Constantly generating QPixmap* fails after a number of iterations - qt

I am using the following code in order to generate QPixmap* pointers and then insert them into QHash<QString, QPixmap*> (I will show only the pointers generation code since this is the one that fails).
QPixmap* MyClass::loadImg(QString fileName)
{
QImage qimage(fileName);
if (qimage.isNull()) {
qDebug() << "Cannot load image " << fileName;
}
QPixmap *image = new QPixmap(fileName);
return image;
}
The problem that I have is the following:
For the first about 200 calls the method works fine - it is being called on a loop that iterates through the image files of a directory. Then suddenly the QPixmap* starts returning QPixmap(null) for no apparent reason.QImage is also null when that happens.
I have checked and made sure that the path is fine. Also, I have tried with various sets of images and the same always happens - it runs with no problems the ~200 calls and then starts generating nulls.
Any help would be appreciated.
Thank you.

Just don't create it on heap. QPixmap is implicitly shared.

Related

Qt. Problem with the QFileDialog: setDirectory() and directory()

I have a problem with the QFileDialog class, namely with the setDirectory() and directory() methods. I need to make it so that after opening a file, my program remembers the directory in which the selected file is stored, and the next time QFileDialog is called, it automatically opens the directory that was used last. Here is a snippet of my code:
static QString _st_doc_last_directory;
void MainWindow::open()
{
if (!fileDialog)
{ fileDialog = new QFileDialog(this);
}
if (!_st_doc_last_directory.isEmpty()) fileDialog->setDirectory(_st_doc_last_directory);
QString fileName = fileDialog->getOpenFileName(this, tr("Open Document"), ".", tr("Compressed CAD Models (*.data)"));
if (!fileName.isEmpty())
{ _st_doc_last_directory = fileDialog->directory().dirName();
}
}
The crux of my problem is that when the setDirectory() or directory() method is called, my program crashes with a
"Segmentation fault"
message. How can I fix it, please advise. Thanks in advance.
Whenever you start this method, you have this as the start window: ".". (admittedly I don't know what's going on internally, but I think this leads to this problem).
You can query beforehand whether your defined string is empty. if so you set a path, otherwise you store one in your string. If you don't want to do this from the beginning every time you start the program, you can also use QSettings. This saves you the path in the registry (ie if you use windows).
With QFileInfo you can easily get the path
void MainWindow::open()
{
if(_st_doc_last_directory.isEmpty())
_st_doc_last_directory = QDir::homePath();
QString fileName = QFileDialog::getOpenFileName(this, tr("Open Document"), _st_doc_last_directory, tr("Compressed CAD Models (*.data)"));
QFileInfo info(fileName);
if(!fileName.isEmpty())
_st_doc_last_directory = info.absolutePath();
}

