I got the answer.
QDir directory = QFileDialog::getExistingDirectory(this, tr("Open Directory"),"/home",
QFileDialog::ShowDirsOnly| QFileDialog::DontResolveSymlinks);
auto listWidget_images = new QListWidget();//set listwidget to display images
listWidget_images->setMinimumSize(1200,400);
listWidget_images->setViewMode(QListWidget::IconMode);
listWidget_images->setIconSize(QSize(320,240));
listWidget_images->setResizeMode(QListWidget::Adjust);
for(const QFileInfo & finfo: directory.entryInfoList()){
ui->listWidget_dirs->addItem(finfo.absoluteFilePath());
}
connect(ui->listWidget_dirs, & QListWidget::itemClicked,[listWidget_images,this](QListWidgetItem *item)
{
listWidget_images->show();
listWidget_images->clear();
QDir directory(item->text());
directory.setNameFilters({"*.png", "*.jpg"});
for(const QFileInfo & finfo: directory.entryInfoList()){
QListWidgetItem *item = new QListWidgetItem(QIcon(finfo.absoluteFilePath()), finfo.fileName());
listWidget_images->addItem(item);
}
});