android persist怎樣恢復數據

在Android中，持久化數據通常是通過SharedPreferences、文件存儲或數據庫（如SQLite）來實現的。要恢復數據，您需要根據您選擇的數據存儲方式來進行操作。以下是一些常見的數據存儲方式和恢復數據的示例：

1. SharedPreferences：

存儲數據：

SharedPreferences sharedPreferences = getSharedPreferences("myPreferences", MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("key", "value");
editor.apply();

恢復數據：

SharedPreferences sharedPreferences = getSharedPreferences("myPreferences", MODE_PRIVATE);
String value = sharedPreferences.getString("key", "default_value");

2. 文件存儲：

存儲數據（將數據寫入文件）：

FileOutputStream outputStream = new FileOutputStream("data.txt");
outputStream.write("data".getBytes());
outputStream.close();

恢復數據（從文件讀取數據）：

FileInputStream inputStream = new FileInputStream("data.txt");
byte[] dataBytes = new byte[(int) new File("data.txt").length()];
inputStream.read(dataBytes);
inputStream.close();
String data = new String(dataBytes);

3. SQLite數據庫：

首先，創建一個SQLiteOpenHelper類來管理數據庫的創建和版本更新：

public class MyDatabaseHelper extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "myDatabase.db";
    public static final int DATABASE_VERSION = 1;
    public static final String TABLE_NAME = "myTable";
    public static final String COLUMN_ID = "id";
    public static final String COLUMN_DATA = "data";

    public MyDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TABLE_NAME + " (id INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_DATA + " TEXT)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

存儲數據（將數據插入到數據庫）：

MyDatabaseHelper dbHelper = new MyDatabaseHelper(context);
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(MyDatabaseHelper.COLUMN_DATA, "data");
db.insert(MyDatabaseHelper.TABLE_NAME, null, contentValues);
db.close();

恢復數據（從數據庫讀取數據）：

MyDatabaseHelper dbHelper = new MyDatabaseHelper(context);
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = db.query(MyDatabaseHelper.TABLE_NAME, new String[]{MyDatabaseHelper.COLUMN_DATA}, null, null, null, null, null);
if (cursor.moveToFirst()) {
    String data = cursor.getString(cursor.getColumnIndex(MyDatabaseHelper.COLUMN_DATA));
}
cursor.close();
db.close();

根據您的需求選擇合適的數據存儲方式，并按照上述示例進行數據的存儲和恢復。