Android商城开发----点击加入购物车，购物车商品的增删减

Android商城开发----点击加入购物车，购物车商品的增删减

上一章节：【分类页面】点击左侧类别，实现右侧对应类别商品的展示
本文是在上一章节基础上开发的，点击【分类】页面商品的加入购物车按钮，实现将商品加入购物车的功能。

本文主要实现的功能是：

1.点击加入购物车按钮，将商品加入购物车。
2.点击相同的商品加入购物车，修改购物车中该商品数量 +1。
3.点击购物车页面 商品数量调节按钮【+1】按钮，商品数量 +1。
4.点击购物车页面中商品数量调节按钮【-1】按钮，商品数量 -1。
5.长摁删除购物车中该商品。

用到的主要知识点：

1.布局： RecyclerView的使用、对应Adapter的配置
2.数据库的创建： 我用的是SQLite，以及数据库操作：增、删、减、查
这里创建两个数据库：
一是 商品列表数据库(用来存放商品信息：商品Id、Icon、标题、价格)方便加入购物车时，按照Id去查找商品信息；
二是 购物车数据库（保存商品Id以及商品数量），方便对购物车商品进行操作增删减同时退出Activity后再回来商品数量仍然是上次退出时的显示，不会清零。
3.OKHttp网络请求
4.Json数据解析
5.封装类：（把对一类的操作封装进一个类里，方便复用，实现面向对象的操作）
两个类：商品类【 定义字段：商品Id 商品Icon 商品名称 商品价格；定义方法：增 查】和购物车类【定义字段：carId没用到 可以不定义，商品Id 商品数量；定义方法：增 改（加1.减1） 删 查】
6.接口： RecyclerView中Item点击、长摁、Item内部按钮的接口定义与调用，在接口里定义是为了区分出点的是哪个position的按钮。

点击将商品加入购物车的业务流程

源码

1.数据库

1）商品列表数据库GoodsListDatabase.java

package com.domain.mainView.database;
/*
* 商品列表数据库，将网络请求返回来的数据放进来
* */
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.nfc.Tag;
import android.util.Log;
import androidx.annotation.Nullable;

public class GoodsListDatabase extends SQLiteOpenHelper {
    private static final String TAG=GoodsListDatabase.class.getSimpleName();
    //定义创建数据表dict的SQL语句
    //创建表时，定义的单个列的约束
    public static final String CREATE_GOODS_SQL=
            "create table goods(dbId integer ,dbIcon integer," +
                    "dbTitle text," +
                    "dbPrice text,UNIQUE(dbId))";
    //private Context mContext;
    //构造函数
    public GoodsListDatabase(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_GOODS_SQL);
        Log.i(TAG, "onCreate: 商品列表数据库创建成功");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists goods");
        onCreate(db);
    }
}

2）购物车数据库ShoppingCarDatabase.java

package com.domain.mainView.database;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import androidx.annotation.Nullable;
import java.io.DataOutputStream;
/*
 * 购物车数据库，点击加入购物车图片按钮将该商品id加入购物车
 * */
public class ShoppingCarDatabase extends SQLiteOpenHelper {
    private static final String TAG=ShoppingCarDatabase.class.getSimpleName();
    //定义创建数据表dict的SQL语句
    final String CREATE_GOODS_SQL=
            "create table shoppingCar(carId Integer primary key autoincrement,dbId Integer,dbNum Integer)";
    //构造函数
    public ShoppingCarDatabase(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_GOODS_SQL);
        Log.i(TAG, "onCreate: 购物车数据库创建成功啦！");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //更新数据库
        db.execSQL("drop table if exists shoppingCar");
        onCreate(db);
    }
}

2.封装类

1）Goods.java 类：商品类，用于封装对商品的操作

/*商品类

• 字段：商品Id 商品Icon 商品名称 商品价格
• 方法：增 查
• 通过网络请求获取商品信息 插入商品列表数据库
• 包含 对商品列表 加入商品方法和读取商品方法*/

package com.domain.mainView.mClass;

import android.annotation.SuppressLint;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import com.domain.mainView.MyApplication;
import com.domain.mainView.database.GoodsListDatabase;
/*商品类
* 字段：商品Id 商品Icon 商品名称 商品价格
* 方法：增 查
* 通过网络请求获取商品信息 插入商品列表数据库
* 包含 对商品列表 加入商品方法和读取商品方法*/

