How to save List<Object> to SharedPreferences?

Question

I have a list of products, which i retrieve from webservice, when app is opened for first time, app gets product list from webservice. I want to save this list to shared preferences.

    List<Product> medicineList = new ArrayList<Product>(); 

where Product class is:

public class Product {     public final String productName;     public final String price;     public final String content;     public final String imageUrl;      public Product(String productName, String price, String content, String imageUrl) {         this.productName = productName;         this.price = price;         this.content = content;         this.imageUrl = imageUrl;     } } 

how i can save this List not requesting from webservice each time?

Answer 1

It only possible to use primitive types because preference keep in memory. But what you can use is serialize your types with Gson into json and put string into preferences:

private static SharedPreferences sharedPreferences = context.getSharedPreferences(STORE_FILE_NAME, Context.MODE_PRIVATE);  private static SharedPreferences.Editor editor = sharedPreferences.edit();      public <T> void setList(String key, List<T> list) {     Gson gson = new Gson();     String json = gson.toJson(list);          set(key, json); }  public static void set(String key, String value) {     editor.putString(key, value);     editor.commit(); } 

Extra Shot from below comment by @StevenTB

To Retrive

 public List<YourModel> getList(){     List<YourModel> arrayItems;     String serializedObject = sharedPreferences.getString(KEY_PREFS, null);      if (serializedObject != null) {          Gson gson = new Gson();          Type type = new TypeToken<List<YourModel>>(){}.getType();          arrayItems = gson.fromJson(serializedObject, type);      } } 

Answer 2

You can use GSON to convert Object -> JSON(.toJSON) and JSON -> Object(.fromJSON).

• Define your Tags with you want (for example):

  private static final String PREFS_TAG = "SharedPrefs"; private static final String PRODUCT_TAG = "MyProduct"; 

• Get your sharedPreference to these tag's

  private List<Product> getDataFromSharedPreferences(){     Gson gson = new Gson();     List<Product> productFromShared = new ArrayList<>();     SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);     String jsonPreferences = sharedPref.getString(PRODUCT_TAG, "");          Type type = new TypeToken<List<Product>>() {}.getType();     productFromShared = gson.fromJson(jsonPreferences, type);      return preferences; } 

• Set your sharedPreferences

  private void setDataFromSharedPreferences(Product curProduct){     Gson gson = new Gson();     String jsonCurProduct = gson.toJson(curProduct);      SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);     SharedPreferences.Editor editor = sharedPref.edit();      editor.putString(PRODUCT_TAG, jsonCurProduct);     editor.commit(); } 

• If you want to save an array of Products, do this:

  private void addInJSONArray(Product productToAdd){      Gson gson = new Gson();     SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);      String jsonSaved = sharedPref.getString(PRODUCT_TAG, "");     String jsonNewproductToAdd = gson.toJson(productToAdd);      JSONArray jsonArrayProduct= new JSONArray();      try {         if(jsonSaved.length()!=0){             jsonArrayProduct = new JSONArray(jsonSaved);         }         jsonArrayProduct.put(new JSONObject(jsonNewproductToAdd));     } catch (JSONException e) {         e.printStackTrace();     }      //SAVE NEW ARRAY     SharedPreferences.Editor editor = sharedPref.edit();     editor.putString(PRODUCT_TAG, jsonArrayProduct);     editor.commit(); }