需要帮助在QT中将QString值从一个屏幕传递到另一个屏幕吗 P.>我对QT是全新的，并且只对C++有一些基本的理解，但是我很难把用户名qStand变量从MixWOWO.CPP传递到CuutoLogin .CPP。我试着通过构造函数传递它，但这似乎不起作用，我正在努力理解插槽是如何工作的

main window.cpp

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    if (!connOpen())
        ui->Status->setText("Failed to open the database");
    else
        ui->Status->setText("Database Conneceted...");
}


MainWindow::~MainWindow()
{
    delete ui;
}
void MainWindow::buttonLogin()
{
    QString username = ui->lineUser->text();
    QString password = ui->linePassword->text();

    if (!connOpen())
    {
        qDebug() << "Failed To Open the Database";
    }

    connOpen();
    QSqlQuery qry;
    qry.prepare("select * from owner where userid='"+username +"' and password='"+password +"' and rank='3'");

    if (qry.exec())
    {
        int count = 0;
        while (qry.next())
        {
            count++;
        }
        if(count ==1)
        {
            QMessageBox::information(this, "Login", "Username and password is correct");
            hide();
            connClose();
            customerLogin *userLogin = new customerLogin();
            userLogin->show();
        }
        else if (count != 1)
        {
            if(qry.exec("select * from owner where userid='"+username +"' and password='"+password +"' and rank='1'"))
            {
            int count = 0;
            while (qry.next())
            {
                count++;
            }
            if(count ==1)
            {
                QMessageBox::information(this, "Login", "Username and password is correct");
                hide();
                connClose();
                secAdminLogin *adminLogin = new secAdminLogin;
                adminLogin -> show();
            }
                else
                {
                    QMessageBox::warning(this,"Login", "Username and password is not correct!");
                }
            }
        }
    }
}

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


}


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

void customerLogin::setUsername(QString username)
{
    m_username = username;
}

---

创建customerLogin后，可以添加一个函数从MainWindow.cpp传递用户名，如下所示

customerLogin *userLogin = new customerLogin();
userLogin->setUsername(username);
userLogin->show();

您需要将此函数添加到customerLogin的.h和.cpp中

customerLogin.h

private:
QString m_username;

public:
void setUsername(QString username);

customerLogin.cpp

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    if (!connOpen())
        ui->Status->setText("Failed to open the database");
    else
        ui->Status->setText("Database Conneceted...");
}


MainWindow::~MainWindow()
{
    delete ui;
}
void MainWindow::buttonLogin()
{
    QString username = ui->lineUser->text();
    QString password = ui->linePassword->text();

    if (!connOpen())
    {
        qDebug() << "Failed To Open the Database";
    }

    connOpen();
    QSqlQuery qry;
    qry.prepare("select * from owner where userid='"+username +"' and password='"+password +"' and rank='3'");

    if (qry.exec())
    {
        int count = 0;
        while (qry.next())
        {
            count++;
        }
        if(count ==1)
        {
            QMessageBox::information(this, "Login", "Username and password is correct");
            hide();
            connClose();
            customerLogin *userLogin = new customerLogin();
            userLogin->show();
        }
        else if (count != 1)
        {
            if(qry.exec("select * from owner where userid='"+username +"' and password='"+password +"' and rank='1'"))
            {
            int count = 0;
            while (qry.next())
            {
                count++;
            }
            if(count ==1)
            {
                QMessageBox::information(this, "Login", "Username and password is correct");
                hide();
                connClose();
                secAdminLogin *adminLogin = new secAdminLogin;
                adminLogin -> show();
            }
                else
                {
                    QMessageBox::warning(this,"Login", "Username and password is not correct!");
                }
            }
        }
    }
}

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


}


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

void customerLogin::setUsername(QString username)
{
    m_username = username;
}

另外，您正在使用调用connOpen（）两次

if (!connOpen())
{
    qDebug() << "Failed To Open the Database";
}
connOpen();

if（！connOpen（））
{
qDebug（）除了bio建议的方法外，您还可以在MainWindow.cpp中声明一个全局变量，并在customerLogin.cpp中将其声明为“extern”，以使其可访问

用于通过信号/插槽进行“用户名”通信


在MainWindow.h中声明一个带有一个QString参数的信号
在customerLogin.h中声明具有一个QString参数的插槽
创建customerLogin对象后，连接信号和插槽
在需要时（在本例中，在userLogin->show（）之前）以“username”变量作为参数发出信号