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POQT QDialog not hiding properly when show/hide called quickly
 

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    <p>I have a QDialog on my main thread and I have some logic that happens on a separate thread. When the logic begins, a signal is emitted connected to show() on the dialog. When the logic ends, a signal is emitted that is connected to hide() on the dialog. When the logic actually does work, the dialog is show/hide properly. If the logic does "nothing" and the signals are just emitted sequentially, the dialog doesn't always show/hide properly.</p> <p>My connections are made similar to this:</p> <pre><code>class MainWindow : public QMainWindow { Q_OBJECT public: MainWindow(QWidget* parent = 0) : Ui(new Ui::MainWindowUi), Transferer(new DataTransferer()), TransferProgress(this), TransferThread() { Ui-&gt;setupUi(); connect(&amp;Transferer, SIGNAL(Begin()), &amp;TransferProgress, SLOT(show())); connect(&amp;Transferer, SIGNAL(End()), &amp;TransferProgress, SLOT(hide())); Transferer.moveToThread(&amp;TransferThread); TransferThread.start(); Transferer.DoStuff(true); } virtual ~MainWindow() { TransferThread.quit(); TransferThread.wait(1000); delete Ui; Ui = NULL; } private: Ui::MainWindowUi* Ui; DataTransferer Transferer; TransferProgressDialog TransferProgress; QThread TransferThread; } </code></pre> <p>The logic looks similar to this:</p> <pre><code>class DataTransferer : public QObject { Q_OBJECT public: DataTransferer(QObject *parent) : QObject(parent) {} virtual ~DataTransferer() {} void DoStuff(bool dontDoStuff) { emit Start(); if (!dontDoStuff) { QThread::sleep(1); } emit End(); } } </code></pre> <p>When the DataTransferer does stuff, everything works fine. When the dialog is shown and hidden in rapid succession, I get the ghost dialog approximately every other time I call DoStuff().</p> <p>I used QThread::currentThreadId() and verified that the dialog and logic are running on separate threads.</p> <p>Why would my dialog not hide properly in this case? Should I just force my logic to always run for at least a few hundred milliseconds (that solution is bad)? Is there a way I can have my dialog make sure it's fully loaded before trying to hide itself? Should I handle these signals/slots differently?</p> <p>EDIT: I've currently resigned to just putting a QThread::sleep(1) after I emit the signal to show() the dialog. I don't like this solution, but nothing else has seemed to work. The sleep(1) allows the dialog to come all the way up before hiding it. I was also able to get this to work with QThread::msleep(10), but that still resulted in the ghost dialog about 1 in 6 tries.</p> <p>I tried using a member QMutex in the dialog logic whenever I called either show() or hide(), but this didn't work.</p> <p>I changed all cross-thread connections to use Qt::BlockingQueuedConnection and Qt::QueuedConnection and neither attempt was successful.</p> <p>I tried moving the slot connections from the dialog to the object that sets up the connections and then calling the slots directly, but that didn't prove successful either.</p>
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