[Android]SQLite的使用

Android 数据存储提供了四种存储方式:

  • Shared Preferences

      使用键值对(Map(key, value))来存储数据 
  • Internal Storage

      内部存储,存储在设备内存的 私人数据 
  • External Storage

      外部存储,存储在外部设备的 公共数据 
  • SQLite Databases

      存储在关系型数据库;SQLite 是类似MySQL 的关系型数据库,因为其体较小,功能全,被运用在了大多嵌入式设备 

    Network Connection

SQLite 简介

非常小的关系型数据库

SQLiteOpenHelper

CRUD(增删改查)


import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;


public class SimpleActivity extends Activity {

    private static final String INFO = "SimpleActivity";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.simple_layout);
        Log.i(INFO, INFO);

        SQLiteDatabase db = openOrCreateDatabase("simple.db", Context.MODE_PRIVATE, null);
        db.execSQL("DROP TABLE IF EXISTS Person");

        // 创建表
        db.execSQL("CREATE TABLE Person ("
                + "  id INTEGER PRIMARY KEY AUTOINCREMENT,"
                + "  name varchar(30),"
                + "  age SMALLINT"
                + ")");
        Log.d(INFO, "Create Table Successful");

        Person person = new Person();
        person.name = "Tikitoo";
        person.age = 23;
        // 插入数据
        db.execSQL("INSERT INTO Person VALUES(NULL , ?, ?)", new Object[]{person.name, person.age});
        Log.d(INFO, "Insert Successful");

        person.name = "Davin";
        person.age = 30;
        ContentValues cv = new ContentValues();
        cv.put("name", person.name);
        cv.put("age", person.age);
        // 插入ContentValue 中的数据
        db.insert("Person", null, cv);
        Log.d(INFO, "ContentValues Insert Successful");

        cv = new ContentValues();
        cv.put("age", 35);
        // 更新数据
        db.update("Person", cv, "name = ?", new String[]{"Davin"});
        Log.d(INFO, "Update Successful");

        Cursor cursor = db.rawQuery("SELECT * FROM Person", null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            int age = cursor.getInt(cursor.getColumnIndex("age"));
            Log.d("INFO", id + name + age);
        }
        Log.d(INFO, "Query Successful");

        cursor.close();

        db.delete("Person", "age < ?", new String[]{"25"});
        Log.d(INFO, "Delete Successful");

        db.close();

        // deleteDatabase("tikitoo_sqlite.db");
    }
}

参考:

Android SQLite Database Tutorial
Android中SQLite应用详解 – scott’s blog – 博客频道 – CSDN.NET

问题总结

使用SQLite 调试工具ADB(adb)

(android:adb环境变量的配置)[http://blog.csdn.net/huangbiao86/article/details/6664779]
使用ADB 工具查看adb shell

cd data,ls 出现错误,这是,输入su 回车即可,会请求访问权限,在手机同意一下;
adb opendir failed ,permission denied

当然Android 对于SQLite 处理封装的对象 SQLiteOpenHelper 来返回 SQLiteDatabase 对象来实现增删改查
我们再开发的时候,不能像上面写得那么简单,需要对封装一个子类,提供SQLiteOpenHelper 对象;

封装的SQLiteOpenHelper 对象

package com.tikitoo.android.sqlite.util;

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

/**
 * Created by Tikitoo1 on 2014/11/12.
 */
public class DBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "test.db";
    private static final int DATABASE_VERSION = 1;

    public DBHelper(Context context) {
        // 设置SQLiteDatabase.CursorFactory 为null
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // 数据库第一次创建被调用
    @Override
    public void onCreate(SQLiteDatabase db) {
        // 初始化创建一个表
        db.execSQL("CREATE TABLE IF NOT EXISTS Person"
                + "(id INTEGER PRIMARY KEY AUTOINCREMENT, name varchar(30), age  SMALLINT");
    }

