CODEWITHSUNDEEP
androidarraylistsharedpreferencesgson
user2688158
user2688158

Reputation: 417

Where to save the Arraylist of Objects using Gson and SharedPreferences so that when back button is pressed the Arraylist's data is intact

In my application I am trying to save an ArrayList using SharedPreference and Gson jar file. The Arraylist has objects of Person class which implements Serializable. I want the ArrayList to retain its data when back button is pressed.I have seen a lot of code on Internet but nothing suits me particularly. I have written part of the code seeing various solutions but I'm unsure of where to use it and my code also needs a bit of correction but I am unable to do it because I do not have much experience in programming.

Here is part of my code:

//Saving the arraylist

 SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
    Editor editor = prefs.edit();
    Gson gson = new Gson();
    //String json = gson.toJson(RecipientArray);
    for(Person p:RecipientArray){
        String json = gson.toJson(p);
        editor.putString("RecList", json);
    }

    editor.commit();

//Retrieving the values

SharedPreferences prefs =    PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
    String json = prefs.getString("RecList", "");
    Gson gson = new Gson();
    Person p = gson.fromJson(json, Person.class);
    RecipientArray.add(p); //RecipientArray is an ArrayList<Person>

Here I am not sure of how to get all Person objects saved earlier. Also I am not sure of where to put these pieces of code. Please help me as soon as possible.

Thanks.

Upvotes: 0

Views: 2144

Answers (1)

henry4343
henry4343

Reputation: 3921

This code have a problem, because your only put one key "RecList" so that you will put last one Person p to SharedPreferences.

   SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
        Editor editor = prefs.edit();
        Gson gson = new Gson();
        //String json = gson.toJson(RecipientArray);
        for(Person p:RecipientArray){
            String json = gson.toJson(p);
            editor.putString("RecList", json);
        }
    editor.commit();

maybe you can change your key like "RecList_"+number and also save your array.size

   SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
        Editor editor = prefs.edit();
        Gson gson = new Gson();
        //String json = gson.toJson(RecipientArray);
        for(int i = 0; i < RecipientArray.size(); i++)
            String json = gson.toJson(RecipientArray.get(i));
            editor.putString("RecList_"+i, json);
            editor.putInt("size",i);
        }
    editor.commit();

so you can get all string in your SharedPreferences like this 

SharedPreferences prefs =    PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
int size = prefs.getInt("size");
for(int i = 0;i<size;i++) {
    String json = prefs.getString("RecList_"+i, "");
    Gson gson = new Gson();
    Person p = gson.fromJson(json, Person.class);
    RecipientArray.add(p); //RecipientArray is an ArrayList<Person>
}

Upvotes: 3

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