Maintain Drag & Dropped items position when restarting

Question

I have a RecyclerView - Grid, with drag & drop, using this code I've manage to achieve that, And made a lot of changes, only one problem, i can't save the dragged items position on restarting ( the app not the phone ). What i thought about is adding " int position " to my item.java constructor, but what i can't do is getting the changed position .

I'm using the same drag & drop codes provided in the link.

    ItemTouchHelper.Callback _ithCallback = new ItemTouchHelper.Callback() {
    //and in your imlpementaion of
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        // get the viewHolder's and target's positions in your adapter data, swap them
        Collections.swap(AllItems, viewHolder.getAdapterPosition(), target.getAdapterPosition());
        // and notify the adapter that its dataset has changed

        rcAdapter.notifyItemMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        //TODO
    }

    //defines the enabled move directions in each state (idle, swiping, dragging).
    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        return makeFlag(ItemTouchHelper.ACTION_STATE_DRAG,
                ItemTouchHelper.DOWN | ItemTouchHelper.UP | ItemTouchHelper.START | ItemTouchHelper.END);
    }
};

Here's the code in onCreate :

    ItemTouchHelper ith = new ItemTouchHelper(_ithCallback);
    ith.attachToRecyclerView(RcView);

Getting Duplicated items after position changing, Code :

    @Override
public void onStop()
{
    super.onStop();
    SharedPreferencesTools.setOrderedItems(this, AllItems);
}

getAllItemList :

private List<Item> getAllItemList(){
AllItems = SharedPreferencesTools.getOrderedItems(this);
//Add item .. etc 
//return items 

}

Answer 1

Just keep your modified collection AllItems in SharedPreferences and load it on the app start & store it back, once you get out of the app.

To do this, you need to serialize your collection to json by Gson and store as a String. And then deserialize it afterwards:

public final class SharedPreferencesTools {
    private static final String USER_SETTINGS_PREFERENCES_NAME = "UserSettings";
    private static final String ALL_ITEMS_LIST = "AllItemsList";
    private static Gson gson = new GsonBuilder().create();

    public static List<Item> getOrderedItems(Context context) {
        String stringValue = getUserSettings(context).getString(ALL_ITEMS_LIST, "");
        Type collectionType = new TypeToken<List<Item>>() {
        }.getType();
        List<Item> result = gson.fromJson(stringValue, collectionType);
        return (result == null) ? new ArrayList<Item>() : result;
    }

    public static void setOrderedItems(Context context, List<Item> items) {
        String stringValue = gson.toJson(items);

        SharedPreferences sharedPreferences = getUserSettings(context);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putString(ALL_ITEMS_LIST, stringValue);
        editor.apply();        
    }

    static SharedPreferences getUserSettings(Context context) {
        return context.getSharedPreferences(USER_SETTINGS_PREFERENCES_NAME, Context.MODE_PRIVATE);
    }
}

The usage of these two methods:

 SharedPreferencesTools.setOrderedItems(getActivity(), AllItems);
 ...
 List<Item> AllItems = SharedPreferencesTools.getOrderedItems(getActivity());