java - 未在 Android 应用程序中使用 SQLite 创建表

Question

我尝试在我的应用程序中使用 sqlite 创建一个表。

这是我的代码:

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "android_api";

    // Login table name
    private static final String TABLE_LOGIN = "login";

    // Login Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_EMAIL = "email";
    private static final String KEY_UID = "uid";
    private static final String KEY_CREATED_AT = "created_at";
    private static final String KEY_TOTAL_USAGE = "total_usage";


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

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_LOGIN_TABLE = "CREATE TABLE " + TABLE_LOGIN + "("
                + KEY_ID + " INTEGER PRIMARY KEY," 
                + KEY_NAME + " TEXT,"
                + KEY_EMAIL + " TEXT UNIQUE,"
                + KEY_UID + " TEXT,"
                + KEY_CREATED_AT + " TEXT,"
                + KEY_TOTAL_USAGE + " TEXT);";
        db.execSQL(CREATE_LOGIN_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOGIN);

        // Create tables again
        onCreate(db);
    }

    /**
     * Storing user details in database
     * */
    public void addUser(String name, String email, String uid, String created_at) {
        SQLiteDatabase db = this.getWritableDatabase();


        ContentValues values = new ContentValues();
        values.put(KEY_NAME, name); // Name
        values.put(KEY_EMAIL, email); // Email
        values.put(KEY_UID, uid); // Email
        values.put(KEY_CREATED_AT, created_at); // Created At
    //    values.put(KEY_TOTAL_USAGE, total_usage); // Total_usage

        // Inserting Row
        db.insert(TABLE_LOGIN, null, values);

        db.close(); // Closing database connection
    }

    /**
     * Storing user details in database
     * */
    public void updateUser(String email, String total_usage) {
        String selectQuery = "UPDATE login SET total_usage = 132 WHERE email = 'sampleMail'";

        SQLiteDatabase db = this.getWritableDatabase();

        db.execSQL(selectQuery);

        db.setTransactionSuccessful();
        db.close(); 
    }

    /**
     * Getting user data from database
     * */
    public HashMap<String, String> getUserDetails(){
        HashMap<String,String> user = new HashMap<String,String>();
        String selectQuery = "SELECT  * FROM " + TABLE_LOGIN;

        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        // Move to first row
        cursor.moveToFirst();
        if(cursor.getCount() > 0){
            user.put("name", cursor.getString(1));
            user.put("email", cursor.getString(2));
            user.put("uid", cursor.getString(3));
            user.put("created_at", cursor.getString(4));
        }
        cursor.close();
        db.close();
        // return user
        return user;
    }

    /**
     * Getting user login status
     * return true if rows are there in table
     * */
    public int getRowCount() {
        String countQuery = "SELECT  * FROM " + TABLE_LOGIN;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        int rowCount = cursor.getCount();
        db.close();
        cursor.close();

        // return row count
        return rowCount;
    }

    /**
     * Re crate database
     * Delete all tables and create them again
     * */
    public void resetTables(){
        SQLiteDatabase db = this.getWritableDatabase();
        // Delete All Rows
        db.delete(TABLE_LOGIN, null, null);
        db.close();
    }

}

我的问题是:为什么表 login 从未创建？难道我做错了什么？解决这样的问题不可能这么难。我在使用 Sqlite 时遇到了很多困难。如果有人能帮助我那就太好了。我使用 phpmyadmin 作为数据库

应用程序本身没有错误，logcat 为空

我删除并运行了该应用程序数十亿次，但它不起作用

也许这个信息很有用:当我在终端中输入 adb 时，它无法被识别。

为什么 onCreate() 方法从未被调用？如果我误用了一些术语，请原谅我，因为我因为 1 周没有解决这个问题而变得疯狂:(

我在代码中使用了这个:http://www.androidhive.info/2012/01/android-login-and-registration-with-php-mysql-and-sqlite/

<小时/>

下面的代码不起作用:

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

Answer 1

除非调用 SQLiteOpenHelper 类的 getWritableDatabase() 或 getReadableDatabase() 方法，否则不会创建数据库。

你可以做的是存储一个变量字段 SQLiteDatabase db; 然后在构造函数中调用db = db.getWriteableDatabase()/readable();

我认为这会解决你的问题:)

编辑:试试这个:

private SQLiteDatabase db;

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

public void open(){
     db = getWritableDatabase();
}

然后做这样的事情:

DatabaseHandler dh = new DatabaseHandler();
dh.open()

如果这仍然不起作用，请尝试 https://www.google.se/?gws_rd=ssl#q=android+sqlite+oncreate+not+called

祝你好运!