文件读写、SharePreferences、SQLite

文件写：

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

文件读：

    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();

SharedPreference:

        SharedPreferences.Editor editor = getSharedPreferences("data",MODE_PRIVATE).edit();        editor.putString("name","bob");        editor.apply();

        SharedPreferences pref = getSharedPreferences("data",MODE_PRIVATE);        String name = pref.getString("name","");        Log.d("MainAcitivity","name is " + name);   

SQLite:

public class MyDatabaseHelper extends SQLiteOpenHelper {    public static final String CREATE_BOOK = "create table Book(id integer primary key autoincrement,author 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);    }    @Override    public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){            }}

建表：

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

添加一个新表：

public class MyDatabaseHelper extends SQLiteOpenHelper {    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,catogory_name text,category_code integer)";    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);        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);    }}

dbHelper = new MyDatabaseHelper(this,"BookStore.db",null,2);

添加数据：

SQLiteDatabase db = dbHelper.getWritableDatabase();ContentValues values = new ContentValues();values.put("name","bob");values.put("author","bob author");values.put("pages",458);values.put("price",666);db.insert("Book",null,values);

更新：

SQLiteDatabase db = dbHelper.getWritableDatabase();ContentValues values = new ContentValues();values.put("price",233);db.update("Book",values,"name=?",new String[]{"bob"});

删除：

QLiteDatabase db = dbHelper.getWritableDatabase();db.delete("Book","pages > ?",new String[]{"100"});

查询：

SQLiteDatabase db = dbHelper.getWritableDatabase();Cursor cursor = db.query("Book",null,null,null,null,null,null);if (cursor.moveToFirst()) {    do {        String name = cursor.getString(cursor.getColumnIndex("name"));        Log.d("MainActivity",name);    }while (cursor.moveToNext());}cursor.close();

用SQL语句CURD操作：

db.execSQL("insert into Book(name,author,pages,price)values(?,?,?,?)",new String[]{"The Da","bob","458","233"});

db.execSQL("update Book set price = ? where name = ?",new String[]{"666","The Da"});

db.execSQL("delete from Book where pages > ?",new String[]{"233"});

db.rawQuery("select * from Book",null);