第一行代码——第六章：详解持久化技术

1. 文件存储：

    private void save(String text) {
        FileOutputStream out = null;
        BufferedWriter writer = null;
        try {
            out = openFileOutput("data", Context.MODE_PRIVATE);
            writer = new BufferedWriter(new OutputStreamWriter(out));
            writer.write(text);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (writer != null) {
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private String load() {
        BufferedReader reader = null;
        FileInputStream in = null;
        StringBuffer buffer = new StringBuffer();
        try {
            in = openFileInput("data");
            reader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null){
                buffer.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(reader != null){
                    reader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return buffer.toString();
    }

2. sharePreference：

与文件储存相比，这种方式更为方便

一共有三种获取sharePreference的方法：

（1）context类中的 getSharePreference

（2）activity类 的getPreference ，会自动将当前活动的类名作为文件名

（3）PreferenceManager 中的静态类 getDefaultSharePreference：接受一个context，自动以当前应用程序的包名作为文件名

保存preference        
btn_save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SharedPreferences.Editor editor = getSharedPreferences("data", MODE_PRIVATE).edit();
                editor.putString("name", "Tom");
                editor.putInt("age", 19);
                editor.putBoolean("married", false);
                editor.apply();
            }
        });
重新加载preference
        btn_restore.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SharedPreferences pref = getSharedPreferences("data", MODE_PRIVATE);
                String name = pref.getString("name","");
                int age = pref.getInt("age",0);
                boolean married = pref.getBoolean("married",false);
                Log.d(TAG,name);
                Log.d(TAG,String.valueOf(age));
                Log.d(TAG,String.valueOf(married));
            }
        });

3.SQList 数据库技术

使用adb命令查看数据库

adb shell 

su root:获取root权限

cd data/data/package Name/databases

sqlite3 BookStore.db

.table

.schema

(1) 创建数据库

      创建MyDatabaseHelper 继承 SQLiteOpenHelper

      a.实现其方法

      b.定义sql语句，在OnCreate中创建表:

           db.execSQL(sql);

public class MyDatabaseHelper extends SQLiteOpenHelper {

    public static String CREATE_BOOK = "Create table Book(" +
            "id integer primary key autoincrement," +
            "anther text," +
            "price real," +
            "pages integer," +
            "name text )";

    private Context mContext;

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK);
        Toast.makeText(mContext,"Database create succeeded",Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

  c.在MainActivity中 使用MyOpenHelper，helper

（2）更新数据库

       onUpdate(){ } 在创建helper时的版本号决定是否调用这个方法。注意，onCreate方法只能调用一次。

（3）CRUD 增删改查

       

4. 一个开源库 LitePal

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_create:
                Connector.getDatabase();
                break;
            case R.id.btn_insert:
                Book book = new Book();
                book.setAuthor("zxr");
                book.setPrice(25.5);
                book.save();
                break;
            case R.id.btn_update:
                Book book = new Book();
                book.setPrice(99.9);
                book.setAuthor("zxr");
                book.updateAll("name = ? and auther = ?", "Story", "zxr");
                //book.update(2);
                break;
            case R.id.btn_delete:
                LitePal.delete(Book.class, 2);
                LitePal.deleteAll(Book.class, "price > ?", "20");
                break;
            case R.id.btn_query:
                Book first = LitePal.findFirst(Book.class);
                Book last = LitePal.findLast(Book.class);
                Book book1 = LitePal.find(Book.class, 1);
                List bookList = LitePal.findAll(Book.class);
                List bookList1 = LitePal.select("name", "auther").where("price>?", "10").order("piice").find(Book.class);
        }
    }