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Thread: Proper file downloading?

  1. #1
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    Question Proper file downloading?

    Currently in a project I'm working on I'm using a slightly modified version of this (emits fileSaved() and takes a save path) to download files like so:

    Qt Code:
    1. QEventLoop imageLoop;
    2. QDownloader *downloader = new QDownloader();
    3. connect(downloader, SIGNAL(fileSaved()), &imageLoop, SLOT(quit()));
    4.  
    5. for(int i = 0; i < imageURLs.length(); i++) {
    6. progressDialog->setValue((int)(100 * (double)i / imageURLs.length()));
    7. progressDialog->setLabelText("Downloading image: " + QString::number(i + 1) + "/" + QString::number(imageURLs.length()));
    8.  
    9. if(progressDialog->wasCanceled())
    10. break;
    11.  
    12. downloader->setFile(imageURLs.at(i), QDir::homePath() + "/images/" + imageNames.at(i) + ".jpg");
    13. imageLoop.exec();
    14. }
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    The program crashes sometimes doing this and I was wondering what I am doing wrong or what is a more common or appropriate way to accomplish this.

    Thanks

  2. #2
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    Default Re: Proper file downloading?

    Run your program in your debugger and when it crashes inspect the stack back trace to determine where, and usually why, it has crashed.

  3. #3
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    Default Re: Proper file downloading?

    Quote Originally Posted by ChrisW67 View Post
    Run your program in your debugger and when it crashes inspect the stack back trace to determine where, and usually why, it has crashed.
    It looks like it's crashing on

    Qt Code:
    1. void QDownloader::onReadyRead()
    2. {
    3. file->write(reply->readAll());
    4. }
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    So I added a quick check to isWritable() and it still end up crashing but file->isOpen() returns false.

    Eventually I determined that the issue was that the finished() signal kept firing before the final readyRead() so the file would close.

    I also ended up moving the

    Qt Code:
    1. connect(manager,SIGNAL(finished(QNetworkReply*)),this,SLOT(onFinished(QNetworkReply*)));
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    statement to the constructor because it was calling the slot an extra time for each file downloaded.

  4. #4
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    Default Re: Proper file downloading?

    Looking at that code you should not need that connect() from the manager at all. You either connect to the QNetworkAccessManager::finished() signal or the QNetworkReply::finished() signal but not both. It's unlikely the reply's finished signal would come before the reply's last readyRead so I would use those.

  5. The following user says thank you to ChrisW67 for this useful post:

    matt4682 (2nd May 2014)

  6. #5
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    Default Re: Proper file downloading?

    Thanks a bunch, it's running flawlessly!

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