qtqt5can-bussocketcanqtplugin

Custom plugin for qt is not loaded. How to debug?

I wrote a custom plugin for QCanBus, that simply is a copy of the socketcan plugin but has been renamed and the identifiers have been adjusted to that new name.

I did that copying to first get the plugin recognised before I alter it.

I changed the qmake project to look that way:

TEMPLATE = lib
TARGET = qtcopysocketcanbus
CONFIG += plugin
QT = core serialbus

HEADERS += \
    copysocketcanbackend.h

SOURCES += \
    main.cpp \
    copysocketcanbackend.cpp

DISTFILES = plugin.json

and added the plugin.json like so:

{
    "Key": "copysocketcan"
}

I then renamed everything else from socketcan to copysocketcan in the main.cpp, the copysocketcan.cpp and the copysocketcan.h as well.

When I build the project, I get my *.so file which i put into $QT_PLUGIN_PATH/canbus/ on my target.

However, a quick start reveals, that qt only lists the plugins that came with the installation, not my added custom one.

I tried putting QLoggingCategory::setFilterRules(QStringLiteral("qt.canbus* = true")); as first line in my code and hoped getting more debug output, but I only get the debug output that my own application is producing. No output from the actual QCanBus.

So my questions are

  1. How to enable the debug output for qt.canbus? Do I have to build QT with debug config for that?
  2. Does my approach for creating a plugin reasonable?
  3. Any ideas, why the custom plugin is not listed?
Solution

  • Through a helpful comment, I was able to debug the problems. The commentor suggested to use QT_DEBUG_PLUGINS to debug the plugin call. That lead to the appearance of an error message, that clearly stated, that the plugin I was trying to load because it was not a plugin and plugin metadata could not be extracted.

    A bit of googling after those messages helped.

    The answer to question 1 is:

    Yes, you apparently have QT to build with debug information, to get the actual log output. In my case, I configured the framework with --force-debug-info

    For the second question, my approach was indeed reasonable, because as answer for question 3 turned out that one has to include the moc file as soon, as a Q_OBJECT macro is used within a *.cpp file and not in a separate header, which is the case for the canbus plugins. You can read more about that here