android - 是否可以将内部数据库移动到 SDCard？

Question

随着我应用中数据库的增长，它需要越来越多的内部手机空间。数据库中没有任何敏感/隐私数据，因此我有兴趣将其移至 SD 卡。

我正在使用 SQLiteOpenHelper 来协助数据库工作。据我了解，您不能将其用于 SD 卡上的数据库访问，因为您无法定义数据库路径。但是，Internet 上有一些(非常糟糕的)示例建议您可以覆盖此限制。但是，我从来没有编译过这些代码示例之一。

这可能吗？如果是这样——如何!请注意，Froyo 的“SD 卡上的应用程序”功能将不起作用，因为它不会移动内部文件。

Answer 1

只需使用:

SQLiteDatabase.openDatabase(DB_FULL_PATH, null, SQLiteDatabase.OPEN_READONLY);

DB_FULL_PATH 可以是你的 sdcard 的路径，比如/sdcard/mydatabase.db

编辑:

这就是我在我的应用程序中调用的访问数据库的方法....

private static DBUtil dbHelper = null;

public void openDatabase() {
    if(dbHelper == null) {
        dbHelper = new DBUtil(this.context);
        dbHelper.openDataBase(SQLiteDatabase.OPEN_READWRITE);
    }
}
public void closeDatabase() {
    if(dbHelper != null) {
        dbHelper.close();
        dbHelper = null;
    }
}

...这是我正在使用的数据库助手类，它实际上扩展了 SQLiteOpenHelper，因此您仍然可以从该类中获得所需的一切。

package com.myapp.android.db;

import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import com.myapp.android.MyApp;

import java.io.IOException;

/**
 * Standard database utility class.
 * 
 * TODO: Refactor.
 */
public class DBUtil extends SQLiteOpenHelper {

    /**
     * Database directory.
     * 
     * <p>
     * Example: "/sdcard/myapp/db/"
     * </p>
     */
    public static String DB_DIRECTORY = null;

    /**
     * Name of the database file.
     * 
     * <p>
     * Example: "mydatabase.db"
     * </p>
     * 
     */
    public static String DB_NAME = null;

    /**
     * Full absolute path of the database.
     * 
     * <p>
     * Example: "/sdcard/myapp/db/mydatabase.db"
     * </p>
     */
    public static String DB_FULL_PATH = null;
    static {
        DB_DIRECTORY = MyApp.DATA_REPOSITORY_URI + "/myapp/db/";
        DB_NAME = "mydatabase.db";
        DB_FULL_PATH = DB_DIRECTORY + DB_NAME;
    }

    private SQLiteDatabase myDataBase;

    /**
     * Constructor Takes and keeps a reference of the passed context in order to
     * access to the application assets and resources.
     * 
     * @param context
     */
    public DBUtil(Context context) {
        super(context, DB_NAME, null, 1);

        try {
            this.createDataBase();
        } catch (IOException ioe) {
            throw new Error("Unable to create database");
        }
    }

    /**
     * Creates a empty database on the system and rewrites it with your own
     * database.
     * */
    public void createDataBase() throws IOException {        
        if (!checkDataBase()) this.getWritableDatabase();
    }

    /**
     * Check if the database already exist to avoid re-copying the file each
     * time you open the application.
     * 
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            checkDB = SQLiteDatabase.openDatabase(DB_FULL_PATH, null,
                    SQLiteDatabase.OPEN_READONLY);
        } catch (SQLiteException e) {
            // database does't exist yet.
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null ? true : false;
    }

    public void openDataBase(int mode) throws SQLException {        
        try {
            myDataBase = SQLiteDatabase.openDatabase(DB_FULL_PATH, null, mode);
        } catch(IllegalStateException e) {
            // Sometimes, esp. after application upgrade, the database will be non-closed, raising a IllegalStateException
            // below. Try to avoid by simply opening it again.
            Log.d(MyApp.APP, "Database non-closed. Reopening.");
            myDataBase = SQLiteDatabase.openDatabase(DB_FULL_PATH, null, mode);
        }
    }

    public void openDataBase() throws SQLException {
        openDataBase(SQLiteDatabase.OPEN_READWRITE);
    }

    public SQLiteDatabase getDb() {
        return myDataBase;
    }

    @Override
    public synchronized void close() {
        if (myDataBase != null)
            myDataBase.close();
        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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

}