2022-11-11学习内容

1.案例-购物车-加入购物车

1.1MyApplication.java中新增内容：

// 购物车中的商品总数量
    public int goodsCount;

1.2CartInfo.java

package com.example.chapter06.entity;

// 购物车信息
public class CartInfo {
    public int id;
    // 商品编号
    public int goodsId;
    // 商品数量
    public int count;

    public CartInfo() {}

    public CartInfo(int id, int goodsId, int count) {
        this.id = id;
        this.goodsId = goodsId;
        this.count = count;
    }
}

1.3ShoppingDBHelper.java中新增内容：

// 添加商品到购物车
    public void insertCartInfo(int goodsId) {
        // 如果购物车中不存在该商品，添加一条信息
        CartInfo cartInfo = queryCartInfoByGoodsId(goodsId);
        ContentValues values = new ContentValues();
        values.put("goods_id", goodsId);
        if (cartInfo == null) {
            values.put("count", 1);
            mWDB.insert(TABLE_CART_INFO,null,values);
        } else {
            // 如果购物车中已经存在该商品，更新商品数量
            values.put("_id", cartInfo.id);
            values.put("count", ++cartInfo.count);
            mWDB.update(TABLE_CART_INFO,values,"_id=?",new String[]{String.valueOf(cartInfo.id)});
        }
    }

    private CartInfo queryCartInfoByGoodsId(int goodsId) {
        Cursor cursor = mRDB.query(TABLE_CART_INFO, null, "goods_id=?", new String[]{String.valueOf(goodsId)}, null, null, null);
        CartInfo info = null;
        if (cursor.moveToNext()) {
            info = new CartInfo();
            info.id = cursor.getInt(0);
            info.goodsId = cursor.getInt(1);
            info.count = cursor.getInt(2);
        }
        return info;
    }

    // 统计购物车中商品的总数量
    public int countCartInfo() {
        int count = 0;
        String sql = "select sum(count) from " + TABLE_CART_INFO;
        Cursor cursor = mRDB.rawQuery(sql, null);
        if (cursor.moveToNext()) {
            count = cursor.getInt(0);
        }
        return count;
    }

1.4ShoppingChannelActivity.java：

package com.example.chapter06;

import androidx.appcompat.app.AppCompatActivity;

import android.net.Uri;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.GridLayout;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.example.chapter06.database.ShoppingDBHelper;
import com.example.chapter06.entity.GoodsInfo;
import com.example.chapter06.util.ToastUtil;

import java.util.List;

public class ShoppingChannelActivity extends AppCompatActivity {

    // 声明一个商品数据库的帮助器对象
    private ShoppingDBHelper mDBHelper;
    private TextView tv_count;
    private GridLayout gl_channel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shopping_channel);
        TextView tv_title = findViewById(R.id.tv_title);
        tv_title.setText("手机商场");

        tv_count = findViewById(R.id.tv_count);
        gl_channel = findViewById(R.id.gl_channel);
        mDBHelper = ShoppingDBHelper.getInstance(this);
        mDBHelper.openReadLink();
        mDBHelper.openWriteLink();

        // 从数据库查询出商品信息，并展示
        showGoods();
    }

    @Override
    protected void onResume() {
        super.onResume();
        // 查询购物车商品总数，并展示
        showCartInfoTotal();
    }

    // 查询购物车商品总数，并展示
    private void showCartInfoTotal() {
        int count = mDBHelper.countCartInfo();
        MyApplication.getInstance().goodsCount = count;
        tv_count.setText(String.valueOf(count));
    }

    private void showGoods() {
        // 商品条目是一个线性布局，设置布局的宽度为屏幕的一半
        int screenWidth = getResources().getDisplayMetrics().widthPixels;
        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(screenWidth / 2, LinearLayout.LayoutParams.WRAP_CONTENT);
        // 查询商品数据库中的所有商品记录
        List<GoodsInfo> list = mDBHelper.queryAllGoodsInfo();
        for (GoodsInfo info : list) {
            // 获取布局文件item_goods.xml的根视图
            View view = LayoutInflater.from(this).inflate(R.layout.item_goods, null);
            ImageView iv_thumb = view.findViewById(R.id.iv_thumb);
            TextView tv_name = view.findViewById(R.id.tv_name);
            TextView tv_price = view.findViewById(R.id.tv_price);
            Button btn_add = view.findViewById(R.id.btn_add);

            // 给控件设置值
            iv_thumb.setImageURI(Uri.parse(info.picPath));
            tv_name.setText(info.name);
            tv_price.setText(String.valueOf((int)info.price));

            // 添加到购物车
            btn_add.setOnClickListener(v -> {
                addToCart(info.id, info.name);
            });

            // 把商品视图添加到网格布局
            gl_channel.addView(view, params);
        }
    }

    // 把指定编号的商品添加到购物车
    private void addToCart(int goodsId, String goodsName) {
        // 购物车商品数量+1
        int count = ++MyApplication.getInstance().goodsCount;
        tv_count.setText(String.valueOf(count));
        mDBHelper.insertCartInfo(goodsId);
        ToastUtil.show(this, "已添加一部" + goodsName + "到购物车");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mDBHelper.closeLink();
    }
}

1.5效果：

 点击“加入购物车”，购物车徽标数量加一：

  多添加几个，然后结束掉进程，再次进入APP，可以看到购物车数量仍是正确的：

 查看数据库，可以看到数据库也是正确的，1号商品1个，2号商品6个：