java - Android List in SharedPreference -

i trying edit values list in sharedpreferences someting going wrong.

my sharedpreference is:

public class stepsdata {     static sharedpreferences data;     static sharedpreferences.editor editor;     static final int value_key = 0;     static final list<string> list_key= new vector<string>(); } 

i use sharedpref by:

stepsdata.data = getapplicationcontext().getsharedpreferences("userdata", mode_private); stepsdata.editor = stepsdata.data.edit(); 

if want edit or value value_key works by:

int step = stepsdata.data.getint(string.valueof(value_key), 0); editor.putint(string.valueof(value_key), 0).apply(); 

but have problem using list, code value is:

list<string> mylist = (list<string>) data.getstringset(string.valueof(list_key),null); 

and delete:

list<string> clearlist = new vector<string>(); editor.putstringset(string.valueof(list_key), (set<string>) clearlist).apply(); 

but there nullpointerexception. best way use ".clear()" on list sharedpreference , how is possible values list , size?

if want store list object in sharedpreference use gson library. use convert list object json format , store json string sharedpref.
first include line in gradle file(app level)

compile 'com.google.code.gson:gson:2.4'

below code set type list

type listtype = new typetoken<list<string>>(){}.gettype();  gson gson = new gson(); 

now create list object , convert json string format using gson object , type

list<string> mylist = new arraylist<>(); //add elements in mylist object  string jsonformat = gson.tojson(mylist,listtype);   //adding sharedpref   editor.put("list",jsonformat).apply(); 

now values sharedpref , convert json string list object.

//this line json string sharedpref , converted object of type list(specified in listtype object)  list<string> list = gson.fromjson(sharedpref.get("list",""),listtype);   //now modify list object par requirement , again same step of converting list object jsonformat.