用QT写一个查看图片的程序，要求点击“上一张”和“下一张”实现显示图片，基类为qdialog

以下是一个简单的实现：

#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QDir>
#include <QDebug>

class ImageViewer : public QDialog
{
    Q_OBJECT

public:
    ImageViewer(QWidget *parent = nullptr);

private slots:
    void onPreviousClicked();
    void onNextClicked();

private:
    QLabel *m_imageLabel;
    QPushButton *m_previousButton;
    QPushButton *m_nextButton;
    QStringList m_imageList;
    int m_currentIndex;
};

ImageViewer::ImageViewer(QWidget *parent)
    : QDialog(parent)
{
    m_imageLabel = new QLabel(this);
    m_previousButton = new QPushButton(tr("上一张"), this);
    m_nextButton = new QPushButton(tr("下一张"), this);

    QHBoxLayout *buttonLayout = new QHBoxLayout;
    buttonLayout->addWidget(m_previousButton);
    buttonLayout->addWidget(m_nextButton);

    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addWidget(m_imageLabel);
    mainLayout->addLayout(buttonLayout);

    setLayout(mainLayout);

    // 查找图片文件
    QDir imagesDir(QCoreApplication::applicationDirPath() + "/images");
    QStringList filters;
    filters << "*.jpg" << "*.jpeg" << "*.png" << "*.bmp";
    m_imageList = imagesDir.entryList(filters, QDir::Files | QDir::NoSymLinks);
    m_currentIndex = 0;
    if (m_imageList.size() > 0) {
        QString imagePath = imagesDir.absoluteFilePath(m_imageList.at(m_currentIndex));
        m_imageLabel->setPixmap(QPixmap(imagePath));
        m_imageLabel->setScaledContents(true);
    }

    connect(m_previousButton, &QPushButton::clicked, this, &ImageViewer::onPreviousClicked);
    connect(m_nextButton, &QPushButton::clicked, this, &ImageViewer::onNextClicked);
}

void ImageViewer::onPreviousClicked()
{
    if (m_imageList.size() > 0) {
        m_currentIndex--;
        if (m_currentIndex < 0) {
            m_currentIndex = m_imageList.size() - 1;
        }
        QString imagePath = QDir::currentPath() + "/images/" + m_imageList.at(m_currentIndex);
        m_imageLabel->setPixmap(QPixmap(imagePath));
    }
}

void ImageViewer::onNextClicked()
{
    if (m_imageList.size() > 0) {
        m_currentIndex++;
        if (m_currentIndex >= m_imageList.size()) {
            m_currentIndex = 0;
        }
        QString imagePath = QDir::currentPath() + "/images/" + m_imageList.at(m_currentIndex);
        m_imageLabel->setPixmap(QPixmap(imagePath));
    }
}

在构造函数中，我们首先查找指定目录下所有符合条件的图片文件，然后将第一张图片显示在标签上。之后，我们连接“上一张”和“下一张”按钮的点击事件到对应的槽函数。在槽函数中，我们更新当前图片的索引值，然后根据索引值找到对应的图片文件，并将其显示在标签上。需要注意的是，当索引值越界时，我们需要将其重置到合法范围内。