實現程式碼：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDragEnterEvent>
#include <QDropEvent>
#include <QUrl>
#include <QList>
#include <QMimeData>
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    ui->label->installEventFilter(this);
    ui->label->setAcceptDrops(true);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
 
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if (watched == ui->label) {
            if (event->type() == QEvent::DragEnter) {
                // [[2]]: 當拖放時滑鼠進入label時, label接受拖放的動作
                QDragEnterEvent *dee = dynamic_cast<QDragEnterEvent *>(event);
                dee->acceptProposedAction();
                return true;
            } else if (event->type() == QEvent::Drop) {
                // [[3]]: 當放操作發生後, 取得拖放的資料
                QDropEvent *de = dynamic_cast<QDropEvent *>(event);
                QList<QUrl> urls = de->mimeData()->urls();
 
                if (urls.isEmpty()) { return true; }
                QString path = urls.first().toLocalFile();
 
                // [[4]]: 在label上顯示拖放的圖片
                QImage image(path); // QImage對I/O優化過, QPixmap對顯示優化
                if (!image.isNull()) {
                    image = image.scaled(ui->label->size(),
                                         Qt::KeepAspectRatio,
                                         Qt::SmoothTransformation);
                    ui->label->setPixmap(QPixmap::fromImage(image));
                }
 
                return true;
            }
        }
 
        return QMainWindow::eventFilter(watched, event);
}
 

執行效果：