Is it possible to add an array or object to SharedPreferences on Android

Question

I have an ArrayList of objects that have a name and an icon pointer and I want to save it in SharedPreferences  How can I do   NOTE  I don t want to use Database

User · Answer

Shared preferences introduced a getStringSet and putStringSet methods in API Level 11  but that s not compatible with older versions of Android  which are still popular   and also is limited to sets of strings   Android does not provide better methods  and looping over maps and arrays for saving and loading them is not very easy and clean  specially for arrays  But a better implementation isn t that hard   package com example utils   import org json JSONObject  import org json JSONArray  import org json JSONException   import android content Context  import android content SharedPreferences   public class JSONSharedPreferences       private static final String PREFIX    json        public static void saveJSONObject Context c  String prefName  String key  JSONObject object            SharedPreferences settings   c getSharedPreferences prefName  0           SharedPreferences Editor editor   settings edit            editor putString JSONSharedPreferences PREFIX key  object toString             editor commit               public static void saveJSONArray Context c  String prefName  String key  JSONArray array            SharedPreferences settings   c getSharedPreferences prefName  0           SharedPreferences Editor editor   settings edit            editor putString JSONSharedPreferences PREFIX key  array toString             editor commit               public static JSONObject loadJSONObject Context c  String prefName  String key  throws JSONException           SharedPreferences settings   c getSharedPreferences prefName  0           return new JSONObject settings getString JSONSharedPreferences PREFIX key                     public static JSONArray loadJSONArray Context c  String prefName  String key  throws JSONException           SharedPreferences settings   c getSharedPreferences prefName  0           return new JSONArray settings getString JSONSharedPreferences PREFIX key                     public static void remove Context c  String prefName  String key            SharedPreferences settings   c getSharedPreferences prefName  0           if  settings contains JSONSharedPreferences PREFIX key                 SharedPreferences Editor editor   settings edit                editor remove JSONSharedPreferences PREFIX key               editor commit                        Now you can save any collection in shared preferences with this five methods  Working with JSONObject and JSONArray is very easy  You can use JSONArray  Collection copyFrom  public constructor to make a JSONArray out of any Java collection and use JSONArray s get methods to access the elements   There is no size limit for shared preferences  besides device s storage limits   so these methods can work for most of usual cases where you want a quick and easy storage for some collection in your app  But JSON parsing happens here  and preferences in Android are stored as XMLs internally  so I recommend using other persistent data store mechanisms when you re dealing with megabytes of data

User · Answer

Easy mode for complex object storage with using Gson google library  1   public static void setComplexObject Context ctx  ComplexObject obj       SharedPreferences preferences   PreferenceManager getDefaultSharedPreferences ctx       SharedPreferences Editor editor   preferences edit        editor putString  COMPLEX OBJECT  new Gson   toJson obj         editor commit       public static ComplexObject getComplexObject  Context ctx       SharedPreferences preferences   PreferenceManager getDefaultSharedPreferences ctx       String sobj   preferences getString  COMPLEX OBJECT            if sobj equals     return null      else return new Gson   fromJson sobj  ComplexObject class        1  http   code google com p google-gson

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You can use putStringSet  This allow you to save a HashSet in your preferences  just like this   Save  Set lt String gt  values   SharedPreferences sharedPref        mContext getSharedPreferences PREF KEY  Context MODE PRIVATE    Editor editor   sharedPref edit     editor putStringSet  YOUR KEY   values   editor apply      Retrive  SharedPreferences sharedPref        mContext getSharedPreferences PREF KEY  Context MODE PRIVATE    Editor editor   sharedPref edit     Set lt String gt  newList   editor getStringSet  YOUR KEY   null     The putStringSet allow just a Set and this is an unordered list

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The Simple way is  to convert it to JSON String as below example   Gson gson   new Gson    String json   gson toJson myObj     Then store the string in the shared preferences  Once you need it just get string from shared preferences and convert back to JSONArray or JSONObject as per your requirement

