macOS: how to show NSPanel after a qdialog has been closed?

gvanvoor

I need to show an NSPanel (so using some cocoa code) after a qdialog has been closed. When doing so my NSPanel is shown but immediately dismissed.
I looked at qcocoafiledialoghelper.mm to see how it's done there and found the following promising piece of (documented) code:

// Call processEvents in case the event dispatcher has been interrupted, and needs to do
// cleanup of modal sessions. Do this before showing the native dialog, otherwise it will
// close down during the cleanup.
qApp->processEvents(QEventLoop::ExcludeUserInputEvents | QEventLoop::ExcludeSocketNotifiers);

But unfortunately that doesn't help in my case.
There's a second call in qcocoafiledialoghelper.mm before the native panel is shown:

// Make sure we don't interrupt the runModal call below.
QCocoaEventDispatcher::clearCurrentThreadCocoaEventDispatcherInterruptFlag();

but that's one I can't call from my code as it uses some Qt internal private stuff.

Any ideas on how to get this working?

jsulm

@gvanvoor said in macOS: how to show NSPanel after a qdialog has been closed?:

When doing so my NSPanel is shown but immediately dismissed

Can you show your code?
Sounds like your NSPanel is going out of scope because it's a local variable (just an idea).

gvanvoor

Not going out of scope:

@autoreleasepool
{
    MyPanel * thePanel = [ [ MyPanel alloc ] init ];
    qApp->processEvents( QEventLoop::ExcludeUserInputEvents | QEventLoop::ExcludeSocketNotifiers );
    auto theResponse = [ thePanel runModal ];
    if( theResponse == NSModelResponseOK )
    {
    }
}

the runModel call returns immediately (while it should be blocking) and theResponse == NSModalResponseStop.

SGaist

Hi,

You need to provide an MRE so people can test your code on their own to help debug it.

gvanvoor

@SGaist I'm assuming MRE stands for a minimal code example that exhibits the problem?

gvanvoor

I wasn't able to reproduce the problem in a minimal example, but after a lot of digging I finally found the culprit: a worker thread is invoking QCoreApplication::postEvent which somehow causes my panel to close.

SGaist

Glad you found out and thanks for sharing !

What event did you post ?

gvanvoor

@SGaist A custom event. I don’t know if that gets sent through the Cocoa event loop, but I guess it does and assume Cocoa stops the modal panel to be able to process the event in the main event loop.