Getting Pixmap is a null pixmap on calling a function 500 times

I am showing a image in qt label. Below is my code:
void MyClass::onPushButtonClicked(QString myurl)
{
this->setCursor(Qt::WaitCursor);
ui.qtImageLabel->clear();
qDebug()<<QTime::currentTime()<<"MyClass: onPushButtonClicked";
QNetworkAccessManager *qnam_push_button_clicked_show_image;
QNetworkReply *reply;
QNetworkRequest request;
request.setHeader( QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded" );
QUrl url(myurl);
request.setUrl(url);
qnam_push_button_clicked_show_image = new QNetworkAccessManager(this);
if(qnam_push_button_clicked_show_image)
{
QObject::connect(qnam_push_button_clicked_show_image, SIGNAL(finished(QNetworkReply*)),
this, SLOT(onPushButtonClickedRequestCompleted(QNetworkReply*)));
reply = qnam_push_button_clicked_show_image->post(request, url.encodedQuery());
QEventLoop loop;
QObject::connect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
loop.exec();
}
}
void MyClass::onPushButtonClickedRequestCompleted(QNetworkReply *reply)
{
qDebug()<<QTime::currentTime()<<"MyClass: onPushButtonClickedRequestCompleted request completed";
if (reply->error() != QNetworkReply::NoError)
{
qDebug() << "Error in" << reply->url() << ":" << reply->errorString();
this->setCursor(Qt::ArrowCursor);
return;
}
QByteArray data = reply->readAll();
QPixmap pixmap;
pixmap.loadFromData(data);
int width;
int height;
//application size can be changed
QRect rec = QApplication::desktop()->screenGeometry();
height = rec.height();
width = rec.width();
qDebug()<<QTime::currentTime()<<width<<","<<height;
QSize *size = new QSize(width,height);
if(size)
{
QPixmap scaledPixmap = pixmap.scaled(*size);
ui.qtImageLabel->setPixmap(scaledPixmap);
}
if(size)
{
delete size;
size = NULL;
}
data.clear();
this->setCursor(Qt::ArrowCursor);
reply->deleteLater();
return;
}
On clicking push button It will send a request to server and will show a different image received from server. It is working fine if it does't exceeds 500 times. If it exceeds that first this error has been shown
QPixmap::scaled: Pixmap is a null pixmap
and it doesn't show the image. Then if someone again sends a request for an image then it shows the following error:
Qt has caught an exception thrown from an event handler. Throwing
exceptions from an event handler is not supported in Qt. You must
re implement QApplication::notify() and catch all exceptions there.
I am not getting what is the error in the above code. Can someone please tell me how to solve this?
The obvious leak is qnam_push_button_clicked_show_image = new QNetworkAccessManager(this);, which doesn't have a balanced delete anywhere. QNAMs should typically created once, then reused for the lifetime of the application rather than created for a single request. So by turning qnam_push_button_clicked_show_image in a class member (same as ui) you'll fix both your leak and improve the efficiency of the code.
That said, I don't think that's what causes your QPixmap error. If you're running this code on X11, then QPixmap is backed by an X Pixmap resource, which is limited by various factors (software and hardware). Even though from your code there's no obvious leak, it could be that repeatedly allocating large pixmaps slowly fragments the memory pool managed by X, up to the point where it can't allocate a block large enough for the scaled pixmap and then triggers the error. Or it could be a driver bug somewhere in the graphics stack. Have you tried if changing the scaled size increases or decreases the limit before it starts breaking? If so, switching to QImage might help relieving the pressure on X.
Aside from that, the code could use some cleanup, especially that superfluous QEventLoop usage. I'm guessing it's a way to prevent the button from being clicked several times until the new image has been loaded, but I'd much rather implement this using button.setEnabled(false) while the image is downloading, because nested event loops combined with network events is a recipe for countless reentrancy issues and hard to debug crashes/bugs.
I'm also confused about why size is allocated on the heap , especially when it's deleted right after, and these if (size) are really confusing, as they can be understood as if (size->isValid()) while what they really mean is if (size != nullptr), which is pretty much guaranteed as the chance of getting an OOM on that line is infinitesimally low. (if you did eventually run out of memory, my guess is it would likely happen in the readAll() or loadFromData() calls above).
ps: good luck pressing that button another 500 times to check if fixing the leak helped ;)

QT 5.5 - QNetworkReply empty data

I already took at others questions but I didn't find an answer.
I have a problem to print HTML code I download with a QNetworkAccessManager.
I need to log into a website to retrieve this code.
I have a slot like this:
void Aims::slotRequestFinished(QNetworkReply* requestReply)
{
QString data = QString(requestReply->readAll());
qDebug() << data;
}
For the first two steps (connection), I can see the HTML code in the console.
The last step doesn't get any data. There is no redirection nor error.
Now, the stranger part is that when I change my code to show the page into a webview, qDebug doesn't show anything, but the code loaded is shown correctly in the webview.
void Aims::slotRequestFinished(QNetworkReply* requestReply)
{
QString data = QString(requestReply->readAll());
qDebug() << data;
ui->webView->setHtml(data);
}
Well, I can save the content into a file. But I would really like to understand why I can't see anything in qDebug

