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);