RecyclerView中的更新项目

Question

I have an api that returns me items per page, in this case I always ask it to send me 12 items if the items received are equal to 12 the page is increased, if not kept. I have the following example where my api I sent the page 1 but in this case it returns 4 items which I show in my RecyclerView, after pressing my button to get more data returns me 6 items ie the 4 anterios and 2 more. What I want to do is compare the data that the api returns with those of the RecyclerView and only add the different items to it. Example:

first call data -> A B C D are added to the RecyclerView
second call data -> A B C D E F
compare data from call 1 with call 2 and add E F because they are different

the final result to be shown in the RecyclerView would be the following A B C D E F

this is my code:

mData.remove(position);
notifyItemRemoved(position);
notifyItemRangeChanged(position, mData.size());
notifyDataSetChanged();
//this lines deletes the final button, and after add the new data 
JSONArray res = response_json.getJSONArray("res");
for(int i=0;i<mData.size();i++){
    if(i >= row_index){ //row_index I identify the index of the page to update from it
        for(int j=0;j<res.length();j++){
            JSONObject item = res.getJSONObject(j);
            if(mData.get(i).getId() != item.getInt("id")){
                //add diferent data
                obj = new Obj();
                obj.setId_pedido(item.getInt("id"));
                obj.setValor(item.getString("valor"));
                mData.add(obj);
                notifyDataSetChanged();
            }
        }
    }
}
Obj mas = new Obj();
mas.setId_pedido(0);
mas.setValor("OBtener mas data");
mData.add(mas);
//Add the final button

All that I do in my adapter because the button I always add at the end as the last item. When running it does not work, my app freeze. How can I solve that?

Thank you very much for your time and assistance on this matter.

Answer 1

The problem is because you always refresh the RecyclerView adapter when you don't need it.

This code isn't good:

mData.remove(position);
notifyItemRemoved(position);
notifyItemRangeChanged(position, mData.size());
notifyDataSetChanged();

because you're telling the adapter to refresh itself 3 times. You only need call the following code whenever you remove an item:

mData.remove(position);
notifyItemRemoved(position);

You're also telling the adapter to update all the items whenever you add an item:

JSONArray res = response_json.getJSONArray("res");
for(int i=0;i<mData.size();i++){
    ...
        for(int j=0;j<res.length();j++){
            JSONObject item = res.getJSONObject(j);
            if(mData.get(i).getId() != item.getInt("id")){
                //add diferent data
                ...
                mData.add(obj);
                notifyDataSetChanged();
            }
        }
    ...
}

which simply means you're telling the adapter to refresh all the items x times. Where x is your total new items. This will freezing your UI for a while.

So, you need to update the adapter only when you've finished adding the items. Something like this:

JSONArray res = response_json.getJSONArray("res");
for(int i=0;i<mData.size();i++){
    ...
        for(int j=0;j<res.length();j++){
            ...
            if(mData.get(i).getId() != item.getInt("id")){
                ...
                mData.add(obj);
            }
        }
    ...
}

notifyDataSetChanged();