1、先创建一个QT应用程序，在ui中添加一个QFrame控件，后期将这个控件提升为下面自己实现验证码的类就可以显示出来了。

示例代码如下：

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "verification.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();
    
private:
    Ui::MainWindow *ui;

    Verification *verification;
};
#endif // MAINWINDOW_H

mainwindow.cpp

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


MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    verification = ui->frame;  //提升类控件名
}

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

void MainWindow::on_pushButton_clicked()    //点击跟新验证码
{
     verification->Timer_Timeout();
}

主函数：

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

mainwindow.ui

2、右击新添加一个Qt设计师类，在里面实现验证码的随机生成。

代码如下：

verification.h

#ifndef VERIFICATION_H
#define VERIFICATION_H

#include <QPainter>
#include <QTimer>
#include <QFrame>
#include <QChar>
#include <QColor>

class Verification : public QFrame
{
    Q_OBJECT
public:
    Verification(QWidget *parent = Q_NULLPTR);
    ~Verification();

public:
    QString getVerificationCodes() const;   返回一个字符串(默认全为小写)(验证码)
    QChar produceRandomLetters() const;     //随机产生一个字符
    void produceVerificationCodes() const;  //这是一个用来生成验证码的函数
    void produceRandomColors() const;       //产生随机的颜色
    void paintEvent(QPaintEvent *event);    //重写绘制事件,以此来生成验证码
    Qt::GlobalColor* getColor();            //返回设置验证码的颜色
    void Timer_Timeout();
    QString getCaptcha();

private:
    const int letter_number = 4;    //产生字符的数量
    Qt::GlobalColor* m_color;
    QString m_captcha;
    QTimer m_timer;

    enum {                          //枚举分类，也可自己定义
           NUMBER_FLAG,
           UPLETTER_FLAG,
           LOWLETTER_FLAG
       };
    QChar *verificationCode;
    QColor *colorArray;
};

#endif // VERIFICATION_H

verification.cpp

#include "verification.h"
#include <QTime>
#include <QPaintEvent>

Verification::Verification(QWidget *parent)
    :QFrame(parent)
{
    //生成随机种子
    qsrand(QTime::currentTime().second() * 1000 + QTime::currentTime().msec());

//    m_captcha = getVerificationCode();
//    m_color = getColor();
    //    m_timer.start(200);

    colorArray = new QColor[letter_number];
    verificationCode = new QChar[letter_number];
    m_captcha = getVerificationCodes();
}

Verification::~Verification()
{

}

ification::getVerificationCodes() const
{


    QString s ="";
    QChar cTemp;
    for (int i = 0; i < letter_number; ++i)
    {
        cTemp = verificationCode[i];
        s += cTemp>97?cTemp.toUpper():cTemp;
    }
    return s;
}

QChar Verification::produceRandomLetters() const
{
    QChar c;
    int flag = qrand() % letter_number;
    switch (flag)
    {
    case NUMBER_FLAG:c='0' + qrand() % 10; break;
    case UPLETTER_FLAG:c='A' + qrand() % 26; break;
    case LOWLETTER_FLAG:c='a' + qrand() % 26; break;
    default:c=qrand() % 2 ? 'W' : 'D';
    }
    return c;
}

void Verification::produceVerificationCodes() const
{
    for (int i = 0; i < letter_number; ++i)
         verificationCode[i] = produceRandomLetters();
}

void Verification::produceRandomColors() const
{
    for (int i = 0; i < letter_number; ++i)
        colorArray[i] = QColor(qrand() % 255, qrand() % 255, qrand() % 255);
}


void Verification::Timer_Timeout()
{
//    m_captcha = getVerificationCode();
    m_captcha = getVerificationCodes();
//    this->repaint();
    this->update();
}

QString Verification::getCaptcha()
{
    return getVerificationCodes();
}

void Verification::paintEvent(QPaintEvent *event)
{
    painter(this);
    QPoint p;
    //背景设为白色
    painter.fillRect(this->rect(), Qt::white);
    //产生4个不同的字符
    produceVerificationCodes();
    //产生4个不同的颜色
    produceRandomColors();
    //绘制验证码
    for (int i = 0; i < letter_number; ++i)
    {
        p.setX(i*(this->width() / letter_number)+this->width()/14);
        p.setY(this->height() / 1.5);
        painter.setPen(colorArray[i]);
        painter.drawText(p, QString(verificationCode[i]));
    }
    return;
}

3、在主函数里面添加如下代码：

**.h

 Verification *verification;

**.cpp

void VLoginDlg::on_btnClick_clicked()    //点击更新验证码
{
    verification->Timer_Timeout();
}

运行效果图

当点击最右端按钮时，验证码会自动刷新

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