Flutter Save JSON Array to SharedPreferences

Question

How to save JSON array into SharedPreferences?

I've tried some code like this below, but i got some error :

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: type 'Text' is not a subtype of type 'String'

for (var x = 0; x < dynamicwidget.length - 1; x++) {
  _listOrder={
    "id_product": dataJSON[x]["product_id"],
    "order_count": dynamicwidget[x].controller.text,
  };
}

String json = jsonEncode(_listOrder);

SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setString(categoryname, json);

replace this dynamicwidget[x].controller.text with dynamicwidget[x].controller.text.toString() — primo
– primo, Commented May 6, 2019 at 6:35
instead of doing like this save order_count value in a variable and then assign it here — primo
– primo, Commented May 6, 2019 at 7:04

kounex · Accepted Answer · 2019-05-13 12:37:17Z

3

I would recommend you to use something like this (local storage implementation) which is made for saving and loading JSON.

From the code snippet itself i can't tell you exactly what is causing this exception but basically everywhere a String is beeing expected but you provided an actual Text widget. It could be the categoryname variable. What kind of controller do you get from your dynamicWidget instance? Are you sure controller.text returns a String?

Another note: you are re-assigning _listOrder with every for loop instead of adding information. You have to use an empty array which will be filled with every loop.

answered May 13, 2019 at 12:37

kounex

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3 Comments

izuddin Over a year ago

Noted, Thank for you reference

Kaigo Over a year ago

this library is legacy as it doesn't support null safety

kounex Over a year ago

As of version 4.0.0+1 it has been made null safe and can therefore be used as usual

izuddin · Accepted Answer · 2019-05-14 02:24:07Z

Thanks all, for contributing this question. I've solved this question and makes some change.

_listOrder.clear();
    for (var x = 0; x < dynamicwidget.length; x++) {
      int jml = int.parse(dynamicwidget[x].controller.text == ""? "0": dynamicwidget[x].controller.text);
      if (jml > 0) {
        _listOrder.add({
          "id_product": dataJSON[x]["product_id"],
          "order_count": dynamicwidget[x].controller.text,
        });
      }
    }

    if (_listOrder.length > 0) {
      SharedPreferences prefs = await SharedPreferences.getInstance();
      Map<String, dynamic> _collOrder = Map<String, dynamic>();
      String sessjson = prefs.getString("orderlist");
      if (sessjson != null) {
        _collOrder = json.decode(sessjson);
        _collOrder.remove(categoryname);
      }
      _collOrder[categoryname] = _listOrder;
      prefs.setString("orderlist", json.encode(_collOrder));
    }

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