public class Goods {
    private int goodsId;
    private int goodsIcon;
    private String goodsTitle;
    private String goodsPrice;
    private static final String TAG = GoodsListDatabase.class.getSimpleName();

    public Goods() {
    }
    public Goods(int goodsId, int goodsIcon, String goodsTitle, String goodsPrice) {
        this.goodsId = goodsId;
        this.goodsIcon = goodsIcon;
        this.goodsTitle = goodsTitle;
        this.goodsPrice = goodsPrice;
    }
    public int getGoodsId() {
        return goodsId;
    }
    public int getGoodsIcon() {
        return goodsIcon;
    }
    public String getGoodsTitle() {
        return goodsTitle;
    }
    public String getGoodsPrice() {
        return goodsPrice;
    }
//插入商品 增
    public void addGoods(int id, int icon, String title, String price) {
        GoodsListDatabase goodsListDatabase = new GoodsListDatabase(MyApplication.getContext(), "goods.db", null, 2);
        SQLiteDatabase db = goodsListDatabase.getReadableDatabase();
        ContentValues values = new ContentValues();
        values.put("dbId", id);
        values.put("dbIcon", icon);
        values.put("dbTitle", title);
        values.put("dbPrice", price);
      //数据库构建中UNIQUE(dbId)与insert ignore into配合解决重复插入数据库的问题  
        String sql = "insert or ignore into goods(dbId,dbIcon,dbTitle,dbPrice)values('" + id + "','" + icon + "','" + title + "','" + price + "')";
        db.execSQL(sql);
        Log.i(TAG, "addGoods: 商品插入商品列表数据库成功拉！");
    }
    
    @SuppressLint("Range")
    //查找商品 查
    public Goods findGoods(int goodId) {
        GoodsListDatabase goodsListDatabase = new GoodsListDatabase(MyApplication.getContext(), "goods.db", null, 2);
        SQLiteDatabase db = goodsListDatabase.getWritableDatabase();
        String idNew = String.valueOf(goodId);
        int id = 0;
        int icon = 0;
        String title = "";
        String price = "";
        Cursor cursor = db.query("goods", null, "dbId= ?", new String[]{idNew}, null, null, null);
        if (cursor.moveToFirst()) {
            do {
                id = cursor.getInt(cursor.getColumnIndex("dbId"));
                icon = cursor.getInt(cursor.getColumnIndex("dbIcon"));
                title = cursor.getString(cursor.getColumnIndex("dbTitle"));
                price = cursor.getString(cursor.getColumnIndex("dbPrice"));
            } while (cursor.moveToNext());
        }
        Goods goods1 = new Goods(id, icon, title, price);
        Log.i(TAG, "findGoods: goods1" + goods1);
        Log.i(TAG, "findGoods: 读取购物车商品成功拉");
        cursor.close();
        return goods1;
    }
}

2）Car.java类，购物车类

package com.domain.mainView.mClass;

import static android.service.controls.ControlsProviderService.TAG;
import android.annotation.SuppressLint;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import com.domain.mainView.MyApplication;
import com.domain.mainView.database.ShoppingCarDatabase;
/*
* 购物车类
* 字段：carId没用到 可以不定义，商品Id 商品数量
* 方法：增 改（加1.减1） 删 查
*/

public class Car {
    private int carId;
    private int goodsId;
    private int goodsNum;
    public Car() {//无参构造函数
    }

    public Car(int carId, int goodsId, int goodsNum) {//有参构造函数
        this.carId = carId;
        this.goodsId = goodsId;
        this.goodsNum = goodsNum;
    }

    public int getCarId() {
        return carId;
    }

    public int getGoodsId() {
        return goodsId;
    }

    public int getGoodsNum() {
        return goodsNum;
    }

    //加入购物车
    public void addCar(int goodsId) {
        //创建数据库
        ShoppingCarDatabase shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        SQLiteDatabase db = shoppingCarDatabase.getReadableDatabase();
        //查询数据库是否已存在该商品
        Cursor cursor = db.rawQuery("select * from shoppingCar where dbId=? ", new String[]{String.valueOf(goodsId)});
        while (cursor.moveToNext()) {
            Log.i(TAG, "isDbIdExist1: 数据已存在");
            //已存在，更改数量加1，调用下面的addOne方法
            addOne(goodsId);
            db.close();
            return;
        }
        //不存在，执行插入，将该goodsId插入数据库，数量是1
        Log.i(TAG, "isDbIdExist1: 数据不存在");
        String sql = "insert into shoppingCar(dbId,dbNum)values('" + goodsId + "',1 )";
        db.execSQL(sql);
        db.close();
        Log.i(TAG, "addCar: 加入新商品成功！！！");
    }

