Android 数据持久化主要有三种：
文件，SharePreference, 数据库
文件存储
不对存储的文件进行任何格式化的处理，所有数据都是直接存入文件中，因此比较适合保存一些简单的文本数据和二进制数据
- 存入读取：
FileOutputStream out = null;
BufferedWriter writer = null;
try {
out = openFileOutput("data", Context.MODE_PRIVATE);
/*主要有两种模式：
1.MODE_PRIVATE:当指定同名文件时，自动覆盖
2.MODE_APPEND：已存在就追加
*/
writer = new BufferedWriter(new OutputStreamWriter(out));//得到一个OutputStreamwriter对象
//再构建一个bufferedWriter
writer.write(inputText);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (writer != null) {
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public String load() {
FileInputStream in = null;
BufferedReader reader = null;
StringBuilder content = new StringBuilder();
try {
in = openFileInput("data");
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = reader.readLine()) != null) {
content.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return content.toString();
}
- java知识小补点
String,StringBuffer,StringBuilder区别：
String 利用字符数组保存数据，源码中有final修饰，因而实际上是不可变的
当String a = "b"+"c"时，实际上创建了两个对象
而StringBuffer和StringBuilder都只创建一个实例
SringBuffer 线程安全，而StringBuider线程不安全
三者的效率，String < StringBuffer < StringBuilder
SharedPreference 存储
这是一种应用私有的，利用键值对存储数据的方式，支持对不同类型的数据类型进行储存，存为xml格式，方便小巧效率高
存入：
SharedPreferences.Editor editor = getSharedPreferences("data", MODE_PRIVATE).edit();
editor.putString("name", "Tom");
editor.putInt("age", 28);
editor.putBoolean("married", false);
editor.apply();
取出：
SharedPreferences pref = getSharedPreferences("data", MODE_PRIVATE);
String name = pref.getString("name", "");
int age = pref.getInt("age", 0);
boolean married = pref.getBoolean("married", false);
这是context类中的getSharedPreferences（）方法的模式
2.Activity类中的getPreferences()方法
3.PrefenceMangager类中的getDefaultSharedPreferences
e.g.
读取
SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(WeatherActivity.this);
存入
SharedPreferences.Editor editor =PreferenceManager.getDefaultSharedPreferences(WeatherActivity.this).edit();
editor.putString("weather",mresponse);
editor.apply();
- SQLite数据库
SQLite 是一个 Android 自带的轻量型的数据库。 - 利用数据库的 DBHelper 建库建表
- e.g.
class AreaDBHelper extends SQLiteOpenHelper {
//定义 private static 语句 用于直观呈现数据库所需要的参数
private static final int DB_VERSION = 1;
private static final String DB_NAME = "area.db";
private static final String PROVINCE_NAME = "province";
private static final String CITY_NAME = "city";
private static final String COUNTY_NAME = "county";
AreaDBHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
//构造方法需要提供四个参数，context, 库名，cursor，版本号
}
//建表建库，sql 语句要特别留意！
@Override
public void onCreate(SQLiteDatabase db) {
String sql1 = "create table if not exists "
+ PROVINCE_NAME
+ " (Id integer primary key autoincrement,"
+ "ProvinceName text,"
+ "ProvinceId integer)";
String sql2 = "create table if not exists "
+ CITY_NAME
+ " (Id integer primary key autoincrement,"
+ "CityName text,"
+"CityId integer,"
+"ProvinceId integer)";
String sql3 = "create table if not exists "
+COUNTY_NAME
+ " (Id integer primary key autoincrement,"
+ "ProvinceId integer,"
+ "CityId integer,"
+ "CountyName text,"
+ "WeatherId text)";
db.execSQL(sql1);
db.execSQL(sql2);
db.execSQL(sql3);
}
//数据库的升级方法
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String sql1 = "DROP TABLE IF EXISTS" + PROVINCE_NAME;
String sql2 = "DROP TABLE IF EXISTS" + CITY_NAME;
String sql3 = "DROP TABLE IF EXISTS" + COUNTY_NAME;
db.execSQL(sql1);
db.execSQL(sql2);
db.execSQL(sql3);
onCreate(db);
}
}
- 利用 DBDao 类对有关数据库进行操作
public class DBDao {
private Context mcontext;
private AreaDBHelper areaDBHelper;
/*
*自定义构造器的做法，将传入的 context 赋值给mcontext
*/
public DBDao(Context context){
this.mcontext = context;
areaDBHelper = new AreaDBHelper(context);
}
/**
* 将省级列表存入数据库
* @param provinceList
*/
public void initProvinceTable(List<Province> provinceList){
SQLiteDatabase db = areaDBHelper.getWritableDatabase();
ContentValues values = new ContentValues();
for(Province province:provinceList){
values.put("ProvinceName",province.getProvinceName());
values.put("ProvinceId",province.getProvinceCode());
db.insert("province",null,values);
values.clear();
}
db.close();
}
/**
*在数据库中查询省级
*/
public List<Province> queryProvince(){
List<Province> provinceList = new ArrayList<>();
SQLiteDatabase db = areaDBHelper.getWritableDatabase();
Cursor cursor = db.query("province",null,null,null,null,null,null);
if(cursor.moveToFirst()){
do{
String provinceName = cursor.getString(cursor.getColumnIndex("ProvinceName"));
int provinceCode = cursor.getInt(cursor.getColumnIndex("ProvinceId"));
Province province = new Province();
province.setProvinceCode(provinceCode);
province.setProvinceName(provinceName);
provinceList.add(province);
}while (cursor.moveToNext());
}
cursor.close();
db.close();
return provinceList;
}
}
}
- 数据库是耗资源的操作，应避免频繁访问，用完记得关闭连接
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