    // 如果数据库版本改变,则会调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 新增一个字段
        db.execSQL("ALTER TABLE Person ADD COLUMN other STRING");
    }
}

DatabaseSQLite 对象实现对数据库的增删改查


import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

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


public class DBManager {

    private static final String INFO = DBManager.class.toString();
    private DBHelper helper;
    private SQLiteDatabase db;

    public DBManager(Context context) {
        helper = new DBHelper(context);
        db = helper.getWritableDatabase();
        // helper.getReadableDatabase();
    }

    // 新增一条数据,将数据存在Person 对象,在放在List 集合中,遍历集合,可以实现多条数据插入;
    public void add(List<Person> persons) {
        db.beginTransaction();

        try {
            for (Person person : persons) {
                db.execSQL("INSERT INTO Person VALUES(NULL, ?, ?, ?)",
                        new Object[]{person.name, person.age, person.info});
            }

            // 设置事物
            db.setTransactionSuccessful();
        } finally {
            // 结束事物
            db.endTransaction();
        }
    }

    // 更新一条数据,通过name 来修改age
    public void update(Person person) {
        ContentValues cv = new ContentValues();
        cv.put("age", person.age);
        cv.put("info", person.info);
        // 参数,(表名, ContentValues 对象, where 条件,where 条件对应的值)
        db.update("Person",cv, "name = ?", new String[]{person.name});
    }

    public void delete(Person person) {
        db.delete("Person", "age >= ?", new String[]{"" + person.age});// String.valueOf(person.age);
    }

    public List<Person> person() {
        List<Person> lists = new ArrayList<Person>();

        // 使用rawQuery() 方法,返回游标对象,遍历出数据库的数据
        Cursor cursor = db.rawQuery("SELECT * FROM Person", null);
        while (cursor.moveToNext()) {
            int _id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            int age = cursor.getInt(cursor.getColumnIndex("age"));
            String info = cursor.getString(cursor.getColumnIndex("info"));

            Log.i(INFO, new Person(_id, name, age, info).toString());
        }
        return lists;
    }

    // 关闭数据库
    public void closeDB() {
        db.close();
    }
}

对了还有将数据表使用JavaBean 处理,将数据存储在Person 对象,比较方便

public class Person {
    public int _id;     // id,唯一标识
    public String name; // 姓名
    public int age;     // 年龄
    public String info; // 备注信息

    public Person() {
    }

    public Person(String name, int age, String info) {
        this.name = name;
        this.age = age;
        this.info = info;
    }

    public Person(int _id, String name, int age, String info) {
        this._id = _id;
        this.name = name;
        this.age = age;
        this.info = info;
    }

    // 重写toString() 方法
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("Person[ ");
        sb.append("name = " + this.name);
       // sb.append("; id = " + _id);
        sb.append("; age = " + this.age);
        sb.append("; info = " + this.info);
        sb.append(" ]");
        return sb.toString();
    }
}

getReadableDatabase() 和getWritableDatabase() 方法的区别:

getReadableDatabase:

首先判断数据库实例是否是打开状态,
如果是,则打开一个可读写的数据库实例;
如果遇到磁盘已满,获取失败,再以可读模式打开数据库,返回数据库实例

getWritableDatabase:

如果不为空,已经打开,并不是以只读模式打开的,
如果mDatabase 不为空则加锁,然后创建或打开新的数据库实例,比较版本,为数据库设置新的版本号,最后把不为空的mDatabase 解锁,把新创建的数据库实例赋值给 mDatabase,并返回新的实例;

总结

所以,如果不遇到磁盘已满的情况下,两个方式返回的数据库实例是一样的,如果担心这种方式发生,先调用 getWritableDatabase 方法,
如果异常,则在调用 getReadableDatabase ,当然这个时候的数据库实例是只读的

    原文作者:sqlite
    原文地址: https://www.cnblogs.com/zhousysu/p/5483874.html
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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