How to save an Array List/Mutable List to SharedPreferences in Kotlin Android using Gson?

Question

I simply want to store my mutable list/array list of Strings to SharedPreferences in order to retrieve the saved list again after re-opening the app (USING GSON).

!! WITHOUT using any class. It's a simple mutable list (I add things with usedCodesList.add("example")):

private var usedCodesList = mutableListOf<String>("022", "027")

I did not find any tutorial that fits what I need. (NO Class, NO Recycler View or List View or anything like that. I use usedCodesList.add(), usedCodesList.clear() and the Gson library ONLY)

Can someone help me? Any help is GREATLY appreciated!! I'm a beginner and almost dying

If the list is not going to have duplicates, I believe SP have option to save StringSet. — TheLibrarian
– TheLibrarian, Commented Oct 20, 2022 at 19:24
Okay. the list won't have duplicates. I heard StringSet before in the 2983 tutorials I watched. Can you explain it or link me a video? How do I do it? — MautendoSkill
– MautendoSkill, Commented Oct 20, 2022 at 19:26
A good practice is to share codes if possible, it is easy to reproduce problems. — kallis
– kallis, Commented Oct 20, 2022 at 19:57
Also sharing the code via images is often frowned upon, when someone is trying to help you, making them have to type the code is gonna make them very unlikely to help. (This case is fine, so far). Can you post more of the code? (Using the code formatting :-)) — TheLibrarian
– TheLibrarian, Commented Oct 20, 2022 at 20:33

TheLibrarian · Accepted Answer · 2022-10-20 19:57:36Z

2

It's pretty straightforward, just like any other type.

val editor = sharedPreferences.edit()
editor.putStringSet("my_list", usedCodesList.toSet())
editor.apply() // Note that editor should be used as atomical operation, not have it open all the time.

and

usedCodesList = sharedPrefences.getStringSet("my_list", emptySet())?.toMutableList() ?: mutableListOf()

edited Oct 20, 2022 at 19:57

answered Oct 20, 2022 at 19:32

TheLibrarian

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5 Comments

MautendoSkill Over a year ago

Oh my god, thank you, no errors!! I will try it out right now and update you!!

MautendoSkill Over a year ago

Okay, the app is running but there's a problem: I made the usedCodesList visible by setting a TextView. The TextView shows: "[]"... And my function to check if a code is in the list doesn't work now. Is the new, retrieved list null or something? And is the new retrieved list again like a mutable list (it should be right?) so can I access the codes like this: for (s in usedCodesList) { ?

MautendoSkill Over a year ago

Okay, sure. Well there are 2 Strings initially set in the list: "022" and "027". After pressing on my "Load List" button the list should appear. I wrote it like that:

for (s in usedCodesList) {              freeDrinkVoucherCaption.text = freeDrinkVoucherCaption.text.toString() + s.toString()          }

MautendoSkill Over a year ago

Image updated!.

TheLibrarian Over a year ago

@MautendoSkill I am so sorry to bother you, but those too. It's maily for clarity if someone else would stumble on this question :-).

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