Create a list from a string extracted from another list with Kotlin

Question

In my application, I use this class as a model:

class ExpenseItem (val concept: String, val amount: String, val months: List<String>, val type: Type, val cards_image: Int, val payDay: Int, val notes: String) {

    enum class Type {RECURRENT, VARIABLE}
}

And with this model, I create a mutable list

var generalExpensesList: MutableList<ExpenseItem> = mutableListOf()

and I add items

 val currentExpense = ExpenseItem(
                    concept,
                    amount,
                    listOfMonths,
                    enumtype,
                    card_image_number,
                    payday.toInt(),
                    notes
                )

                generalExpensesList.add(currentExpense)

As you can see, one of the model fields is also a String type list, in case it was important

Well, my intention is to convert this list to String, save it as a sharedpreference, and then create a new list using that String retrieved from the sharedpreference. To convert the list to String I can use toString or joinToString, both give me an optimal result. I have the problem when I want to create a new list from the String. I can do it with lists of type List<String>, but never with lists of type List<ExpenseItem>

Can someone help me with this?

Using Gson map it to Json and save to SharePreference, and you can easy to retrieved List<ExpenseItem> — Công Hải
– Công Hải, Commented May 27, 2020 at 8:28
You mean the GSON library, right? I have never used it. I will have to investigate to see how it works. Would you know of any implementation example applied to this?. Thanks — Sergio76
– Sergio76, Commented May 27, 2020 at 8:32
For instance you have in you sharedPrefs [one, two]. Do you want to convert this content form String to List<String>? — Andrey Molochko
– Andrey Molochko, Commented May 27, 2020 at 8:34
no, the sharedprefs is a string with the data of the model class "ExpenseItem" and that String is what I want to convert to a list of type List<ExpenseItem> — Sergio76
– Sergio76, Commented May 27, 2020 at 8:37

Công Hải · Accepted Answer · 2020-05-27 08:38:41Z

2

Simple way, you can use Gson library, add it to build.gradle, it will serialize your list to JSON and save it to SharePreference

  implementation 'com.google.code.gson:gson:2.8.6'

    public void saveItems(List<ExpenseItem> items) {
        if (items != null && !items.isEmpty()) {
            String json = new Gson().toJson(items);
            mSharedPreferences.edit().putString("items", json).apply();
        }
    }

    public List<ExpenseItem> getItems() {
        String json = mSharedPreferences.getString("items", "");
        if (TextUtils.isEmpty(json)) return Collections.emptyList();
        Type type = new TypeToken<List<ExpenseItem>>() {
        }.getType();
        List<ExpenseItem> result = new Gson().fromJson(json, type);
        return result;
    }

answered May 27, 2020 at 8:38

Công Hải

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Comments

Dipak Sharma · Accepted Answer · 2020-05-27 08:41:35Z

1

You need to use Gson() class. First Make class like below

class WhateverName(var generalExpensesList: MutableList<ExpenseItem> = mutableListOf())

and pass your list to this class and make a object of this class and then need to make string of it like below

Gson().toJson(WhateverName(arrayListOf()))

it will give you the string and save it to preference as a string. After retrieve string from preference you need convert it to that object again for doing that use below code.

Gson().fromJson("string", WhateverName::class.java)

it will give you the class of WhateverName, you can access your list from it.

answered May 27, 2020 at 8:41

Dipak Sharma

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