Question

我想创建一个测验应用程序，为此，我想我需要一个包含所有问题和答案的数据库。

我找到了关于如何在官方Android开发者网站上以编程方式创建数据库的教程，但我不认为这是我需要的，因为我不需要在应用程序时创建数据库运行，我需要一个已经编译好的数据库，我可以从中读取问题和答案。

首先，这是进行测验应用的正确方法吗？如果是的话，我怎么能这样做？

Answer 1

您将使用以下方式完成此任务。

首先使用SQlite Manager / SQlite Studio创建数据库。
将该数据库存储在Asserts文件夹中并使用以下代码

公共类DataBase扩展了SQLiteOpenHelper {

public static String DB_PATH = "/data/data/your package name here/";
public static String DB_NAME = "your database name .sqlite";
public static SQLiteDatabase _database;
private final Context myContext;
public static String apstorphe = "'";
public static String sep = ",";
private AtomicInteger mOpenCounter = new AtomicInteger();

public DataBase(Context context) throws IOException {
    super(context, DB_NAME, null, 1);
    this.myContext = context;
    createDataBase();
}

/**
 * Creates a empty database on the system and rewrites it with your own database.
 */
public void createDataBase() throws IOException {
    boolean dbExist = checkDataBase();

    if (!dbExist) {
        // By calling this method and empty database will be created into the default system path
        // of your application so we are gonna be able to overwrite that database with our database.
        try {
            copyDataBase();
        } catch (IOException e) {
            System.out.println();
        }
    }
}

/**
 * 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 {
        String myPath = DB_PATH + DB_NAME;
        checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
    } catch (SQLiteException e) {
        // database does't exist yet.
    }

    if (checkDB != null) {
        checkDB.close();
    }

    return checkDB != null ? true : false;
}

public void copyDataBase() throws IOException {

    // Open your local db as the input stream
    InputStream myInput = myContext.getAssets().open(DB_NAME);

    // Path to the just created empty db
    String outFileName = DB_PATH + DB_NAME;

    // Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);

    // transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[2048];
    int length;
    while ((length = myInput.read(buffer)) > 0) {
        myOutput.write(buffer, 0, length);
    }

    // Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();

}

public static SQLiteDatabase openDataBase() throws SQLException {
    // Open the database
    if (_database == null) {
        _database = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE | SQLiteDatabase.CREATE_IF_NECESSARY | SQLiteDatabase.NO_LOCALIZED_COLLATORS);
    } else if (!_database.isOpen()) {
        _database = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE | SQLiteDatabase.CREATE_IF_NECESSARY | SQLiteDatabase.NO_LOCALIZED_COLLATORS);
    }
    return _database;
}

public static void closedatabase() {
    if (_database != null)
        _database.close();
}

@Override
public void onCreate(SQLiteDatabase db) {

}

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

}

public static Cursor getdata(String query_str) {
    Cursor mCursor = _database.rawQuery(query_str, null);
    return mCursor;
}

public static void executeQuery(String strQuery) {

    try {
        _database.execSQL(strQuery);
    } catch (Exception e) {
        System.out.println(e.toString());
    }
}

}

Android - 如何以编程方式创建数据库

1 个答案: