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I have the community edition 10.3 of Delphi on Windows 10 and trying to use the JEDI (JVCL v3.50) TJvHidDeviceControllerClass (v 1.0.35) to control my HID device in a VCL form application. This exception also gets thrown when I start up Delphi and when closing it down showing a dialog, provided that the component is already present on the form when loading the project. When ran with the OnDeviceCreateError() event handler assigned, the application behaves OK as I set the debugger to let the application handle this particular exception and setting the "Handled" boolean to true inside the OnDeviceCreateError() handler. It also works fine when run outside the Delphi GUI.

I have been searching for clues about fixing this issue and have seen that other people have encountered it as well. As most of the posts about this is quite old I wonder if I don't have the correct version of the library (https://github.com/project-jedi/jvcl). The JEDI library was fetched from github just a week ago using the instructions on the readme page. My local repo was cloned from the master branch. I built it and installed it locally with no hassle.

Albeit working fine when running the application this exception is a bit of a nuisance as it messes with the Delphi GUI itself during startup (the exception dialog is shown, parts of the GUI goes missing after clicking OK).

I don't think that my code is the culprit here as the problem presents itself before any application code has even begun executing. I suspect that Delphi itself runs the constructor for the component before the OnDeviceCreateError() handler has been assigned and so the exception propagates all the way up to the GUI during palette placement or startup. Why the exception shows while shutting Delphi down is harder for me to explain.

Is there a fix to this or a setting to prevent Delphi running the constructor at design time?

Should I create the TJvHidDeviceControllerClass instance during form creation instead?

Thanks in advance /Thom

Ivan Yuzafatau
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Captain-sq
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1 Answers1

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After some trial and error I worked around the problem by removing the component from the form designer and adding the TJvHidDeviceControllerClass manually with method bindings to the class in code instead.

The default constructor should not be used as it does not bind the exception handler at create time. Use the other one that does the binding. It now works fine without stray exceptions at start/stop times. When creating manually, be shure to explicitly free the TJvHidDeviceControllerClass object instance at form close.

Captain-sq
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