從服務器通過API傳輸數據完成后，如何使用遠程數據構建recyclerview

Question

我在片段中構建了一個回收視圖。 要在 recyclerview 中填充的數據存儲在遠程服務器中，並通過 JSON 進行解析。

我正在使用 Retrofit 將數據從服務器傳輸到應用程序。 注意：我是 Android 開發初學者，第一次通過看教程使用 Retrofit。

到目前為止，我已經理解了以下內容，如果我錯了，請糾正我由於 Retrofit 庫使用另一個線程而不是主線程來從服務器獲取響應，數據完全傳輸需要幾秒鍾，但直到那時 recyclerview 已經構建帶有空的 ArrayList。

所以，我的問題是，如何保持 recyclerView 從構建到數據傳輸完成？ 或如何在數據傳輸完成后更新空的 ArrayList 並從該數據填充 recyclerview？ 或者你可以告訴我什么是達到預期結果的最好和最有效的方法。

我已經嘗試過adapter.notifyDataSetChanged() ，但是我沒有在正確的地方使用它，或者我沒有以正確的方式使用它，因為它不起作用。 你可以在代碼中看到它。

庫片段：-

package com.diginfoexpert.mybooks.Fragment;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.diginfoexpert.mybooks.Activity.CategoryActvity;
import com.diginfoexpert.mybooks.Adapter.LibraryCategoriesCardAdapter;
import com.diginfoexpert.mybooks.Model.Category;
import com.diginfoexpert.mybooks.Model.LibraryAPI;
import com.diginfoexpert.mybooks.Model.LibraryCategories;
import com.diginfoexpert.mybooks.R;

import java.util.ArrayList;

import Controllers.JSONApiHolder;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.Retrofit.Builder;
import retrofit2.converter.gson.GsonConverterFactory;

public class LibraryFragment extends Fragment implements LibraryCategoriesCardAdapter.CategoryClickListener {

    private JSONApiHolder jsonApiHolder;
    ArrayList<Category> categories = new ArrayList<>();
    LibraryCategoriesCardAdapter adapter;
    RecyclerView recyclerView;


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_library, container, false);
        Log.d("RETROFIT", "onCreateView: Library Fragment Started");

        recyclerView = view.findViewById(R.id.library_category_recycler_view);

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://myurl.in/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        jsonApiHolder = retrofit.create(JSONApiHolder.class);

        getCategories();

        buildRecyclerView();

        return view;
    }

    private void buildRecyclerView() {
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
        adapter = new LibraryCategoriesCardAdapter(buildCategoryList(),this);
        recyclerView.setLayoutManager(linearLayoutManager);
        recyclerView.setAdapter(adapter);
    }

    private void getCategories() {
        Call<LibraryAPI> call = jsonApiHolder.getLibrary();

        call.enqueue(new Callback<LibraryAPI>() {
            @Override
            public void onResponse(Call<LibraryAPI> call, Response<LibraryAPI> response) {
                if(!response.isSuccessful()){
                    Log.d("RETROFIT", "onResponse: callback failed");
                    return;
                }

                else{
                    Log.d("RETROFIT", "onResponse: callback successful");
                    LibraryAPI libraryAPI = response.body();
                    categories = libraryAPI.getCategories();
                    adapter.notifyDataSetChanged();

                    for (Category category :categories){
                        Log.d("RETROFIT", "onResponse: "+category.getTitle());
                    }

                }
            }

            @Override
            public void onFailure(Call<LibraryAPI> call, Throwable t) {
                Log.d("RETROFIT", "onFailure: response failed : " +t.getMessage());
            }
        });
    }

    private ArrayList<Category> buildCategoryList() {
        ArrayList<Category> mList = new ArrayList<>();
//        mList.add(new Category("Art"));
//        mList.add(new Category("Action"));
//        mList.add(new Category("Thrill"));
//        mList.add(new Category("Fiction"));
//        mList.add(new Category("Romance"));
//        mList.add(new Category("Crime"));
//        mList.add(new Category("Classical"));
//        mList.add(new Category("Financial"));
//        mList.add(new Category("Business"));
        Log.d("RETROFIT", "Size of categories ArrayList "+categories.size());
        return categories;
    }

    @Override
    public void onCategoryClick() {
        Intent intent = new Intent(getActivity(), CategoryActvity.class);
        startActivity(intent);
    }
}

調試日志：-

2020-03-25 14:26:37.536 1703-1703/com.myurl.mybooks D/RETROFIT: onCreateView: Library Fragment Started
2020-03-25 14:26:37.630 1703-1703/com.myurl.mybooks D/RETROFIT: Size of categories ArrayList 0
2020-03-25 14:26:42.171 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: callback successful
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC Mains Syllabus
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER 1 PART "A" History
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER 1 PART "B" Geography
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER-2 (PART "A") Polity
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER 2 (PART "B") Economics & Social
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER 3 Science
2020-03-25 14:26:42.172 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC MAINS PAPER 4 Ethics
2020-03-25 14:26:42.173 1703-1703/com.myurl.mybooks D/RETROFIT: onResponse: MPPSC HINDI

Answer 1

這是您修改后的代碼部分

public void onResponse(Call<LibraryAPI> call, Response<LibraryAPI> response) {
                if(!response.isSuccessful()){
                    Log.d("RETROFIT", "onResponse: callback failed");
                    return;
                }

                else{
                    Log.d("RETROFIT", "onResponse: callback successful");
                    LibraryAPI libraryAPI = response.body();
                    categories = libraryAPI.getCategories();
                    adapter.notifyDataSetChanged();

                    for (Category category :categories){
                      categories.add(category) // Added by me  
                      Log.d("RETROFIT", "onResponse: "+category.getTitle());
                    }
                    adapter.notifyDataSetChanged() // Added by me
                }
            }

Answer 2

過了一段時間我找到了出路。 我在 main 方法中構建了回收器視圖，這是主線程。 當我們在改造中對網絡請求進行排隊時，它在不同的線程上工作，因此直到數據傳輸完成，回收器視圖已經構建在主線程中，沒有可用的數據。

因此，我沒有在主線程中構建回收器視圖，而是創建了一個方法來構建它。 在應用程序得到服務器響應后，我調用了該方法。

private void buildRecyclerView() {
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
        adapter = new LibraryCategoriesCardAdapter(buildCategoryList(),this);
        recyclerView.setLayoutManager(linearLayoutManager);
        recyclerView.setAdapter(adapter);
    }



private void getCategories() {
    Call<LibraryAPI> call = jsonApiHolder.getLibrary();

    call.enqueue(new Callback<LibraryAPI>() {
        @Override
        public void onResponse(Call<LibraryAPI> call, Response<LibraryAPI> response) {
            if(!response.isSuccessful()){
                Log.d("RETROFIT", "onResponse: callback failed");
                return;
            }

            else{
                Log.d("RETROFIT", "onResponse: callback successful");
                LibraryAPI libraryAPI = response.body();
                categories = libraryAPI.getCategories();
                buildRecyclerView();

                for (Category category :categories){
                    Log.d("RETROFIT", "onResponse: "+category.getTitle());
                }

            }
        }

        @Override
        public void onFailure(Call<LibraryAPI> call, Throwable t) {
            Log.d("RETROFIT", "onFailure: response failed : " +t.getMessage());
        }
    });
}