I cannot stress this enough but I have looked as far as I can over the internet for a solution and either they didn't have a solution or all they did was add a support ticket. The problem is that after creating a python qt quick application I try opening the QML file but when I go to the design tab it give me this error:
The Designer is very finicky and can crash for various reasons. I've had success seeing the actual errors causing this dialog by launching Creator from the command line with debugging enabled:
QT_LOGGING_RULES="qtc.nodeinstances.init.debug=true" "/Applications/QtCommercial/Qt Creator.app/Contents/MacOS/Qt Creator"
That's specific to macOS but the like approach should work on any OS.
Look for error messages related to "Puppet". That's the name of the subprocess that actually renders the QML for Designer.
You can also go to Preferences -> Qt Quick -> QML Emulation Layer and try the opposite of the current setting and see if it works any better.
The solution that works for me is as follows:
OS: windows 10
Go to Tools >> Options >> Qt Quick >> (tab) Qt Designer
In the "Use fallback QML emulation layer", you see the placeholder path there. Switch it to C:\Qt\Tools\QtDesignStudio\bin or use browse if you have a different install location for Qt such that path\to\QtDesignStudio\bin
Boy do I have a FIX for you guys. I had been screwing around with this same issue to no avail, until I came across an error that wouldn't let me download qt3d (something) and I know that was part of the installation choices so I decided to uninstall everything. A thing to note when uninstalling: the Maintenance Tool doesn't uninstall everything. There were still Qt files located in C:\Users\user\AppData\Roaming I needed to delete those. Also, I needed to go into the Registry Run >>> Regedit >>>> Edit >>> Find >>> then search for Qt and that brought up all of the QT keys that still remained. I just deleted them one by one. For the Reinstall I practically installed everything (within reason) here's the list of my installation selections. Happy Hunting Fellow Qt'errr's!
Qt 5.15.2
Developer and Designer Tools
License: I chose L GPL I chose Cmake not qmake