[Android][第一行代码][第 6 章 数据存储]

01. 持久化简介

02. 文件存储

Context

openFileOutput()

Context.MODE_PRIVATE

Context.MODE_APPEND

Context

openFileInput()

/**
* 保存数据到内部存储文件
*
* @param fileName 文件名称
* @param saveData 写入的数据
*/
private void saveToFile(String fileName, String saveData) {
FileOutputStream fileOutputStream = null;
BufferedWriter bufferedWriter = null;
try {
fileOutputStream = this.openFileOutput(fileName, Context.MODE_APPEND);// [/data/data/com.just.first/files]
bufferedWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
bufferedWriter.write(saveData);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (bufferedWriter != null) {
bufferedWriter.close();
}
if (fileOutputStream != null) {
fileOutputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

/**
* 从内部存储文件中读取数据
*
* @param fileName 文件名称
* @return 文件内容
*/
private String loadFromFile(String fileName) {
FileInputStream fileInputStream = null;
BufferedReader bufferedReader = null;
StringBuilder dataContent = new StringBuilder();
try {
fileInputStream = this.openFileInput(fileName);
bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));
String line = "";
while ((line = bufferedReader.readLine()) != null) {
dataContent.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (bufferedReader != null) {
bufferedReader.close();
}
if (fileInputStream != null) {
fileInputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return dataContent.toString();
}

03. SharedPreferences

SharedPreferences

多种

数据类型

/data/data/主包名/shared_prefs

xml

sharedPreferences

Context

getSharedPreferences(String name, int mode)

Activity

getPreferences(int mode)

getLocalClassName()

PreferenceManager

getDefaultSharedPreferences(Context context)

context.getPackageName() + "_preferences"

SharedPreferences.Editor

Editor

Editor

apply()

/**
* 将数据保存到 SharedPreferences
*
* @param fileName 文件名
* @param keyWord  键
* @param saveData 值
*/
private void saveToSharedPreferences(String fileName, String keyWord, String saveData) {
SharedPreferences sharedPreferences = this.getSharedPreferences(fileName, MODE_APPEND);
SharedPreferences.Editor edit = sharedPreferences.edit();
edit.putString(keyWord, saveData);
edit.apply();
}

/**
* 从 SharedPreferences 加载数据
*
* @param fileName 文件名
* @param keyWord  键
* @return 值
*/
private String loadFromSharedPreferences(String fileName, String keyWord) {
SharedPreferences sharedPreferences = this.getSharedPreferences(fileName, MODE_APPEND);
return sharedPreferences.getString(keyWord, null);// 默认值
}

04. SQLite 数据库

SQLite

SQLiteOpenHelper

SQLiteOpenHelper

/**
* SQLiteOpenHelper 实现数据库创建与升级
*
* @author JustDo23
*/
public class BookOpenHelper extends SQLiteOpenHelper {

/**
* 构造方法[必须实现]
*
* @param context 上下文
* @param name    数据库名称[带上后缀 .db]
* @param factory 工厂[允许数据查询使用自定义 Cursor][一般传 null]
* @param version 版本[整型]
*/
public BookOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, "BookStore" + ".db", null, 1);
}

/**
* 创建数据表方法[必须实现]
*
* @param db 数据库操作对象
*/
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table Book ( "
+ "id integer primary key autoincrement" + ", "
+ "author text" + ", "
+ "price real" + ", "
+ "pages integer" + ", "
+ "name text"
+ ")";
db.execSQL(sql);// 执行 SQL 语句
}

/**
* 数据库升级方法[必须实现]
*
* @param db         数据库操作对象
* @param oldVersion 旧的版本号
* @param newVersion 新的版本号
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

}

/data/data/主包名/databases

注意：

integer

real

text

blob

primary key

autoincrement

SQLiteOpenHelper

SQLiteOpenHelper

getReadableDatabase()

getWritableDatabase()

getReadableDatabase()

getWritableDatabase()

$ adb shell

$ sqlite3 BookStore.db

$ .table

android_metadata

$ .schema

$ .exit
$ .quit

05. 数据库操作

/**
* 数据库升级方法
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists Book");// 删除原来的表
onCreate(db);// 重新进行创建
}

