槽函数声明

private slots:
    void on_ed_textChanged();
    void on_pushButton_clicked();
};

槽函数定义

void Widget::on_ed_textChanged()//文本框
{
    if(ui->ed1->text().length()>=5
            &&ui->ed2->text().length()>=5)
    {
        ui->pushButton->setStyleSheet("background-color:green");
    }
    else
        ui->pushButton->setStyleSheet("background-color:red");
}

void Widget::on_pushButton_clicked()//按钮
{
    if(ui->ed1->text()=="Admin"
            &&ui->ed2->text()=="12345")
        qDebug("登录成功");
    else
    {
        qDebug("账号或密码错误，请重新输入");
        ui->ed1->clear();
        ui->ed2->clear();
    }
}

信号与槽连接

    QObject::connect(ui->ed1,&QLineEdit::textChanged,
                     this,&Widget::on_ed_textChanged);
    QObject::connect(ui->ed2,&QLineEdit::textChanged,
                     this,&Widget::on_ed_textChanged);

    QObject::connect(ui->pushButton,&QPushButton::clicked,
                     this,&Widget::on_pushButton_clicked);