2022-11-13学习内容

1.案例-购物车-购物车列表展示

1.1ShoppingCartActivity.java

package com.example.chapter06;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.example.chapter06.database.ShoppingDBHelper;
import com.example.chapter06.entity.CartInfo;
import com.example.chapter06.entity.GoodsInfo;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ShoppingCartActivity extends AppCompatActivity {

    private TextView tv_count;
    private LinearLayout ll_cart;
    private ShoppingDBHelper mDBHelper;
    // 声明一个购物车中的商品信息列表
    private List<CartInfo> mCartList;
    // 声明一个根据商品编号查找商品信息的映射，把商品信息缓存起来，这样不用每一次都查询数据库
    private Map<Integer, GoodsInfo> mGoodsMap = new HashMap<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shopping_cart);
        TextView tv_title = findViewById(R.id.tv_title);
        tv_title.setText("购物车");
        ll_cart = findViewById(R.id.ll_cart);

        tv_count = findViewById(R.id.tv_count);
        tv_count.setText(String.valueOf(MyApplication.getInstance().goodsCount));

        mDBHelper = ShoppingDBHelper.getInstance(this);
    }

    @Override
    protected void onResume() {
        super.onResume();
        showCart();
    }

    // 展示购物车中的商品列表
    private void showCart() {
        // 移除下面的所有子视图
        ll_cart.removeAllViews();
        // 查询购物车数据库中所有的商品记录
        mCartList = mDBHelper.queryAllCartsInfo();
        if (mCartList.size() == 0) {
            return;
        }
        for (CartInfo info : mCartList) {
            // 根据商品编号查询商品数据库中的商品记录
            GoodsInfo goods = mDBHelper.queryGoodsInfoById(info.goodsId);
            mGoodsMap.put(info.goodsId, goods);
        }
    }
}

1.2ShoppingDBHelper.java新增内容：

// 查询购物车中所有的信息列表
    public List<CartInfo> queryAllCartsInfo() {
        List<CartInfo> list = new ArrayList<>();
        Cursor cursor = mRDB.query(TABLE_CART_INFO, null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            CartInfo info = new CartInfo();
            info.id = cursor.getInt(0);
            info.goodsId = cursor.getInt(1);
            info.count = cursor.getInt(2);
            list.add(info);
        }
        return list;
    }

    // 根据商品ID查询商品信息
    public GoodsInfo queryGoodsInfoById(int goodsId) {
        GoodsInfo info = null;
        Cursor cursor = mRDB.query(TABLE_GOODS_INFO, null, "_id=?", new String[]{String.valueOf(goodsId)}, null, null, null);
        if (cursor.moveToNext()) {
            info = new GoodsInfo();
            info.id = cursor.getInt(0);
            info.name = cursor.getString(1);
            info.description = cursor.getString(2);
            info.price = cursor.getFloat(3);
            info.picPath = cursor.getString(4);
        }
        return info;
    }