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Regardless of the API level  Check String arrays and Object arrays in SharedPreferences    SAVE ARRAY  public boolean saveArray String   array  String arrayName  Context mContext           SharedPreferences prefs   mContext getSharedPreferences  preferencename   0         SharedPreferences Editor editor   prefs edit          editor putInt arrayName    size   array length         for int i 0 i lt array length i              editor putString arrayName         i  array i          return editor commit             LOAD ARRAY  public String   loadArray String arrayName  Context mContext          SharedPreferences prefs   mContext getSharedPreferences  preferencename   0         int size   prefs getInt arrayName     size   0         String array     new String size         for int i 0 i lt size i              array i    prefs getString arrayName         i  null         return array

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To write  SharedPreferences prefs   PreferenceManager          getDefaultSharedPreferences this   JSONArray jsonArray   new JSONArray    jsonArray put 1   jsonArray put 2   Editor editor   prefs edit    editor putString  quot key quot   jsonArray toString     System out println jsonArray toString     editor commit     To Read  try       JSONArray jsonArray2   new JSONArray prefs getString  quot key quot    quot    quot         for  int i   0  i  lt  jsonArray2 length    i               Log d  quot your JSON Array quot   jsonArray2 getInt i   quot  quot            catch  Exception e        e printStackTrace       Other way to do same    Retrieve the values Gson gson   new Gson    String jsonText   Prefs getString  quot key quot   null   String   text   gson fromJson jsonText  String   class      EDIT  gso to gson     Set the values Gson gson   new Gson    List lt String gt  textList   new ArrayList lt String gt  data   String jsonText   gson toJson textList   prefsEditor putString  quot key quot   jsonText   prefsEditor apply     Using GSON in Java  public void saveArrayList ArrayList lt String gt  list  String key       SharedPreferences prefs   PreferenceManager getDefaultSharedPreferences activity       SharedPreferences Editor editor   prefs edit        Gson gson   new Gson        String json   gson toJson list       editor putString key  json       editor apply            public ArrayList lt String gt  getArrayList String key       SharedPreferences prefs   PreferenceManager getDefaultSharedPreferences activity       Gson gson   new Gson        String json   prefs getString key  null       Type type   new TypeToken lt ArrayList lt String gt  gt       getType        return gson fromJson json  type      Using GSON in Kotlin fun saveArrayList list  java util ArrayList lt String  gt    key  String         val prefs  SharedPreferences   PreferenceManager getDefaultSharedPreferences activity      val editor  Editor   prefs edit       val gson   Gson       val json  String   gson toJson list      editor putString key  json      editor apply      fun getArrayList key  String    java util ArrayList lt String  gt         val prefs  SharedPreferences   PreferenceManager getDefaultSharedPreferences activity      val gson   Gson       val json  String   prefs getString key  null      val type  Type   object   TypeToken lt java util ArrayList lt String  gt   gt       getType       return gson fromJson json  type

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I loaded an array of waist sizes  already created in my array xml  into my preferences xml file with the code below   array pant inch size is the id of the entire array      lt ListPreference   android title  choosepantsize   android summary  Choose Pant Size   android key  pantSizePref    android defaultValue  34    android entries   array pant inch size   android entryValues   array pant inch size    gt     This populated the menu with choices from the array  I set the default size as 34  so when the menu pops up  they see size 34 is pre-selected

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When I was bugged with this  I got the serializing solution where  you can serialize your string  But I came up with a hack as well   Read this only if you haven t read about serializing  else go down and read my hack  In order to store array items in order  we can serialize the array into a single string  by making a new class ObjectSerializer   copy the code from     www androiddevcourse com objectserializer html   replace everything except the package name    Entering data in Shared preference     the rest of the code on line 38 -   Put the next arg as this  so that if data is not retrieved it will return empty array we cant put empty string coz the container variable is an array not string   Coming to my Hack  -  Merge contents of array into a single string by having some symbol in between each item and then split it using that symbol when retrieving it  Coz adding and retrieving String is easy with shared preferences  If you are worried about splitting just look up  splitting a string in java     Note  This works fine if the contents of your array is of primitive kind like string  int  float  etc  It will work for complex arrays which have its own structure  suppose a phone book  but the merging and splitting would become a bit complex     PS  I am new to android  so don t know if it is a good hack  so lemme know if you find better hacks

