android 简单书库操作 SQLite使用

Sqlite数据库是一种轻量级数据库，它具备跨平台，多语言操作等优点，它广泛用于包括浏览器、IOS，Android以及一些便携需求的小型web应用系统。它具备占用资源低，处理速度快等优点。

1.首先定义一个SQLiteOpenHelper帮助类

SQLiteOpenHelper是SQLiteDatabase的一个帮助类，主要用于操作数据库和数据库升级，一般需要自定义个DBHelper类来继承SQLiteOpenHelper

定义了两条sql语句，用于创建两个表格

package com.nxm.sqlitedemo;

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

/**
 * @Auther: muzi102
 * @Date: 2018/5/2 15:12 27
 * @Describe: the infor of the class
 */
public class MyDatabaseHelper extends SQLiteOpenHelper {
    private Context context;
    public static final String CREATE_BOOK = "create table Book ("
            + "id integer primary key autoincrement, "
            + "author text, "
            + "price real, "
            + "pages integer, "
            + "name text)";

    public static final String CREATE_CATEGORY = "create table Category ("
            + "id integer primary key autoincrement, "
            + "category_name text, "
            + "category_code integer)";

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
        this.context = context;
    }


    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_CATEGORY);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists Book");
        db.execSQL("drop table if exists Category");
        onCreate(db);
    }
}

2.然后在使用到的地方new一个

    private MyDatabaseHelper dbHelper = new MyDatabaseHelper(this, "BookStore.db", null,1);

3.调用 dbHelper.getWritableDatabase();方法出发onCreate方法创建数据库（数据库不存在则创建）

dbHelper.getWritableDatabase();

4.对数据库插入数据操作

 SQLiteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                // 开始组装第一条数据
                values.put("name", "The Da Vinci Code");
                values.put("author", "Dan Brown");
                values.put("pages", 454);
                values.put("price", 16.96);
                db.insert("Book", null, values); // 插入第一条数据
                values.clear();
                // 开始组装第二条数据
                values.put("name", "The Lost Symbol");
                values.put("author", "Dan Brown");
                values.put("pages", 510);
                values.put("price", 19.95);
                db.insert("Book", null, values); // 插入第二条数据

5.修改数据库数据

 SQLiteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("price", 10.99);
                db.update("Book", values, "name = ?", new String[] { "The Da Vinci Code" });

6.查询数据库内容

SQLiteDatabase db = dbHelper.getWritableDatabase();
                // 查询Book表中所有的数据
                Cursor cursor = db.query("Book", null, null, null, null, null, null);
                if (cursor.moveToFirst()) {
                    do {
                        // 遍历Cursor对象，取出数据并打印
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        String author = cursor.getString(cursor.getColumnIndex("author"));
                        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                        double price = cursor.getDouble(cursor.getColumnIndex("price"));
                        Log.d("MainActivity", "book name is " + name);
                        Log.d("MainActivity", "book author is " + author);
                        Log.d("MainActivity", "book pages is " + pages);
                        Log.d("MainActivity", "book price is " + price);
                    } while (cursor.moveToNext());
                }
                cursor.close();