	//获得购物车中该商品数量 查询操作
    @SuppressLint("Range")
    public int getGoodsCarNum(int goodsId) {
        ShoppingCarDatabase shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        SQLiteDatabase db = shoppingCarDatabase.getReadableDatabase();
        //初始化数量为1
        int goodsCarNum = 1;
        Cursor cursor = db.rawQuery("select * from shoppingCar where dbId = ?", new String[]{String.valueOf(goodsId)});
        if (cursor.moveToFirst()) {
            do {
                //遍历cursor对象，取出数据
                goodsCarNum = cursor.getInt(cursor.getColumnIndex("dbNum"));
                Log.i(TAG, "dbNum" + goodsCarNum);
            } while (cursor.moveToNext());
            cursor.close();
            Log.i(TAG, "readShoppingCarDatabase: 读取购物车数据库ID成功拉！");
        }
        return goodsCarNum;
    }

    //商品数量加一 增 
    public int addOne(int goodsId) {
        ShoppingCarDatabase shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        SQLiteDatabase db = shoppingCarDatabase.getReadableDatabase();
        ContentValues values = new ContentValues();
        goodsNum = getGoodsCarNum(goodsId) + 1;
        values.put("dbNum", goodsNum);
        db.update("shoppingCar", values, "dbId=?", new String[]{String.valueOf(goodsId)});
        Log.i(TAG, goodsId + "addCar: 数量加1" + goodsNum);
        db.close();
        return goodsNum;
    }

    //商品数量减一 减
    public int reduceOne(int goodsId) {
        ShoppingCarDatabase shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        SQLiteDatabase db = shoppingCarDatabase.getReadableDatabase();
        ContentValues values = new ContentValues();
        goodsNum = getGoodsCarNum(goodsId) - 1;
        values.put("dbNum", goodsNum);
        db.update("shoppingCar", values, "dbId=?", new String[]{String.valueOf(goodsId)});
        Log.i(TAG, goodsId + "addCar: 数量-1" + goodsNum);
        db.close();
        return goodsNum;
    }
    
    //删除商品
    public void deleteCar(int goodsId) {
        ShoppingCarDatabase shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        SQLiteDatabase db = shoppingCarDatabase.getReadableDatabase();
        db.delete("shoppingCar", "dbId=?", new String[]{String.valueOf(goodsId)});
    }
}

3）MyApplication.java 创建全局context

全局获取Context，查看《第一行Android代码》P457-P460
可以在Activity和Fragment之外的文件调用Context

package com.domain.mainView;

import android.app.Application;
import android.content.Context;

public class MyApplication extends Application {
    private static Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        context = getApplicationContext();
    }

    public static Context getContext(){
        return context;
    }
}

需要在AndroidManifest.xml指定：

<application
  android:name="com.example.networktest.MyApplication"
  ...>
</application>

3.分类和购物车

1）CategoryRightAdapter.java

分类页面右侧的adapter，在里面定义点击事件；主要是识别点击了哪个商品，将对应商品的商品Id加入购物车数据库。

//定义单击事件和长摁事件接口
    public interface OnItemClickListener {
        void ItemClickListener(View view, int position);
		//定义购物车图片按钮，在接口中定义是为了区分点的是哪个商品的按钮
        void ImageButtonClickListener(View view, int position);
    }

    public void setOnClickListener(OnItemClickListener listener) {
        this.mOnItemClickListener = listener;
    }

//在onBindViewHolder中定义【加入购物车】按钮的单击事件
//设置imagebutton的监听事件
//img_shoppingCar为实例化的图片按钮控件
        holder.img_shoppingCar.setOnClickListener(new ImageButton.OnClickListener() {
            @Override
            public void onClick(View v) {
                int pos = holder.getLayoutPosition();
                mOnItemClickListener.ImageButtonClickListener(holder.itemView, pos);
                //点击识别当前商品id
                int currentId = listId.get(position);
                Log.i(TAG, "currentId" + currentId);
                car.addCar(currentId);
                Log.i(TAG, "新商品加入购物车成功！");
                // }
            }
        });

