我想提出一个问答游戏，我想使用SQLite数据库在那里我将存储300+问题，并随机选择其中之一。我做了一个研究，我知道如何创建和更新表，如何在Android应用程序添加，修改和删除行，但我不能找到一种方法，我的应用程序连接到已完成的数据库（存储在只读数据库在资源（资产）文件夹）。

I am making a quiz game and I would like to use SQLite database where I will store 300+ questions and randomly choose one of them. I made a research and I know how to create and update table, how to add, modify and delete rows within an Android app but I couldn't find a way to connect my app to an already done database (a read-only database stored in the resources(assets) folder).

你能帮帮我吗？

推荐答案

您应该从资产的文件夹中的数据库文件复制到安装的应用程序。 例如：

You should copy your DB file from assets folder to your installed application. for example:

public class DatabaseOpenHelper extends SQLiteOpenHelper {

private final static String DB_NAME = "YourDatabaseFile.sqlite";
private static String DB_PATH = "/data/data/%s/databases/";
private final String ERROR_TAG = "error";
private final static int DB_VERSION = 1;
private final int BUFFER_SIZE = 8 * 1024;
private SQLiteDatabase databaseHandle;

private final Context context;

public DatabaseOpenHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);

    this.context = context;
    DB_PATH = String.format(DB_PATH, context.getPackageName());
}

public SQLiteDatabase openDataBase() {
    try {
        String databasePath = DB_PATH + DB_NAME;
        if (databaseHandle == null) {
            createDataBase();
            databaseHandle = SQLiteDatabase.openDatabase(databasePath, null, SQLiteDatabase.OPEN_READWRITE);
        }
    }
    catch (SQLiteException e) {
        throw new IllegalStateException(context.getResources().getString(R.string.err_opening_db), e);
    }
    return databaseHandle;
}

private boolean createDataBase() {
    try {
        if (!isDataBase()) {
            this.getReadableDatabase();
            copyDataBase();
            return true;
        }
    }
    catch (SQLiteException e) {
        throw new IllegalStateException(context.getResources().getString(R.string.err_opening_db), e);
    }
    catch (IOException e){
        Log.e(ERROR_TAG, context.getResources().getString(R.string.err_close_stream), e);
    }

    return false;
}

public boolean isDataBase() {
    SQLiteDatabase verifiableDatabase = null;
    try {
        String databasePath = DB_PATH + DB_NAME;
        verifiableDatabase = SQLiteDatabase.openDatabase(databasePath, null, SQLiteDatabase.OPEN_READONLY);
        verifiableDatabase.close();
    }
    catch (SQLiteException e) {
        Log.e(ERROR_TAG, context.getResources().getString(R.string.err_opening_db), e);
        return false;
    }

    return true;
}

private void copyDataBase() throws IOException {
    InputStream externalDbStream = null;
    OutputStream localDbStream = null;
    try {
        externalDbStream = context.getAssets().open(DB_NAME);
        localDbStream = new FileOutputStream(DB_PATH+DB_NAME);

        byte[] buffer = new byte[BUFFER_SIZE];
        int bytesRead;

        while ((bytesRead = externalDbStream.read(buffer)) > 0) {
            localDbStream.write(buffer, 0, bytesRead);
        }
    }
    catch (IOException e) {
        throw new IllegalStateException(context.getResources().getString(R.string.err_copying_db), e);
    }
    finally {
        if (localDbStream != null)
            localDbStream.close();
        if (externalDbStream != null)
            externalDbStream.close();
    }
}

@Override
public void close() {
    databaseHandle.close();
}

@Override
public void onCreate(SQLiteDatabase db) {
}

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

使用： DatabaseOpenHelper dbHelper =新DatabaseOpenHelper（上下文）; SQLiteDatabase数据库= dbHelper.openDataBase（）;

Using: DatabaseOpenHelper dbHelper = new DatabaseOpenHelper(context); SQLiteDatabase database = dbHelper.openDataBase();