从内部类中添加对象到arraylist

Question

I am writing an app to fetch data from my online database using a callback function to a RecyclerView in my fragment . As you will see in my code below I have tried to show all the relevant pieces of code that are responsible for my final result down there. Should you require more information please ask so that I may provide it.

Here is one class called Question.java

public class Question {
    public Integer postid;
    public String title;
    public String content;
    public String tags;
    public String created;

}

then the callback class: CallbackQuestions.java

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import com.example.myapp;

public class CallbackQuestions implements Serializable{
    public int total = -1;
    public List<Question> data = new ArrayList<>();
}

My ItemModel class: ItemModel.java

public class ItemModel {
    private String Title;
    private String Description;
    private String Tags;
    private String Created;

    public ItemModel(String Title, String Description, String Tags, String Created) {
        this.Title = Title;
        this.Description = Description;
        this.Tags = Tags;
        this.Created = Created;
    }

    public String getCreated() {
        return Created;
    }

    public void setCreated(String Created) {
        this.Created = Created;
    }

    public String getTitle() {
        return Title;
    }

    public void setTitle(String Title) {
        this.Title = Title;
    }

    public String getDescription() {
        return Description;
    }

    public void setDescription(String Description) {
        this.Description = Description;
    }

    public String getTags() {
        return Tags;
    }

    public void setTags(String Tags) {
        this.Tags = Tags;
    }
}

Then lastly here is what is giving me headache to get it working ListingModel.java

@Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        ListingModel listingModel = mArrayList.get(position);

        ((NormalViewHolder) holder).tv_card_header.setText(mArrayList.get(position).getHeader());

        ((NormalViewHolder) holder).listing_recycler_view.setHasFixedSize(true);
        RecyclerView.LayoutManager normalLayoutManager = new LinearLayoutManager(context, LinearLayoutManager.VERTICAL, false);
        ((NormalViewHolder) holder).listing_recycler_view.setLayoutManager(normalLayoutManager);

        ArrayList<ItemModel> list = loadQuestionsList();

        ItemAdapter itemAdapter = new ItemAdapter(list);
        ((NormalViewHolder) holder).listing_recycler_view.setAdapter(itemAdapter);

        Log.d("MyAdapter", "position: " + position);
    }

    public ArrayList<ItemModel> loadQuestionsList() {
        final ArrayList<ItemModel> mArrayList = new ArrayList<>();
        int start = 0;
        String sort = "recent";
        API api = CallJson.callJson();
        Call<CallbackPosts> callbackQuestionsCall = api.QuestionsAll(BaseUrlConfig.RequestLoadMore, start, sort);
        callbackQuestionsCall.enqueue(new Callback<CallbackQuestions>() {
            @Override
            public void onResponse(Call<CallbackQuestions> call, Response<CallbackQuestions> response) {
                CallbackQuestions callbackQuestions = response.body();
                for (QuestionsAll thisQuestion : callbackQuestions.data){
                    mArrayList.add(new ItemModel(thisQuestion.Title, thisQuestion.Description, thisQuestion.Tags, thisQuestion.Created));
                }
                 myArrayList = mArrayList;
            }

            @Override
            public void onFailure(Call<CallbackQuestions> call, Throwable t) {
                if (!call.isCanceled());
            }
        });
        return myArrayList;
    }

The problem is that my ArrayLists is not returning anything at all despite the callback running successfully as per logs. I would appreciate your help so much.

Answer 1

I think i agree with the comment you got on earlier, your function will always return an empty list. Asynchronous calls don't work that way. There is no return value.

Don't make API calls inside the ListingModel. Fetch the data first. Then pass it into the ListingModel. You can have an update() method that receives the list of items fetched and forces a refresh of the ListingModel.

On ItemAdapter create a method that set the list and notify the adapter to refresh by calling notifyDataSetChanged(); Then call that method inside the success response if the list fetched is not empty. ie itemAdapter.setList(myArrayList).