位置如图：

2）购物车页面

ShoppingCarFragment.java

1.我是在购物车页面才创建了商品列表的数据库，通过http网络请求，获取商品列表信息，然后进行JSON数据解析，并将数据insert到商品列表的数据库里。（其实这一步应该在分类列表写，在分类里面获取数据并推进分类页面里，我的分类页面是写死的）。
2.读取购物车里的数据，然后根据购物车中的商品Id去商品数据库里匹配商品信息，将其加入购物车的adapter，进行购物车商品的展示。
3.长摁删除商品。

package com.domain.mainView.ui.shoppingcar;

import android.annotation.SuppressLint;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.os.Looper;
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.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;


import com.domain.mainView.mClass.Car;
import com.domain.mainView.mClass.Goods;
import com.domain.mainView.GoodsDetails;
import com.domain.mainView.MyApplication;
import com.domain.mainView.R;
import com.domain.mainView.ShoppingCarAdapter;
import com.domain.mainView.database.GoodsListDatabase;
import com.domain.mainView.database.ShoppingCarDatabase;
import com.domain.mainView.databinding.FragmentShoppingcarBinding;
import com.domain.mainView.okhttp.HttpUtil;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

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

import okhttp3.Call;
import okhttp3.Response;

public class ShoppingCarFragment extends Fragment {
    private static final String TAG = ShoppingCarFragment.class.getSimpleName();
    private FragmentShoppingcarBinding binding;
    private GoodsListDatabase goodsListDatabase;
    private ShoppingCarAdapter shoppingCarAdapter;
    private RecyclerView shopRecyclerView;
    private ShoppingCarDatabase shoppingCarDatabase;
    private List<Goods> shoppingCar = new ArrayList<>();


    View root;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        try {
            //发送Http请求
            sendRequestOkHttp();
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    //读取购物车数据库的数据(加入的商品id)
    private void readShoppingCarDatabase() {
        //创建购物车数据库
        shoppingCarDatabase = new ShoppingCarDatabase(getActivity(), "shoppingCar.db", null, 3);
        Cursor cursor = shoppingCarDatabase.getReadableDatabase().query("shoppingCar", null, null, null, null, null, null);
        if (cursor.moveToFirst()) {
            do {
                //遍历cursor对象，取出数据
                @SuppressLint("Range")
                int dbId = cursor.getInt(cursor.getColumnIndex("dbId"));
                Log.i(TAG, "dbId" + dbId);
                Goods goods = new Goods();
                shoppingCar.add(goods.findGoods(dbId));
            } while (cursor.moveToNext());
            cursor.close();
            Log.i(TAG, "readShoppingCarDatabase: 读取购物车数据库ID成功拉！");
        }
    }

    //加载布局，当fragment绘制界面组件时回调该方法
    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        binding = FragmentShoppingcarBinding.inflate(inflater, container, false);
        root = binding.getRoot();
        initView();
        readShoppingCarDatabase();
        //设置适配器
        upShoppingCarAdapter();
        return root;
    }

    //创建更新adapter方法
    private void upShoppingCarAdapter() {
        shoppingCarAdapter = new ShoppingCarAdapter(shoppingCar);
        shopRecyclerView.setAdapter(shoppingCarAdapter);
        shoppingCarAdapter.setOnClickListener(new ShoppingCarAdapter.OnItemClickListener() {
            @Override
            public void ItemClickListener(View view, int position) {
                Intent intent = new Intent(getActivity(), GoodsDetails.class);
                startActivity(intent);
            }

            //长摁事件
            @Override
            public void ItemLongClickListener(View view, int position) {
                //没实现
                AlertDialog alertDialog = new AlertDialog.Builder(getActivity()).create();
                alertDialog.setTitle("提示");
                alertDialog.setMessage("确定要删除该商品吗？");
                //取消按钮
                alertDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "否",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                alertDialog.cancel();
                                Log.i(TAG, "ItemLongClickListener: 点击了否");
                            }
                        });
                //确定按钮
                alertDialog.setButton(DialogInterface.BUTTON_POSITIVE, "是",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                Car car = new Car();
                                Goods goods = shoppingCar.get(position);

