.cpp文件 

#include "widget.h"
#include "ui_widget.h"

#include<QDebug>
Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    //更改窗口标题
    setWindowTitle("我爱xyy");

    //更改图标
    setWindowIcon(QIcon(":/icon/icon.png"));

    //设置提示字
    ui->lineEditName->setPlaceholderText("请输入名字");
    ui->lineEditPasswd->setPlaceholderText("请输入密码");
    //密码隐藏
    ui->lineEditPasswd->setEchoMode(QLineEdit::Password);

    /*单行文本框 信号演示*/
    connect(ui->lineEditPasswd,SIGNAL(editingFinished()),this,SLOT(lineEditPasswdEditingFinishSlotFun()));
    connect(ui->lineEditName,SIGNAL(textChanged(QString)),this,SLOT(lineEditUsrnameTextChangedSlotFun(QString)));
    connect(ui->pushButton, SIGNAL( clicked()) ,this, SLOT(login() ) );
    //按键
    ui->radioButton2->setText("登录");        //setText(QString str) 设置显示文本
    ui->radioButton2->setChecked(true);        //setChecked(bool) 设置选中状态
  //按键信号
    connect(ui->radioButton2,SIGNAL(clicked()),this,SLOT(radioButtonChangeFun()));
    connect(ui->radioButton1,SIGNAL(clicked()),this,SLOT(radioButtonChangeFun()));


}
void Widget::login()
{
    //从界面输入
    QString userName = ui->lineEditName->text();
    QString pwd = ui->lineEditPasswd->text();
    if(userName == "woaixyy" && pwd == "123456")
    {
        qDebug()<<"登录成功";
        qDebug()<<"账号 "<<ui->lineEditName->text();
        qDebug()<<"密码 "<<ui->lineEditPasswd->text();
        this->close();
    }
    else
    {
        qDebug()<<"登录失败";
        qDebug()<<"账号 "<<ui->lineEditName->text();
        qDebug()<<"密码 "<<ui->lineEditPasswd->text();

        ui->lineEditPasswd->clear();

    }
}

void Widget::lineEditPasswdEditingFinishSlotFun()//表示文本确认
{
    qDebug()<<__func__;
    qDebug()<<"账号 "<<ui->lineEditName->text();
    qDebug()<<"密码 "<<ui->lineEditPasswd->text();
}

void Widget::lineEditUsrnameTextChangedSlotFun(QString txt) // 密码的内容
{
    /*获取用户刚刚输入的 字符 QChar
           char:   8bit  asccii   256符号
           QChar：16bit  万国码     65536      ，在QT中，所有的字符都是QChar
                               ‘A’ =16bit;
       */

    //获取最后一个字符
       QChar qch = txt[  txt.length()  - 1   ];
       if( (qch > 'z') || ( qch < 'A' )) {
           qDebug()<<"you input is wrong ,invaoid char "<<qch;
           ui->lineEditName->setText("");

       }
       qDebug()<<__func__<<" last char="<<qch;
}
void Widget::radioButtonChangeFun()
{
    qDebug()<<"你选择：";
    if(ui->radioButton2->isChecked())
    {
        qDebug()<<"登录";
    }
    if(ui->radioButton1->isChecked())
    {
        qDebug()<<"注册";
    }
}
Widget::~Widget()
{
    delete ui;
}

.h文件

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
public slots:
    void login();
    void lineEditPasswdEditingFinishSlotFun();
    void lineEditUsrnameTextChangedSlotFun(QString);
    void radioButtonChangeFun();
private:
    Ui::Widget *ui;
};
#endif // WIDGET_H

.ui

现象