CS_BS/EatWhatActivity.java

package com.example.WhatMeal;

import android.content.ContentValues;
import android.content.Intent;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MenuActivity extends AppCompatActivity implements View.OnClickListener
{
    MyHelper myHelper;
    private Button back;
    private EditText mEtName;
    private EditText mEtStore;
    private TextView mShow;
    private Button mBtnAdd;
    private Button mBtnQuery;
    private Button mBtnUpdate;
    private Button mBtnDelete;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_menu);
        myHelper = new com.example.WhatMeal.MenuActivity.MyHelper(this);
        back = (Button) findViewById(R.id.back);
        back.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                Intent intent = new Intent(MenuActivity.this, MainActivity.class);
                startActivity(intent);
            }
        });
        init();//初始化控件
    }
    private void init()
    {
        mEtName = (EditText) findViewById(R.id.et_name);
        mEtStore = (EditText) findViewById(R.id.et_store);
        mShow = (TextView) findViewById(R.id.show);
        mBtnAdd = (Button) findViewById(R.id.btn_add);
        mBtnQuery = (Button) findViewById(R.id.btn_query);
        mBtnUpdate = (Button) findViewById(R.id.btn_update);
        mBtnDelete = (Button) findViewById(R.id.btn_delete);
        mBtnAdd.setOnClickListener(this);
        mBtnQuery.setOnClickListener(this);
        mBtnUpdate.setOnClickListener(this);
        mBtnDelete.setOnClickListener(this);
    }
    @Override
    public void onClick(View v)
    {
        String name;
        String store;
        SQLiteDatabase db;
        ContentValues values;
        switch (v.getId())
        {
            case R.id.btn_add: //添加数据
                name = mEtName.getText().toString();
                store = mEtStore.getText().toString();
                db = myHelper.getWritableDatabase();//获取可读写SQLiteDatabase对象
                values = new ContentValues();       //创建ContentValue对象
                values.put("foodname", name);       //将数据添加到ContentValues对象
                values.put("foodstore", store);
                db.insert("information", "name", values);
                Toast.makeText(this, "信息已添加", Toast.LENGTH_SHORT).show();
                db.close();
                break;
            case R.id.btn_query: //查询数据
                db = myHelper.getReadableDatabase();
                Cursor cursor = db.query("information", null, null, null, null, null, null);
                if(cursor.getCount() == 0)
                {
                    mShow.setText("");
                    Toast.makeText(this, "没有数据", Toast.LENGTH_SHORT).show();
                }
                else
                {
                    cursor.moveToFirst();
                    mShow.setText("菜名：" + cursor.getString(1) + "；店名：" + cursor.getString(2));
                }
                while (cursor.moveToNext())
                {
                    mShow.append("\n" + "菜名：" + cursor.getString(1) + "；店名：" + cursor.getString(2));
                }
                cursor.close();
                db.close();
                break;
            case R.id.btn_update: //修改数据
                db = myHelper.getWritableDatabase();
                values = new ContentValues();
                values.put("foodstore", store = mEtStore.getText().toString());
                db.update("information", values, "foodname=?", new String[]{mEtName.getText().toString()});
                Toast.makeText(this, "信息已修改", Toast.LENGTH_SHORT).show();
                db.close();
                break;
            case R.id.btn_delete: //删除数据
                db = myHelper.getWritableDatabase();
                db.delete("information", null, null);
                Toast.makeText(this, "信息已删除", Toast.LENGTH_SHORT).show();
                mShow.setText("");
                db.close();
                break;
        }
    }

    static class MyHelper extends SQLiteOpenHelper
    {
        public MyHelper(Context context)    //数据库第一次被创建时调用方法
        {
            super(context, "EatWhat.db", null, 2);
        }
        @Override
        public void onCreate(SQLiteDatabase db) //初始化数据库的表结构，执行一条建表的SQL语句
        {
            db.execSQL("CREATE TABLE information(_id INTEGER PRIMARY KEY AUTOINCREMENT, foodname VARCHAR(40), foodstore VARCHAR(40))");
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {} //当数据库的版本号增加时调用
    }
}