参考:QFileDialog 的文档,完成对某个目录下的多个图片文件的选择。然后,结合使 用 QLabel/QImage/QPixmap 来显示图片的示例项目 viewer-demo,实现图片的依次浏览,此时按下 space/ backspace 键,或者用鼠标点击 next/previous 菜单项,可以切换显示下一张/上一张图片;当浏览到最后/第 一张图片时,程序给出相应的提示

好的，下面是一个基于 viewer-demo 的示例程序，实现对目录下多张图片的浏览和切换：

#include <QApplication>
#include <QMainWindow>
#include <QMenuBar>
#include <QFileDialog>
#include <QDirIterator>
#include <QLabel>
#include <QPixmap>
#include <QKeyEvent>

class Viewer : public QMainWindow
{
public:
    Viewer(QWidget *parent = nullptr);
    void showImages(const QStringList &fileNames);

protected:
    void keyPressEvent(QKeyEvent *event) override;

private:
    QLabel *imageLabel;
    QStringList imageFiles;
    int currentIndex;
};

Viewer::Viewer(QWidget *parent)
    : QMainWindow(parent)
{
    imageLabel = new QLabel(this);
    imageLabel->setAlignment(Qt::AlignCenter);
    setCentralWidget(imageLabel);

    QMenuBar *menuBar = new QMenuBar(this);
    setMenuBar(menuBar);

    QMenu *fileMenu = new QMenu(tr("File"), this);
    menuBar->addMenu(fileMenu);

    QAction *openAction = new QAction(tr("Open..."), this);
    fileMenu->addAction(openAction);
    connect(openAction, &QAction::triggered, [=]() {
        QStringList filters;
        filters << "*.png" << "*.jpg" << "*.jpeg" << "*.bmp";
        QString dir = QFileDialog::getExistingDirectory(this, tr("Select Directory"), QDir::homePath());
        if (!dir.isEmpty()) {
            QDirIterator it(dir, filters, QDir::Files, QDirIterator::Subdirectories);
            showImages(QStringList());
            while (it.hasNext()) {
                imageFiles << it.next();
            }
            if (!imageFiles.isEmpty()) {
                currentIndex = 0;
                showImages(QStringList() << imageFiles[currentIndex]);
            }
        }
    });

    QMenu *viewMenu = new QMenu(tr("View"), this);
    menuBar->addMenu(viewMenu);

    QAction *previousAction = new QAction(tr("Previous"), this);
    viewMenu->addAction(previousAction);
    connect(previousAction, &QAction::triggered, [=]() {
        if (currentIndex > 0) {
            currentIndex--;
            showImages(QStringList() << imageFiles[currentIndex]);
        } else {
            QMessageBox::warning(this, tr("Viewer"), tr("This is the first image."));
        }
    });

    QAction *nextAction = new QAction(tr("Next"), this);
    viewMenu->addAction(nextAction);
    connect(nextAction, &QAction::triggered, [=]() {
        if (currentIndex < imageFiles.count() - 1) {
            currentIndex++;
            showImages(QStringList() << imageFiles[currentIndex]);
        } else {
            QMessageBox::warning(this, tr("Viewer"), tr("This is the last image."));
        }
    });
}

void Viewer::showImages(const QStringList &fileNames)
{
    if (fileNames.isEmpty()) {
        imageLabel->setText(tr("No image."));
        return;
    }
    QPixmap pixmap(fileNames.first());
    if (pixmap.isNull()) {
        imageLabel->setText(tr("Invalid image."));
        return;
    }
    imageLabel->setPixmap(pixmap.scaled(imageLabel->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation));
    setWindowTitle(fileNames.first());
}

void Viewer::keyPressEvent(QKeyEvent *event)
{
    switch (event->key()) {
    case Qt::Key_Space:
        emit ui->actionNext->triggered();
        break;
    case Qt::Key_Backspace:
        emit ui->actionPrevious->triggered();
        break;
    default:
        QMainWindow::keyPressEvent(event);
    }
}

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

这个程序与 viewer-demo 相似，但加入了一个 openAction 菜单项，用于打开一个文件夹选择对话框，并显示其中的所有图片。浏览图片时，可以使用 previousAction 和 nextAction 菜单项、空格键和退格键进行切换。当浏览到第一张或最后一张图片时，程序会给出相应的提示。