                                car.deleteCar(goods.getGoodsId());
                                readShoppingCarDatabase();
                                initView();
                                upShoppingCarAdapter();
                                Log.i(TAG, "ItemLongClickListener: 点击了是");
                            }
                        });
                alertDialog.show();
                Log.i(TAG, "ItemLongClickListener: 长摁删除");
            }

            //图片按钮点击事件
            @Override
            public void ImageButtonClickListener(View view, int position) {

            }
        });
    }
    //定义初始化
    private void initView() {
        shopRecyclerView = root.findViewById(R.id.shoppingCar);
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        shopRecyclerView.setLayoutManager(layoutManager);
    }

    //进行网络请求
    private void sendRequestOkHttp() throws JSONException {
        //构建post参数json格式
        JSONObject json = new JSONObject();
        json.put("category", "");
        //url 我把商品列表写在接口里面，通过http请求获取商品信息
        String url = "http://rap2api.taobao.org/app/mock/307955/example/goodsList";//这个url你们自己定义吧，里面包含商品Icon名字/商品Id/商品标题/商品价格
        //实例化类
        //类.方法 调用封装好的okhttp
        HttpUtil.sendOkHttpRequest(url, json.toString(), new okhttp3.Callback() {
            //异常处理
            @Override
            public void onFailure(@NonNull Call call, @NonNull IOException e) {
                e.printStackTrace();//打印异常
                httpError();                 //对异常情况处理
            }

            @Override
            public void onResponse(@NonNull Call call, @NonNull Response response) throws IOException {
                String responseData = response.body().string();
                //解析json文件
                parseJson(responseData);
            }
        });
    }

    //对异常进行处理
    private void httpError() {
        //此处进行UI操作 异常弹窗
        //Looper用来做子线程弹窗。网络请求是开辟子线程
        Looper.prepare();
        Toast.makeText(getActivity(), "网络请求发生异常", Toast.LENGTH_SHORT).show();
        Looper.loop();
    }

    //处理请求回来的数据 解析json数据
    private void parseJson(final String jsonData) {
        //解析对象
        JSONObject jsonObject;
        try {
            jsonObject = new JSONObject(jsonData);
            String resultCode = jsonObject.optString("resultCode");
            Log.i(TAG, "resultCode" + resultCode);
            String message = jsonObject.optString("message");
            Log.i(TAG, "message" + message);
            //当返回码为0时，再进行后面的操作
            if (resultCode.equals("0")) {
                Log.i(TAG, "商品信息请求成功");
                //继续解析里面内容data
                JSONArray jsonArray = jsonObject.getJSONArray("data");
                for (int i = 0; i < jsonArray.length(); i++) {
                    // JSON数组里面的具体-JSON对象
                    JSONObject goodsObject = jsonArray.getJSONObject(i);
                    int goodsId = goodsObject.optInt("goodsId");
                    int goodsIcon = goodsObject.optInt("goodsIcon");
                    String goodsTitle = goodsObject.optString("goodsTitle");
                    String goodsPrice = goodsObject.optString("goodsPrice");
                    //把解析的数据赋给变量，插入数据库
                    int id = goodsId;
                    int icon = goodsIcon;
                    String title = goodsTitle;
                    String price = goodsPrice;
                    //实例化Goods类，调用Goods的addGoods方法，将数据插入数据库
                    Goods goods = new Goods();
                    goods.addGoods(id, icon, title, price);
                }
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    //onResume方法是Activity第一次创建时 重新加载实例时调用 例如 我打开App第一个界面OnCreate完 就调用onResume 然后切换到下一个界面 第一个界面不finish 按Back键回来时 就调onResume
    //不调onCreate， 还有就是 App用到一半 有事Home键切出去了 在回来时调onResume
    @Override
    public void onResume() {
        super.onResume();
        upShoppingCarAdapter();
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }
}

ShoppingCarAdapter.java

这里主要定义了购物车页面加1减1按钮的单击事件（Bug是我没有判断数量是否小于0，你们可以自行判断一下）

package com.domain.mainView;

import android.annotation.SuppressLint;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.domain.mainView.database.ShoppingCarDatabase;
import com.domain.mainView.mClass.Car;
import com.domain.mainView.mClass.Goods;
import java.util.ArrayList;
import java.util.List;

public class ShoppingCarAdapter extends RecyclerView.Adapter<ShoppingCarAdapter.ViewHolder> {
    private OnItemClickListener sOnItemClickListener;
    ShoppingCarDatabase shoppingCarDatabase;
    private static final String TAG = ShoppingCarAdapter.class.getSimpleName();
    private List<Goods> mGoodsList;
    
