Qt实现下载文件并输出进度

可以使用Qt提供的QNetworkAccessManager类来实现文件的下载，并通过QProgressDialog实现进度条的显示。

以下是一个简单的示例代码：

#include <QtWidgets>
#include <QtNetwork>

class Downloader : public QObject {
    Q_OBJECT

public:
    Downloader(QObject *parent = nullptr) : QObject(parent) {}

    void download(const QUrl &url) {
        QNetworkRequest request(url);
        reply = manager.get(request);

        connect(reply, &QNetworkReply::downloadProgress, this, &Downloader::onDownloadProgress);
        connect(reply, &QNetworkReply::finished, this, &Downloader::onDownloadFinished);
    }

signals:
    void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);
    void downloadFinished(QByteArray data);

private slots:
    void onDownloadProgress(qint64 bytesReceived, qint64 bytesTotal) {
        emit downloadProgress(bytesReceived, bytesTotal);
    }

    void onDownloadFinished() {
        QByteArray data = reply->readAll();
        reply->deleteLater();
        emit downloadFinished(data);
    }

private:
    QNetworkAccessManager manager;
    QNetworkReply *reply = nullptr;
};

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {
        urlLineEdit = new QLineEdit();
        downloadButton = new QPushButton("Download");
        progressBar = new QProgressBar();
        statusLabel = new QLabel();

        QVBoxLayout *layout = new QVBoxLayout();
        layout->addWidget(urlLineEdit);
        layout->addWidget(downloadButton);
        layout->addWidget(progressBar);
        layout->addWidget(statusLabel);

        QWidget *centralWidget = new QWidget();
        centralWidget->setLayout(layout);
        setCentralWidget(centralWidget);

        connect(downloadButton, &QPushButton::clicked, this, &MainWindow::onDownloadButtonClicked);
    }

private slots:
    void onDownloadButtonClicked() {
        QUrl url = QUrl::fromUserInput(urlLineEdit->text());
        if (!url.isValid()) {
            QMessageBox::warning(this, "Error", "Invalid URL");
            return;
        }

        downloader.download(url);

        progressDialog = new QProgressDialog(this);
        progressDialog->setLabelText("Downloading...");
        progressDialog->setMinimum(0);
        progressDialog->setMaximum(100);
        progressDialog->setWindowModality(Qt::WindowModal);
        progressDialog->show();

        connect(&downloader, &Downloader::downloadProgress, this, &MainWindow::onDownloadProgress);
        connect(&downloader, &Downloader::downloadFinished, this, &MainWindow::onDownloadFinished);
    }

    void onDownloadProgress(qint64 bytesReceived, qint64 bytesTotal) {
        int progress = bytesReceived * 100 / bytesTotal;
        progressBar->setValue(progress);
        progressDialog->setValue(progress);
    }

    void onDownloadFinished(QByteArray data) {
        statusLabel->setText("Download finished");
        QMessageBox::information(this, "Info", "Download finished");

        progressDialog->close();
        delete progressDialog;

        // TODO: handle downloaded data
    }

private:
    QLineEdit *urlLineEdit;
    QPushButton *downloadButton;
    QProgressBar *progressBar;
    QLabel *statusLabel;

    Downloader downloader;
    QProgressDialog *progressDialog = nullptr;
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    MainWindow mainWindow;
    mainWindow.show();

    return app.exec();
}

#include "main.moc"

在这个例子中，我们创建了一个Downloader类，它使用QNetworkAccessManager来下载文件，并通过信号和槽机制来实现进度条的更新和下载完成的处理。主窗口类MainWindow中，我们使用QLineEdit和QPushButton来获取用户输入的下载链接，并使用QProgressBar和QLabel来显示进度和状态信息。在下载按钮被点击时，我们创建一个QProgressDialog来显示下载进度，并连接Downloader类的信号和槽函数来更新进度条和处理下载完成的事件。