CODEWITHSUNDEEP
androidarraylistsharedpreferences
ansar abbas
ansar abbas

Reputation: 11

Retrieve Arraylist from Shared Preferences

I am working on shared Preferences. Basically, I am saving ArrayList to shared preferences which are working fine. Now I want to retrieve the ArrayList from Shared preferences but I am getting null. ArrayList is retrieving from preferences and also showing it's size. but data is not being set to string. How I retrieve the ArrayList from shared Preferences. here is my code 

public void saveRootCategory(List<Category> categories){
    preferences = mCtx.getSharedPreferences(SHARED_PREF_NAME, MODE_PRIVATE);
    editor = preferences.edit();
    editor.putInt("RootCategory",categories.size());
    for (int i=0;i<categories.size();i++){
        setData(categories.get(i));
    }
    editor.apply();
}
public void setData(final Category category){
    categoryId = category.getId();
    categoryName = category.getCategoryName();
    editor.putInt("CategoryId",categoryId);
    editor.putString("CategoryName",categoryName);
}
public  ArrayList<String> getRootCategoy() {
    preferences = mCtx.getSharedPreferences(SHARED_PREF_NAME, MODE_PRIVATE);
    ArrayList<String> rootCategories = new ArrayList<>();
    rootCategories.clear();
    int size = preferences.getInt("RootCategory", 0);
    for(int i=0;i<size;i++) {
        int Id = preferences.getInt("CategoryId" + i,0);
        String name = preferences.getString("CategoryName" + i ,"");
        rootCategories.add(String.valueOf(Id));
        rootCategories.add(name);
    }
    return rootCategories;
}

Upvotes: 0

Views: 184

Answers (6)

KevinDsoon
KevinDsoon

Reputation: 1

public void setData(final Category category)
The method use the same key("CategoryId", "CategoryName") to save every item in the list. However, you use "CategoryId" + index to get the value from SharedPreference.
Obviously, you can never get the right answer in this way...

@Murat's answer correct the method, and it can work well.
But I don't think it's a good way to save a List. If you do want to use SP to save Lists, I suggest Gson or any other way to translate your object into String first. It will work better.

Upvotes: 0

Suraj Vaishnav
Suraj Vaishnav

Reputation: 8305

Replace your both methods with these:

public void saveRootCategory(List<Category> categories){
    preferences = mCtx.getSharedPreferences(SHARED_PREF_NAME, MODE_PRIVATE);
    editor = preferences.edit();
    editor.putString("RootCategory",new Gson().toJson(categories));
    editor.apply();
}

public  ArrayList<Category> getRootCategoy() {
    preferences = mCtx.getSharedPreferences(SHARED_PREF_NAME, MODE_PRIVATE);
    String data = preferences.getString("RootCategory","");
    return new Gson().fromJson(data, new TypeToken<List<Category>>(){}.getType());
}

No third party library needed use Gson(inbuilt) library which can easily do what you want to achieve.

Upvotes: 0

Kevin Kurien
Kevin Kurien

Reputation: 842

I used to have the same null problem
Here's how I solved it
I have an arrayList named language 

language = new ArrayList<String>

I had to add everything the user writes on the edittext on button click not repeating any redundant value 

    if(!language.contains(value)) {
         language.add(value);
}

To save this arraylist I created a hashSet 

 Set<String> set = new HashSet<String>();

and save all of them onPause 

set.addAll(language);
.putStringSet("yourKey", set);
.commit();

and retrive it back to language array list onCreate 

prefs=this.getSharedPreferences("yourPrefsKey",Context.MODE_PRIVATE);
        edit=prefs.edit();
set = prefs.getStringSet("yourKey", null);
            language = new ArrayList<String>(set);
            edit.remove("yourKey").commit();

remember to remove everytime or it will again create null

Upvotes: 1

Rico
Rico

Reputation: 370

Add some breakpoints on setData() -> editor.putInt("CategoryId",categoryId); and debug your code are necessary.

BTW, it seems that there's no difference you call either editor.apply() or editor.commit() running on API 9 or above devices.

Upvotes: 0

Sunny
Sunny

Reputation: 3265

As you are trying to save the ArrayList into the share preference.

I Suggest you can use PaperDB Library.

Which is very fast and directly save your ArrayList same as preference doing.

You can also use it to store the Primitive datatypes and model class directly.

Note: It also reduces the code lines.

Upvotes: 0

Murat Karag&#246;z
Murat Karag&#246;z

Reputation: 37594

You are missing the index in setData. Change it to

public void setData(final Category category, int index){
    categoryId = category.getId();
    categoryName = category.getCategoryName();
    editor.putInt("CategoryId" + index, categoryId);
    editor.putString("CategoryName" + index, categoryName);
}

Upvotes: 0

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