    @NonNull
    @Override
    //页面创建的时候
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //绑定布局文件 这里的MyApplication.getContext()就是调用的全局Context
        View view = LayoutInflater.from(MyApplication.getContext()).inflate(R.layout.shoppingcar_list, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }
    @Override
    //滑动到子项的时候
    public void onBindViewHolder(@NonNull ViewHolder holder, @SuppressLint("RecyclerView") int position) {
        shoppingCarDatabase = new ShoppingCarDatabase(MyApplication.getContext(), "shoppingCar.db", null, 3);
        //为控件绑定内容
        Goods goods = mGoodsList.get(position);
        String intIcon = "icon" + goods.getGoodsIcon();
        int goodsIcon = MyApplication.getContext().getResources().getIdentifier(intIcon, "drawable", "com.domain.mainView");
        holder.img_icon.setBackgroundResource(goodsIcon);
        holder.text_title.setText(goods.getGoodsTitle());
        holder.text_price.setText(goods.getGoodsPrice());
        //第一个参数0代表直接获取值
        Car car = new Car();
        holder.text_num.setText(String.valueOf(car.getGoodsCarNum(goods.getGoodsId())));
        Log.i(TAG, "onBindViewHolder: goodsId" + goods.getGoodsId());
        Log.i(TAG, "onBindViewHolder: goodsId" + goods.getGoodsTitle());

        holder.btn_numAdd.setOnClickListener(new ImageButton.OnClickListener() {
            @Override
            public void onClick(View v) {
                int pos = holder.getLayoutPosition();
                sOnItemClickListener.ImageButtonClickListener(holder.itemView, pos);
                //更新购物车数据库数量加1，然后重新获取购物车数量
                holder.text_num.setText(String.valueOf(car.addOne(goods.getGoodsId())));
            }
        });
        holder.btn_numReduce.setOnClickListener(new ImageButton.OnClickListener() {
            @Override
            public void onClick(View v) {
                int pos = holder.getLayoutPosition();
                sOnItemClickListener.ImageButtonClickListener(holder.itemView, pos);
                //更新购物车数据库数量加1，然后重新获取购物车数量
                holder.text_num.setText(String.valueOf(car.reduceOne(goods.getGoodsId())));
            }
        });
        //如果监听事件不为空，回调相应的方法
        if (sOnItemClickListener != null) {
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    //获取当前点击item的位置pos
                    int pos = holder.getLayoutPosition();
                    sOnItemClickListener.ItemClickListener(holder.itemView, pos);
                }
            });
            //长摁删除购物车商品
            holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    if(sOnItemClickListener != null){
                        //获取当前点击item的位置pos
                        int pos =holder.getLayoutPosition();
                        sOnItemClickListener.ItemLongClickListener(holder.itemView,pos);
                    }
                    return false;
                }
            });
        }
    }
    //返回长度
    @Override
    public int getItemCount() {
        return mGoodsList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        //获取控件
        public ImageView img_icon;
        public TextView text_title, text_price, text_num;
        public ImageButton btn_numReduce, btn_numAdd;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            img_icon = itemView.findViewById(R.id.shoppingCar_icon);
            text_title = itemView.findViewById(R.id.shoppingCar_title);
            text_price = itemView.findViewById(R.id.shoppingCar_price);
            text_num = itemView.findViewById(R.id.shoppingCar_num);
            btn_numReduce = itemView.findViewById(R.id.btn_numReduce);
            btn_numAdd = itemView.findViewById(R.id.btn_numAdd);
        }
    }

    //构造函数 读取购物车数据库里的东西，add进去。
    public ShoppingCarAdapter(List<Goods> list) {
        mGoodsList = list;
        Log.i(TAG, "AdapterList" + list);
    }