CRUD

C

Create

insert

R

Retrieve

select

U

Update

update

D

Delete

delete

SQLiteDatabase

insert(String table, String nullColumnHack, ContentValues values)

public void insert() {
SQLiteDatabase writableDatabase = bookOpenHelper.getWritableDatabase();// 获取数据操作对象
ContentValues contentValues = new ContentValues();// 键值对集合
contentValues.put("name", "FirstLine");// 列名-数据
contentValues.put("author", "Guo");
contentValues.put("pages", "570");
contentValues.put("price", 79.0);
writableDatabase.insert("Book", null, contentValues);// 指定表名添加
}

$ select * from Book;

SQLiteDatabase

update(String table, ContentValues values, String whereClause, String[] whereArgs)

?

public void update() {
SQLiteDatabase writableDatabase = bookOpenHelper.getWritableDatabase();// 获取数据操作对象
ContentValues contentValues = new ContentValues();// 键值对集合
contentValues.put("price", 99.9);
writableDatabase.update("Book", contentValues, "name = ?", new String[]{"FirstLine"});
}

SQLiteDatabase

delete(String table, String whereClause, String[] whereArgs)

public void delete() {
SQLiteDatabase writableDatabase = bookOpenHelper.getWritableDatabase();// 获取数据操作对象
writableDatabase.delete("Book", "name = ?", new String[]{"FirstLine"});
}

SQL

Structured Query Language

结构化查询语言

SQLiteDatabase

query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)

query()

public void query() {
SQLiteDatabase readableDatabase = bookOpenHelper.getReadableDatabase();// 获取数据操作对象
Cursor cursor = readableDatabase.query("Book", null, null, null, null, null, null);// 查询获得游标
if (cursor.moveToFirst()) {// 是否可以移动位置
do {
String author = cursor.getString(cursor.getColumnIndex("author"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String pages = cursor.getString(cursor.getColumnIndex("pages"));
String price = cursor.getString(cursor.getColumnIndex("price"));
LogUtils.e("Book: " + author + " -- " + name + " -- " + pages + " -- " + price);
} while (cursor.moveToNext());// 是否可以继续往下移动
}
}

writableDatabase.execSQL("insert into Book (name, author, pages, price) values (?, ?, ?, ?)", new String[]{"SecondLine", "Lin", "123", "66.6"});writableDatabase.execSQL("insert into Book (name, author, pages, price) values (?, ?, ?, ?)", new String[]{"SecondLine", "Lin", "123", "66.6"});

writableDatabase.execSQL("update Book set pages = ? where author = ?", new String[]{"333", "Lin"});writableDatabase.execSQL("update Book set pages = ? where author = ?", new String[]{"333", "Lin"});

writableDatabase.execSQL("delete from Book where pages > ?", new String[]{"10"});

readableDatabase.rawQuery("select * from Book", null);// 查询获得游标

06. LitePal 数据库

assets

litepal.xml

Application

litepal.xml

LitePal.getDatabase();// 使用 LitePal 创建数据库

DataSupport

save()

Book book = new Book();// 实例化实体类
book.save();// 使用 LitePal 插入数据

save()

model.isSaved()

true

save()

LitePal

查询 API

Book book = new Book();// 实例化实体类
book.save();// 使用 LitePal 插入数据
book.setPages("324");// 更新数据
book.save();// 对插入的数据进行更新

updateAll(String... conditions)

注意：

setToDefault(String fieldName)

Book book = new Book();// 实例化实体类
book.setPages("776");// 更新数据
book.setToDefault("price");// 设置默认值
book.updateAll("name = ? and pages = ?", "老人与海", "76");

delete()

DataSupport.deleteAll()

DataSupport.deleteAll(Book.class, "pages < ?", "400");// 指定表名及约束进行删除

DataSupport

DataSupport.findAll(Book.class);// 查询所有
DataSupport.findFirst(Book.class);// 查询第一条
DataSupport.findLast(Book.class);// 查询最后一条

DataSupport.select("name", "author", "pages")// 指定查询的列
.where("pages > ?", "400")// 指定查询的约束条件
.order("pages desc")// 指定查询结果排序
.limit(10)// 指定查询结果数量
.offset(2)// 指定查询结果偏移-抛弃前2条
.find(Book.class);// 指定查询的表名

select()

where()

order()

desc

asc

limit()

offset()

07. 小结

Java

I/O 流操作

SharedPreferences

apply()

commit()