封装qt http文件下载类

#include <QApplication>

#include <QtWidgets>

#include <QtNetwork>

//downloads one file at a time, using a supplied QNetworkAccessManager object

class FileDownloader : public QObject{

    Q_OBJECT

public:

    explicit FileDownloader(QObject* parent= nullptr)

        :QObject(parent)

    {

        nam = new QNetworkAccessManager(this);

    }

    ~FileDownloader(){

        //destructor cancels the ongoing dowload (if any)

        if(networkReply){

            a_abortDownload();

        }

    }

    //call this function to start downloading a file from url to fileName

    void startDownload(QUrl url, QString fileName){

        if(networkReply) return;

        destinationFile.setFileName(fileName);

        if(!destinationFile.open(QIODevice::WriteOnly)) return;

        emit goingBusy();

        QNetworkRequest request(url);

        networkReply= nam->get(request);

        connect(networkReply, &QIODevice::readyRead, this, &FileDownloader::readData);

        connect(networkReply, &QNetworkReply::downloadProgress,

                this, &FileDownloader::downloadProgress);

        connect(networkReply, &QNetworkReply::finished,

                this, &FileDownloader::finishDownload);

    }

    //call this function to abort the ongoing download (if any)

    void abortDownload(){

        if(!networkReply) return;

        a_abortDownload();

        emit backReady();

    }

    //connect to the following signals to get information about the ongoing download

    Q_SIGNAL void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);

    Q_SIGNAL void downloadSuccessful();

    Q_SIGNAL void downloadError(QString errorString);

    //the next two signals are used to indicate transitions between busy and

    //ready states of the file downloader, they can be used to update the GUI

    Q_SIGNAL void goingBusy();

    Q_SIGNAL void backReady();

private:

    Q_SLOT void readData(){

        QByteArray data= networkReply->readAll();

        destinationFile.write(data);

    }

    Q_SLOT void finishDownload(){

        if(networkReply->error() != QNetworkReply::NoError){

            //failed download

            a_abortDownload();

            qDebug() << "networkReply->errorString()"<<networkReply->errorString();

            emit downloadError(networkReply->errorString());

        } else {

            //successful download

            destinationFile.close();

            networkReply->deleteLater();

            qDebug() << "downloadSuccessful";

            emit downloadSuccessful();

        }

        emit backReady();

    }

    //private function, cleans things up when the download is aborted

    //(due to an error or user interaction)

    void a_abortDownload(){

        networkReply->abort();

        networkReply->deleteLater();

        destinationFile.close();

        destinationFile.remove();

    }

    QNetworkAccessManager* nam;

    QUrl downloadUrl;

    QFile destinationFile;

    QPointer<QNetworkReply> networkReply;

};

//A sample GUI application that uses the above class

class Widget : public QWidget{

    Q_OBJECT

public:

    explicit Widget(QWidget* parent= nullptr):QWidget(parent){

        layout.addWidget(&lineEditUrl, 0, 0);

        layout.addWidget(&buttonDownload, 0, 1);

        layout.addWidget(&progressBar, 1, 0);

        layout.addWidget(&buttonAbort, 1, 1);

        layout.addWidget(&labelStatus, 2, 0, 1, 2);

        lineEditUrl.setPlaceholderText("URL to download");

        connect(&fileDownloader, &FileDownloader::downloadSuccessful,

                this, &Widget::downloadFinished);

        connect(&fileDownloader, &FileDownloader::downloadError,

                this, &Widget::error);

        connect(&fileDownloader, &FileDownloader::downloadProgress,

                this, &Widget::updateProgress);

        connect(&buttonDownload, &QPushButton::clicked,

                this, &Widget::startDownload);

        connect(&buttonAbort, &QPushButton::clicked,

                this, &Widget::abortDownload);

        showReady();

        //use goingBusy() and backReady() from FileDownloader signals to update the GUI

        connect(&fileDownloader, &FileDownloader::goingBusy, this, &Widget::showBusy);

        connect(&fileDownloader, &FileDownloader::backReady, this, &Widget::showReady);

    }

    ~Widget() = default;

    Q_SLOT void startDownload(){

        if(lineEditUrl.text().isEmpty()){

            QMessageBox::critical(this, "Error", "Enter file Url", QMessageBox::Ok);

            return;

        }

        QString fileName =

                QFileDialog::getSaveFileName(this, "Destination File");

        if(fileName.isEmpty()) return;

        QUrl url= lineEditUrl.text();

        fileDownloader.startDownload(url, fileName);

    }

    Q_SLOT void abortDownload(){

        fileDownloader.abortDownload();

    }

    Q_SLOT void downloadFinished(){

        labelStatus.setText("Download finished successfully");

    }

    Q_SLOT void error(QString errorString){

        labelStatus.setText(errorString);

    }

    Q_SLOT void updateProgress(qint64 bytesReceived, qint64 bytesTotal){

        progressBar.setRange(0, bytesTotal);

        progressBar.setValue(bytesReceived);

    }

private:

    Q_SLOT void showBusy(){

        buttonDownload.setEnabled(false);

        lineEditUrl.setEnabled(false);

        buttonAbort.setEnabled(true);

        labelStatus.setText("Downloading. . .");

    }

    Q_SLOT void showReady(){

        buttonDownload.setEnabled(true);

        lineEditUrl.setEnabled(true);

        buttonAbort.setEnabled(false);

        progressBar.setRange(0,1);

        progressBar.setValue(0);

    }

    QGridLayout layout{this};

    QLineEdit lineEditUrl;

    QPushButton buttonDownload{"Start Download"};

    QProgressBar progressBar;

    QPushButton buttonAbort{"Abort Download"};

    QLabel labelStatus{"Idle"};

//    QNetworkAccessManager nam;

//    FileDownloader fileDownloader{&nam};

    FileDownloader fileDownloader;

};

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

    QApplication a(argc, argv);

    Widget w;

    w.show();

    return a.exec();

}

#include "main.moc"