Flutter useful class for shared preferences

In the article shared preferences in depth, I explained how to use shared preferences in Flutter. In this article I want to show you a class that I designed to simplify its use. I created this class out of the need to store user data. For example, I used it in Send to Kindle to store a mail list. I also used it to store the user’s token list and to purchase data.

Overall, this structure can be used where there is the need of working with a list of strings. In my previous article, I have already shown how to store a list of strings in local cache. This class, however, makes it even easier to use and adds methods that allow us to work faster.

First, I created the method to save a local cache list as follows:

class CashedUserData {
  static Future<void> _writes = Future.value();
//add list by key reference in local cache  
static Future<void> addlist(String kPrefKey, List<String> stringList) async{
    _writes = _writes.then((void _) => _doAddList(kPrefKey,stringList));
    return _writes;
  }
}
static Future<void> _doAddList(String kPrefKey, List<String> list) async {
    List<String> cached = await load(kPrefKey);
    cached.addAll(list);
    await (await SharedPreferences.getInstance()).setStringList(kPrefKey, cached);
  }

Then I created another method to retrieve the list, I have also put the appropriate checks here, if empty or null:

 static Future<List<String>> load(String kPrefKey) async {
    return (await SharedPreferences.getInstance()).getStringList(kPrefKey) ??
        [];
  }

As I used it, I needed to add more methods. Methods to:

Clear the list.
Enter one string at a time
Override the list
Check if an element exists
Take the first item on the list.
Save an item at the top of the list.

In this way the class eventually became like this:

class CashedUserData {
  static Future<void> _writes = Future.value();
  static Future<void> overrideListData(String kPrefKey, List<String> stringList) async{
    _writes = _writes.then((void _) => _doOverrideListData(kPrefKey,stringList));
    return _writes;
  }
  static Future<void> addlist(String kPrefKey, List<String> stringList) async{
    _writes = _writes.then((void _) => _doAddList(kPrefKey,stringList));
    return _writes;
  }
  static Future<void> save(String kPrefKey, String id) async{
    if(await CashedUserData.exist(kPrefKey, id))
      return;
    _writes = _writes.then((void _) => _doSave(kPrefKey,id));
    return _writes;
  }
  static Future<void> saveAsFirst(String kPrefKey, String id) async{
    List<String> actuaList = await load(kPrefKey);
    if(actuaList!=null &&  actuaList.length == 0 )
      return save(kPrefKey,id);
    if(actuaList.contains(id))
      actuaList.remove(id);
    
    if(actuaList.length>1)
      actuaList.removeAt(0);
    List<String> newlist = new List();
    newlist.add(id);
    newlist.addAll(actuaList);
    _writes = _writes.then((void _) => _doOverrideListData(kPrefKey,newlist));
    return _writes;
  }
  static Future<void> delete(String kPrefKey, String id) {
    _writes = _writes.then((void _) => _doDelete(kPrefKey,id));
    return _writes;
  }
  static Future<String> getFirst(String kPrefKey) async {
    List<String> dataList = (await SharedPreferences.getInstance()).getStringList(kPrefKey);
    return (dataList!=null && dataList.length>0) ? dataList[0] : "";
  }
  static Future<List<String>> load(String kPrefKey) async {
    return (await SharedPreferences.getInstance()).getStringList(kPrefKey) ??
        [];
  }
  static Future<bool> exist(String kPrefKey, String id) async {
    List<String> userDataList = (await SharedPreferences.getInstance()).getStringList(kPrefKey) ?? [];
    return (userDataList!=null &&  userDataList.length > 0) ? userDataList.contains(id) : false;
  }
  static Future<void> _doSave(String kPrefKey, String id) async {
    List<String> cached = await load(kPrefKey);
    cached.add(id);
    await (await SharedPreferences.getInstance()).setStringList(kPrefKey, cached);
  }
  static Future<void> _doDelete(String kPrefKey, String id) async {
    List<String> cached = await load(kPrefKey);
    cached.remove(id);
    await (await SharedPreferences.getInstance()).setStringList(kPrefKey, cached);
  }
 static Future<void> _doAddList(String kPrefKey, List<String> list) async {
    List<String> cached = await load(kPrefKey);
    cached.addAll(list);
    await (await SharedPreferences.getInstance()).setStringList(kPrefKey, cached);
  }
 static Future<void> _doOverrideListData(String kPrefKey, List<String> list) async {
    await (await SharedPreferences.getInstance()).setStringList(kPrefKey, list);
 }
  static update(String kPrefKey, String currentItem, String kindlemail) async{
    List<String> actuaList = await load(kPrefKey);
    if(actuaList!=null &&  actuaList.length > 0  )
    {
     try{actuaList[actuaList.indexOf(currentItem)] = kindlemail;} catch (e) {}
    }
    await overrideListData(kPrefKey, actuaList);
  }
}

By doing this I simplified the call points. Furthermore, if the plugin shared preference used changed, there would only be one place where to take action.