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。

Android商城开发----点击加入购物车，购物车商品的增删减
- 本文主要实现的功能是：
- 用到的主要知识点：
- 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
    - 2）购物车数据库ShoppingCarDatabase.java
  - 2.封装类
  - - 1）Goods.java 类：商品类，用于封装对商品的操作
    - 2）Car.java类，购物车类
    - 3）MyApplication.java 创建全局context
  - 3.分类和购物车
  - - 1）CategoryRightAdapter.java
    - 2）购物车页面
    - ShoppingCarFragment.java
    - ShoppingCarAdapter.java
  - 3.购物车布局页面
  - - fragment_shoppingcar.xml
    - 购物车RecyclerView的 list ShoppingCar_list.xml

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);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL(CREATE_GOODS_SQL);Log.i(TAG, "onCreate: 商品列表数据库创建成功");}@Overridepublic 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);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL(CREATE_GOODS_SQL);Log.i(TAG, "onCreate: 购物车数据库创建成功啦！");}@Overridepublic 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1Log.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1int 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;@Overridepublic void onCreate() {super.onCreate();context = getApplicationContext();}public static Context getContext(){return context;}
}

需要在AndroidManifest.xml指定：

<applicationandroid: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() {@Overridepublic void onClick(View v) {int pos = holder.getLayoutPosition();mOnItemClickListener.ImageButtonClickListener(holder.itemView, pos);//点击识别当前商品idint 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;@Overridepublic 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() {@Overridepublic void ItemClickListener(View view, int position) {Intent intent = new Intent(getActivity(), GoodsDetails.class);startActivity(intent);}//长摁事件@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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@Overridepublic 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okhttpHttpUtil.sendOkHttpRequest(url, json.toString(), new okhttp3.Callback() {//异常处理@Overridepublic void onFailure(@NonNull Call call, @NonNull IOException e) {e.printStackTrace();//打印异常httpError();                 //对异常情况处理}@Overridepublic 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dataJSONArray 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@Overridepublic void onResume() {super.onResume();upShoppingCarAdapter();}@Overridepublic void onDestroyView() {super.onDestroyView();binding = null;}@Overridepublic 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ContextView 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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic void onClick(View v) {//获取当前点击item的位置posint pos = holder.getLayoutPosition();sOnItemClickListener.ItemClickListener(holder.itemView, pos);}});//长摁删除购物车商品holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {@Overridepublic boolean onLongClick(View v) {if(sOnItemClickListener != null){//获取当前点击item的位置posint pos =holder.getLayoutPosition();sOnItemClickListener.ItemLongClickListener(holder.itemView,pos);}return false;}});}}//返回长度@Overridepublic 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"?>
<RelativeLayoutxmlns: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.RecyclerViewandroid:id="@+id/shoppingCar"android:layout_width="match_parent"android:layout_height="match_parent"android:layout_marginBottom="110dp"tools:ignore="MissingConstraints" /><LinearLayoutandroid: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 --><TextViewandroid:id="@+id/text_all_price"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="4"android:textColor="#D00000"android:textSize="25sp"/><Buttonandroid: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--><CheckBoxandroid: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.CardViewandroid: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"><RelativeLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:layout_toRightOf="@+id/shoppingCar_checkbox"><ImageViewandroid:id="@+id/shoppingCar_icon"android:layout_width="80dp"android:layout_height="80dp"android:scaleType="fitCenter" /><TextViewandroid:id="@+id/shoppingCar_title"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_toRightOf="@+id/shoppingCar_icon"android:paddingLeft="5dp" /><LinearLayoutandroid: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"><TextViewandroid: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" /><ImageButtonandroid: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" /><TextViewandroid:id="@+id/shoppingCar_num"android:layout_width="0dp"android:layout_height="30dp"android:layout_weight="0.8"android:gravity="center" /><ImageButtonandroid: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！