<int>(0, (prev, value) => prev + int.parse(value));

To make it completely null-safe:

final int sum = stringList.fold<int>(0, (prev, value) => prev + (int.tryParse(value ?? '0') ?? 0));

edited Nov 26, 2019 at 11:40

answered Nov 26, 2019 at 11:27

Igor Kharakhordin

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3 Comments

danypata Over a year ago

Just for safety I would do int.tryParse(value) ?? 0

danypata Over a year ago

There's no need for value ?? '0' inside the tryParse

Igor Kharakhordin Over a year ago

@danypata if you're sure in your data, yes. But if you pass null to int.tryParse it will throw an exception, be careful.

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