QT Creator有问题。我正在写一个程序，需要一个数据库。我选择了SQLITE，当我直接在MainWindow的构造函数中打开到数据库的连接时，一切正常。但是当我使用我的类Database或它的方法时，到数据库的连接不再工作，我得到错误
打开QSqlError时出错（“，“未加载驱动程序”，“未加载驱动程序”）.
QtSql在示例、方法或指针方面是否有问题？
我将非常感谢提示，帮助或参考解决方案，因为我已经被困了大约12个小时了。
我的mainwindow.cpp时，它的工作。

#include "HeaderLibary.h"
#include "ui_mainwindow.h"
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    this->setMaximumHeight(MAX_WINDOW_HEIGHT);
    this->setMinimumHeight(MIN_WINDOW_HEIGHT);
    this->setMaximumWidth(MAX_WINDOW_WIDTH);
    this->setMinimumWidth(MIN_WINDOW_WIDTH);

    QFont font;
    font.setPixelSize(FONT_SIZE);
    font.setBold(true);
    font.setFamily(FONT_FAMILY);

    QString buffer;
    QGridLayout *windowLayout = new QGridLayout;

    matrix *inputMatrix = new matrix("input",MAXLENGTH,false,QLINEEDIT_HEIGHT,QLINEEDIT_WIDTH,font,5,5,true,1);
    inputMatrix->set_matrix();
    this->inputWidgets = inputMatrix->getMatrixWidgets();

    buffer = "Hello User, welcome to AES - Advanced Encryption Standard!";
    QLabel *title = inputMatrix->setLabel(buffer,MAX_WINDOW_WIDTH,LABEL_HIGHT);

    font.setPointSize(FONT_SIZE_TEXT);
    buffer = "With AES you can encrypt messages of up to 16 characters or 16 Bytes."
             "\n\nPlease enter your message in this matrix. One character per field in numbered order.";
    QLabel *text = inputMatrix->setLabel(buffer,MAX_WINDOW_WIDTH,LABEL_HIGHT);

    QPushButton *startBtn = inputMatrix->setButton("Start",BTN_WIDTH,BTN_HEIGHT);
    connect(startBtn,SIGNAL(clicked()),this,SLOT(start_clicked()));

    windowLayout->addWidget(title,0,0,1,2,Qt::AlignCenter);
    windowLayout->addWidget(text,1,0,1,2,Qt::AlignCenter);
    windowLayout->addLayout(inputMatrix->getLayout(),2,0,1,2,Qt::AlignCenter);
    windowLayout->addWidget(startBtn,3,1,1,1,Qt::AlignRight);

    QWidget *widget = new QWidget();
    widget->setLayout(windowLayout);
    setCentralWidget(widget);

    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("AES_DB.db");

    if(!db.open())
        qDebug()<< db.lastError();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::start_clicked()
{
    QSqlDatabase db;
    QSqlQuery qry;
    QString tableName = "orginalMsgLetters";

    QString buffer= QString("DROP TABLE %1;").arg(tableName);
    if(!qry.exec(buffer))
        qDebug()<< qry.lastError();

    buffer = QString("CREATE TABLE IF NOT EXISTS %1 (id INTEGER NOT NULL PRIMARY KEY, itemValue VARCHAR(20));").arg(tableName);

    if(!qry.exec(buffer))
        qDebug()<< qry.lastError();

    bool check = false;
    int index = 0;

    while(!check){

        if(inputWidgets->at(index)->text() == ""){
            QMessageBox::information(this,tr("Error"), tr("Please fill out each box to continue"));
            return;
        }
        else if(inputWidgets->at(index)->text() == "ü" || inputWidgets->at(index)->text() == "ä" || inputWidgets->at(index)->text() == "ö" || inputWidgets->at(index)->text() == "ß"){
            QMessageBox::information(this,tr("Error"), tr("Please don't use Ü/ü, Ä/ä, Ö/ö or ß "));
            return;
        }
        else {
            if(index+1 == MAXLENGTH)
                check = true;
            else
                index++;
        }
    }

    for (int i = 0; i < MAXLENGTH; ++i) {

        buffer=QString("INSERT INTO %1 (id,itemValue)VALUES (%2,%3);").arg(tableName).arg(i).arg(this->inputWidgets->at(i)->text());

        if(!qry.exec(buffer))
            qDebug()<<qry.lastError();

        buffer=QString("SELECT * FROM %1 WHERE id=%2").arg(tableName).arg(i);
        if(!qry.exec(buffer))
            qDebug()<<qry.lastError();
        while(qry.next())
            qDebug()<< qry.value(1).toString();
     }

    db.close();
}

我的主窗口. h

#pragma once

#include "HeaderLibary.h"
#include "Config_File.h"


QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

private:
    QList<QLineEdit*>* inputWidgets;
    //Database *db = new Database();

    QSqlDatabase *db = new QSqlDatabase;
    QSqlQuery *qry = new QSqlQuery;

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void start_clicked();

private:
    Ui::MainWindow *ui;
};

我的数据库. cpp
当我在我的mainwindow.cpp中使用这个的任何方法来初始化数据库时，它不会工作，我得到错误.“驱动程序未加载”

#include "database.h"

Database::Database(){

}

Database::~Database(){
}

void Database::deleteTable(QString tableName){
    QSqlQuery qry;
    QString buffer = QString("DROP TABLE %1;").arg(tableName);
    qry.prepare(buffer);
    qry.exec();

}

void Database::connect(){
    QSqlDatabase db;
    db.addDatabase("QSQLITE");
    db.setDatabaseName("AES_DB.db");
    if(!db.open())
        qDebug()<< "Error open "<< db.lastError();
}

void Database::addValueToTable(QString tableName,int id, QString value){
    QSqlQuery qry;
    QString buffer = QString("INSERT INTO %1 (id,itemValue)VALUES (%2,%3);").arg(tableName).arg(id).arg(value);
    qry.prepare(buffer);
    if(!qry.exec()){
        qDebug()<< qry.lastError();
        qDebug()<< "\n insert Error \n";
    }

}

void Database::createTable(QString tableName){

    QSqlQuery qry;
    QString buffer = QString("CREATE TABLE IF NOT EXISTS %1 (id INTEGER NOT NULL PRIMARY KEY, itemValue VARCHAR(20));").arg(tableName);

    if(!qry.exec(buffer)){
        qDebug()<< qry.lastError();
        qDebug()<< "\n create Error \n";
    }

}

void Database::close(){

    QSqlDatabase db;
    db.close();

}

QString Database::getValueFromTable(QString tableName,int id){

    QSqlQuery qry;
    QString string = QString("SELECT * FROM %1 WHERE id=%2").arg(tableName).arg(id);
    qry.prepare(string);
    if(!qry.exec(string)){
        qDebug()<< qry.lastError();
        qDebug()<< "\n get Error \n";
    }
    while(qry.next())
        return qry.value(1).toString();

}

我的数据库. h

#pragma once

#include "Config_File.h"
#include "HeaderLibary.h"

class Database
{

private:

public:
    Database();
    ~Database();
    void connect();
    void addValueToTable(QString tableName,int id, QString value);
    void deleteTable (QString tableName);
    void createTable(QString tableName);
    QString getValueFromTable(QString tableName,int id);
    void close();
};
'''

  [1]: https://i.stack.imgur.com/48zP0.png