Java 未在Android应用程序中使用SQLite创建表

我尝试在应用程序中使用sqlite创建一个表

这是我的密码：

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();
    }

}

---

在调用SQLiteOpenHelper类的getWritableDatabase（）或getReadableDatabase（）方法之前，不会创建数据库

您可以做的是存储一个变量字段

sqlitedb数据库
然后在构造函数中调用
db=db.getWriteableDatabase（）/readable（）

我想这会解决你的问题：）

编辑：尝试以下操作：

private SQLiteDatabase db;

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

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

然后像这样做：

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

如果这仍然不起作用，试试看

祝你好运
 如果我错了，请纠正我，但我已经在updateUser（）函数中这样做了。您是否尝试在构造函数中调用getWriteable？在新设备上第一次调用getWriteable/readable时，应调用onCreate，如果db版本号更改，则调用onUpgrade。因此，即使您将应用程序从ide重新上传到手机上，onCreate也只会在您第一次上传应用程序时调用一次。请您编写代码（或者我必须将代码放在哪里）？通常情况下，我不会直接要求提供代码，但这个问题浪费了1周的时间，因为我将getWriteableDatabase（）放在构造函数DatabaseHandler中。如果这不能解决问题，请回来；）不起作用。先生，如果您能帮我解决这个问题，我将不胜感激
DatabaseHandler dh = new DatabaseHandler();
dh.open()