QWebView not showing page when JS involved

I successfully managed to compile Qt 4 including WebKit for WinCE. QWebView seems to run fine - I can load a HTML5 document and it gets displayed.
ui.webView->page()->settings()->setAttribute(QWebSettings::JavascriptEnabled, true);
ui.webView->setUrl(QUrl::fromLocalFile(QFileInfo(QLatin1String("test.html")).absoluteFilePath()));
However, as soon as the page contains any JavaScript (even an empty script-tag already causes the problem), QWebView will only display a blank page.
The QWebInspector window can also not be shown, as it also just displays a blank window.
I doubt this is a common problem, so my question is, how I could dig into that issue. Is there any debug log for QWebView?
Unfortunately, there's no exception or assertion failure being thrown while execution.
Any ideas? :)
Thank you in advance.
EDIT:
Here is the test code creating the problem. The first four lines of loadFinished are some test code to check valid pointers and whether I could call methods on QWebFrame at all. All code lines execute well until the evaluateJavaScript, where I get an access violation.
I could not post the HTML code inside setHtml, seems to be forbidden by Stackoverflow.
ce0::ce0(QWidget *parent, Qt::WFlags flags)
: QMainWindow(parent, flags)
{
ui.setupUi(this);
connect(ui.webView, SIGNAL(loadFinished(bool)), SLOT(loadFinished(bool)));
ui.webView->page()->settings()->setAttribute(QWebSettings::LocalContentCanAccessRemoteUrls, true);
ui.webView->page()->settings()->setAttribute(QWebSettings::LocalContentCanAccessFileUrls, true);
ui.webView->page()->settings()->setAttribute(QWebSettings::DeveloperExtrasEnabled, true);
ui.webView->page()->settings()->setAttribute(QWebSettings::JavascriptEnabled, true);
//ui.webView->setUrl(QUrl::fromLocalFile(QFileInfo(QLatin1String("test.html")).absoluteFilePath()));
ui.webView->setHtml(...);
}
void ce0::loadFinished(bool ok) {
QWebPage* p = ui.webView->page();
QWebFrame* f = p->mainFrame();
QString qs = f->title();
bool x = ui.webView->page()->settings()->testAttribute( QWebSettings::JavascriptEnabled );
f->evaluateJavaScript("document.getElementById(\"content\").innerHTML = \"Whatever\";");
}

Direct Show 9 phonon Error "Pins cannot connect"

I'm getting the following error when trying to use the Direct Show 9 backend with qt's phonon framework:
Pins cannot connect due to not supporting the same transport. (0x80040266)
Does anyone know what this error means and/or how to fix it? Is this a problem with the Direct Show 9 backend for phonon?
Apparently the problem has to do with bad metadata. If the Id3 tags aren't just right, the direct show 9 backend chokes on them. I solved the problem by writing the following function:
void removeTags(UDJ::DataStore::song_info_t& song){
static int fileCount =0;
if(song.source.fileName().endsWith(".mp3")){
UDJ::Logger::instance()->log("On windows and got mp3, copying and striping metadata tags");
QString tempCopy = QDesktopServices::storageLocation(QDesktopServices::TempLocation) + "/striped" + QString::number(fileCount) +".mp3";
if(QFile::exists(tempCopy)){
UDJ::Logger::instance()->log("Prevoius file existed, deleting now");
if(QFile::remove(tempCopy)){
UDJ::Logger::instance()->log("File removal worked");
}
}
bool fileCopyWorked = QFile::copy(song.source.fileName(), tempCopy);
if(!fileCopyWorked){
UDJ::Logger::instance()->log("File copy didn't work");
return;
}
TagLib::MPEG::File file(tempCopy.toStdString().c_str());
file.strip();
file.save();
Phonon::MediaSource newSource(tempCopy);
song.source = newSource;
if(fileCount == 3){
fileCount =0;
}
else{
fileCount++;
}
}
}
song_info_t is just a struct with a Phonon::MediaSource member in it called source. The function works by using taglib to strip off all of the metadata for a song and save the new song as a temporary file. The function also rotates the filename is uses for the temporary file so that it doesn't create an infinite number of temporary copy files. I hope this helps anyone else who is having this error.

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