1代码：

1.1演示图：

加上这个passwordline->setEchoMode(QLineEdit::Password);

1.2cpp文件：

#include "widget.h"
 
 
Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
 
    this->resize(300,200);
    this->setWindowTitle("登录窗口");
 
    usrname=new QLabel("用户名",this);
    password=new QLabel("密码",this);
 
    usrnameline=new QLineEdit(this);
    passwordline=new QLineEdit(this);
    passwordline->setEchoMode(QLineEdit::Password);
 
    regist_btn=new QPushButton("注册",this);
    login_btn=new QPushButton("登录",this);
 
    QGridLayout* up_late=new QGridLayout;
    up_late->addWidget(usrname,0,0);
    up_late->addWidget(usrnameline,0,1);
    up_late->addWidget(password,1,0);
    up_late->addWidget(passwordline,1,1);
 
 
    QHBoxLayout* shui_ping=new QHBoxLayout;
    shui_ping->addWidget(regist_btn);
    shui_ping->addWidget(login_btn);
 
    QVBoxLayout* together=new QVBoxLayout(this);
    together->addLayout(up_late);
    together->addLayout(shui_ping);
 
    connect(passwordline,&QLineEdit::textChanged,[](const QString& text){
        QRegExp exp("^[A-Z]+[a-z0-9_]{7,}");
 
        if(exp.exactMatch(text)){
           qDebug()<<"输入格式正确";
        }else{
           qDebug()<<"输入格式错误";
        }
    });
 
    connect(login_btn,&QPushButton::clicked,[=](){
        if(usrnameline->text()=="peter"&&passwordline->text()=="A1234567"){
            QMessageBox::information(this,"提示","输入正确");
 
        }else{
            QMessageBox::information(this,"提示","输入错误");
        }
    });
}
 
Widget::~Widget()
{
}