2022-11-10学习内容

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.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 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 View 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();
    }

    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);
            // 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));

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

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

package com.example.chapter06.database;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import com.example.chapter06.entity.GoodsInfo;

import java.util.ArrayList;
import java.util.List;

public class ShoppingDBHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "shopping.db";
    // 商品信息表
    private static final String TABLE_GOODS_INFO = "GOODS_INFO";
    // 购物车信息表
    private static final String TABLE_CART_INFO = "CART_INFO";
    private static final int DB_VERSION = 1;
    private static ShoppingDBHelper mHelper = null;
    private SQLiteDatabase mRDB = null;
    private SQLiteDatabase mWDB = null;

    private ShoppingDBHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    // 打开数据库的读连接
    public SQLiteDatabase openReadLink() {
        if (mRDB == null || !mRDB.isOpen()) {
            mRDB = mHelper.getReadableDatabase();
        }
        return mRDB;
    }

    // 打开数据库的写连接
    public SQLiteDatabase openWriteLink() {
        if (mWDB == null || !mWDB.isOpen()) {
            mWDB = mHelper.getWritableDatabase();
        }
        return mWDB;
    }

    // 关闭数据库连接
    public void closeLink() {
        if (mRDB != null && mRDB.isOpen()) {
            mRDB.close();
            mRDB = null;
        }
        if (mWDB != null && mWDB.isOpen()) {
            mWDB.close();
            mWDB = null;
        }
    }

    // 利用单例模式获取数据库帮助器的唯一实例
    public static ShoppingDBHelper getInstance(Context context) {
        if (mHelper == null) {
            mHelper = new ShoppingDBHelper(context);
        }
        return mHelper;
    }

    // 创建数据库，执行建表语句
    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建商品信息表
        String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_GOODS_INFO +
                "(_ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL," +
                " NAME VARCHAR NOT NULL," +
                " DESCRIPTION VARCHAR NOT NULL," +
                " PRICE FLOAT NOT NULL," +
                " PIC_PATH VARCHAR NOT NULL);";
        db.execSQL(sql);
        // 创建购物车信息表
        sql = "CREATE TABLE IF NOT EXISTS " + TABLE_CART_INFO +
                "(_ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL," +
                " GOODS_ID INTEGER NOT NULL," +
                " COUNT INTEGER NOT NULL);";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    // 添加多条商品信息
    public void insertGoodsInfos(List<GoodsInfo> list) {
        // 插入多条记录，要么全部成功，要么全部失败
        try {
            mWDB.beginTransaction();
            for (GoodsInfo info : list) {
                ContentValues values = new ContentValues();
                values.put("name", info.name);
                values.put("description", info.description);
                values.put("price", info.price);
                values.put("pic_path", info.picPath);
                mWDB.insert(TABLE_GOODS_INFO, null, values);
            }
            mWDB.setTransactionSuccessful();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            mWDB.endTransaction();
        }
    }

    // 查询所有的商品信息
    public List<GoodsInfo> queryAllGoodsInfo() {
        String sql = "select * from " + TABLE_GOODS_INFO;
        List<GoodsInfo> list = new ArrayList<>();
        Cursor cursor = mRDB.rawQuery(sql, null);
        while (cursor.moveToNext()) {
            GoodsInfo 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);
            list.add(info);
        }
        return list;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/ll_item"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:background="@color/white"
    android:gravity="center"
    android:orientation="vertical"
    xmlns:tools="http://schemas.android.com/tools">

    <TextView
        android:id="@+id/tv_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="@color/black"
        android:textSize="17sp"
        tools:text="小米手机"/>

    <ImageView
        android:id="@+id/iv_thumb"
        android:layout_width="180dp"
        android:layout_height="150dp"
        android:scaleType="fitCenter"
        tools:src="@drawable/xiaomi"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="45dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_price"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="2"
            android:gravity="center"
            android:textColor="@color/red"
            android:textSize="15sp"
            tools:text="20"/>

        <Button
            android:id="@+id/btn_add"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="3"
            android:gravity="center"
            android:text="加入购物车"
            android:textColor="@color/black"
            android:textSize="15sp"/>

    </LinearLayout>
</LinearLayout>

<style name="Theme.MyApplication" parent="Theme.MaterialComponents.DayNight.NoActionBar.Bridge">