    //定义单击事件和长摁事件接口
    public interface OnItemClickListener {
        void ItemClickListener(View view, int position);

        void ItemLongClickListener(View view, int position);
		//这里的ImageButton 为购物车页面的商品数量加减 两个图片按钮
        void ImageButtonClickListener(View view, int position);
    }

    public void setOnClickListener(ShoppingCarAdapter.OnItemClickListener listener) {
        this.sOnItemClickListener = listener;
    }
}

3.购物车布局页面

fragment_shoppingcar.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.shoppingcar.ShoppingCarFragment">
<-- 存放购物车商品的RecyclerView -->
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/shoppingCar"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="110dp"
        tools:ignore="MissingConstraints" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginRight="20dp"
        android:layout_marginLeft="20dp"
        android:layout_marginBottom="60dp"
        android:layout_alignParentBottom="true">
        <-- 总价格的TextView 这块还没实现 -->
        <TextView
            android:id="@+id/text_all_price"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="4"
            android:textColor="#D00000"
            android:textSize="25sp"/>
        <Button
            android:id="@+id/btn_confirm_order"
            android:layout_width="0dp"
            android:layout_weight="2"
            android:layout_height="wrap_content"
            android:text="确认订单" />
    </LinearLayout>
</RelativeLayout>

购物车RecyclerView的 list ShoppingCar_list.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto">
<--多选框-->
    <CheckBox
        android:id="@+id/shoppingCar_checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginLeft="5dp"
        android:layout_marginTop="37dp"
        android:theme="@style/MyCheckBox"/>
<--卡片式布局-->
    <androidx.cardview.widget.CardView
        android:layout_width="340dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="5dp"
        android:layout_marginTop="5dp"
        android:layout_marginEnd="5dp"
        android:layout_marginBottom="5dp"
        app:cardBackgroundColor="@color/white"
        android:layout_toRightOf="@+id/shoppingCar_checkbox"
        app:cardCornerRadius="20dp"
        app:contentPadding="15dp">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@+id/shoppingCar_checkbox">

            <ImageView
                android:id="@+id/shoppingCar_icon"
                android:layout_width="80dp"
                android:layout_height="80dp"
                android:scaleType="fitCenter" />

            <TextView
                android:id="@+id/shoppingCar_title"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_toRightOf="@+id/shoppingCar_icon"
                android:paddingLeft="5dp" />

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_below="@+id/shoppingCar_title"
                android:layout_alignBottom="@+id/shoppingCar_icon"
                android:layout_centerInParent="true"
                android:layout_marginRight="10dp"
                android:layout_toRightOf="@+id/shoppingCar_icon"
                android:gravity="bottom"
                android:paddingLeft="5dp">

                <TextView
                    android:id="@+id/shoppingCar_price"
                    android:layout_width="0dp"
                    android:layout_height="wrap_content"
                    android:layout_below="@+id/shoppingCar_title"
                    android:layout_toRightOf="@+id/shoppingCar_icon"
                    android:layout_weight="4"
                    android:textSize="16sp" />

                <ImageButton
                    android:id="@+id/btn_numReduce"
                    android:layout_width="0dp"
                    android:layout_height="30dp"
                    android:layout_weight="0.8"
                    android:background="#FFFFFFFF"
                    android:padding="0dp"
                    android:scaleType="fitCenter"
                    android:src="@drawable/shoppingcar_reduce_48" />

                <TextView
                    android:id="@+id/shoppingCar_num"
                    android:layout_width="0dp"
                    android:layout_height="30dp"
                    android:layout_weight="0.8"
                    android:gravity="center" />

                <ImageButton
                    android:id="@+id/btn_numAdd"
                    android:layout_width="0dp"
                    android:layout_height="30dp"
                    android:layout_weight="0.8"
                    android:background="#FFFFFFFF"
                    android:padding="0dp"
                    android:scaleType="fitCenter"
                    android:src="@drawable/shoppingcar_add_48" />
            </LinearLayout>
        </RelativeLayout>
    </androidx.cardview.widget.CardView>
</RelativeLayout>

还存在一些问题：
Bug1：数量加减那块，没有判断是否小于0
Bug2：长摁删除商品，后，页面会在下面加载一列商品列表，点击其他的Fragment再点回来就正常了，估计是我删除后的刷新页面位置没放对。

代码量有点多，可能会缺少一些配置信息，遇到什么问题可以私我也可以发表评论，看到会回复哒!
码字不易，点个赞吧！快去自己动手试试吧！