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This is the shared preferences code i use successfully  Refer this link     public class MainActivity extends Activity    private static final int RESULT SETTINGS   1  Button button  public String a  dd     Override public void onCreate Bundle savedInstanceState    super onCreate savedInstanceState     button    Button  findViewById R id btnoptions     setContentView R layout activity main         showUserSettings          Override public boolean onCreateOptionsMenu Menu menu    getMenuInflater   inflate R menu settings  menu   return true       Override public boolean onOptionsItemSelected MenuItem item    switch  item getItemId       case R id menu settings   Intent i   new Intent this  UserSettingActivity class    startActivityForResult i  RESULT SETTINGS    break       return true      Override  protected void onActivityResult int requestCode  int resultCode  Intent data          super onActivityResult requestCode  resultCode  data     switch  requestCode     case RESULT SETTINGS   showUserSettings     break               private void showUserSettings      SharedPreferences sharedPrefs   PreferenceManager  getDefaultSharedPreferences this     StringBuilder builder   new StringBuilder      builder append   n Pet        sharedPrefs getString  prefpetname    NULL       builder append   n Address      sharedPrefs getString  prefaddress   NULL        builder append   n Your name       sharedPrefs getString  prefname    NULL       TextView settingsTextView    TextView  findViewById R id textUserSettings       settingsTextView setText builder toString                     HAPPY CODING

User · Answer

So from the android developer site on Data Storage      User Preferences      Shared preferences are not strictly for saving  user preferences   such as what ringtone a user has chosen  If you re interested in creating user preferences for your application  see PreferenceActivity  which provides an Activity framework for you to create user preferences  which will be automatically persisted  using shared preferences     So I think it is okay since it is simply just key-value pairs which are persisted   To the original poster  this is not that hard  You simply just iterate through your array list and add the items  In this example I use a map for simplicity but you can use an array list and change it appropriately      my list of names  icon locations Map lt String  String gt  nameIcons   new HashMap lt String  String gt     nameIcons put  Noel     location to noel icon png    nameIcons put  Bob    another location to bob icon png    nameIcons put  another name    last location icon png     SharedPreferences keyValues   getContext   getSharedPreferences  name icons list   Context MODE PRIVATE   SharedPreferences Editor keyValuesEditor   keyValues edit     for  String s   nameIcons keySet             use the name as the key  and the icon as the value     keyValuesEditor putString s  nameIcons get s      keyValuesEditor commit     You would do something similar to read the key-value pairs again  Let me know if this works   Update  If you re using API level 11 or later  there is a method to write out a String Set

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For writing    private  lt T gt  void storeData String key  T data        ByteArrayOutputStream serializedData   new ByteArrayOutputStream         try           ObjectOutputStream serializer   new ObjectOutputStream serializedData           serializer writeObject data         catch  IOException e            e printStackTrace               SharedPreferences sharedPreferences   getSharedPreferences TAG  0       SharedPreferences Editor edit   sharedPreferences edit         edit putString key  Base64 encodeToString serializedData toByteArray    Base64 DEFAULT        edit commit        For reading   private  lt T gt  T getStoredData String key        SharedPreferences sharedPreferences   getSharedPreferences TAG  0       String serializedData   sharedPreferences getString key  null       T storedData   null      try           ByteArrayInputStream input   new ByteArrayInputStream Base64 decode serializedData  Base64 DEFAULT            ObjectInputStream inputStream   new ObjectInputStream input           storedData    T inputStream readObject          catch  IOException ClassNotFoundException java lang IllegalArgumentException e            e printStackTrace               return storedData

[android] Is it possible to add an array or object to SharedPreferences on Android

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