CODEWITHSUNDEEP
c++qtsignals-slots
reckless
reckless

Reputation: 933

Pass a pointer using Qt signals and slots

So I have the following function:

void parseData()
{
    // DownloadManager and Post subclass QObject
    DownloadManager* downloadManager = new DownloadManager();
    Post* post = new Post(mPostsModel);

    // using qt signal and slots I would like to retrieve the Post in the onFileDownloaded slot
    connect(downloadManager, &DownloadManager::allDownloadsFinished, this, &MediaFetcher::onFileDownloaded);

}

Now I would like to get to my Post* post in my MediaFetcher::onFileDownloaded slot, something like this:

void MediaFetcher::onFileDownloaded()
{
    qDebug() << "files downloaded";
    DownloadManager* downloadManager = qobject_cast<DownloadManager*>(sender());
    Post* post = getPost(); // how do I get this???
    mPostsModel->append(post);

    downloadManager->deleteLater();
}

One solution that I think is very ugly (also I think it causes a memory leak) was to use QObject::setProperty and then add my Post* to the downloadManager and then get that in the slot (I had use qvariant_cast). In parseData()

    QVariant postVariant = QVariant::fromValue(post);
    downloadManager->setProperty("post", postVariant);

Then in onFilesDownloaded():

    Post* post = qvariant_cast<Post*>(downloadManager->property("post"));

Does anyone know how can this be done in a more elegant way?

Upvotes: 0

Views: 2384

Answers (1)

apalomer
apalomer

Reputation: 1935

The way I would do this requires either to change the signature of your allDownloadsFinished signal to pass a Post: 

class downloadManager : public QWidget
{
// Normal constructors and destructor and macros

signals:
   void allDownloadsFinished(Post* post);

};

or to add a new signal to downloadManager to be able to send Post*. In any case, you'll have to register the Post meta-type:

qRegisterMetaType<Post*>("Post*");

Obviously, this requires your slot to accept the Post* type.

Upvotes: 2

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