[Interest] QQmlExtensionPlugin not loading

[Jesper Huijgens]

Hello,

First of all. Thanks for the help so far, got me quite a bit further.

What I try to achieve is having plugins that can inject e.g. a button on 
a toolbar. Simply put: an application that can be extended via plugins.
During development I do not know what plugins there will be at runtime. 
So I do not know what to import in Main.qml.
All plugins also implement an interface I made with a method /initPlugin/.
In this method the plugin can create a qml object and inject it into the 
already running UI (Calling this method is triggered from within the 
main UI).

Easiest/simplified example would be:

--------------------
*MyPlugin.cpp*:
     void MyPlugin::registerTypes (const char* uri) // uri => "MyPlugin"
     {
         qmlRegisterType<MyPluginType>(uri, 1, 0, "MyPluginType");
     }

     void MyPlugin::initPlugin (QObject* objectInsideTheRunningUI)
     {
         QQmlEngine* engine = 
QQmlEngine::contextForObject(objectInsideTheRunningUI)->engine();
         auto newButton = createButtonUsingEngine(engine, 
"MyPluginButton.qml"); // Method creating QQmlComponent, and calling 
QQmlComponent.create() on it
     }

*MyPluginButton.qml*:
import QtQuick 2.10
import MyPlugin 1.0 // *Here I get module MyPlugin is not installed.*

Item {
     MyPluginType {}
}
--------------------

TL;DR:
     If I import my plugin module in Main.qml it works like a charm.
     If I dynamically create a qml object which call the same import 
call (import MyPlugin 1.0) it does not work. I get module MyPlugin is 
not installed.

In tried calling the registerTypes method inside initPlugin. This seems 
to work. But I am curious why it works if I call import in Main.qml and 
not in MyPluginButton.qml, and what I should do to make it work.

Thanks.

Kind regards,
Jesper

On 09-03-18 14:53, Jesper Huijgens wrote:
> Ok, I see what the problem is.
>
> I expected Qt to automatically register the types. Even without the 
> import statement.
>
> --
> Jesper
>
> On 09-03-18 14:44, Martin Leutelt wrote:
>>
>> *From: * Jesper Huijgens <jesper.huijgens at sioux.eu>
>> *To: * <interest at qt-project.org>
>> *Sent: * 3/9/2018 2:24 PM
>> *Subject: * Re: [Interest] QQmlExtensionPlugin not loading
>>
>>     With QML_IMPORT_TRACE I see again the right folders. But I do not
>>     see any attempt of loading the plugin.
>>
>>
>> You're missing an import statement in your main.qml to load your 
>> plugin (see http://doc.qt.io/qt-5/qtqml-modules-cppplugins.html).
>> addPluginPath()/addLibraryPath() isn't necessary for QML plugins, but 
>> (depending on your project hierarchy or how your application is 
>> installed/deployed) you might need addImportPath().
>>
>>
>>
>>     Kind regards,
>>     Jesper
>>
>>
>> Regards
>> Martin
>>
>>
>>
>>     On 09-03-18 14:20, Martin Leutelt wrote:
>>>
>>>     *From: * Jesper Huijgens <jesper.huijgens at sioux.eu>
>>>     <mailto:jesper.huijgens at sioux.eu>
>>>     *To: * <interest at qt-project.org> <mailto:interest at qt-project.org>
>>>     *Sent: * 3/9/2018 2:04 PM
>>>     *Subject: * [Interest] QQmlExtensionPlugin not loading
>>>
>>>         Hi all,
>>>
>>>         For our project we see that QQmlExtensionPlugins are not
>>>         loaded.
>>>         I made a very basic example project that creates a
>>>         QQmlExtensionPlugin
>>>         and an application that should use. The plugin, with the
>>>         corresponding
>>>         qmldir, are placed in a plugin subdir in the output
>>>         directory of the
>>>         application.
>>>         The application sets both libraryPath and pluginPath. I
>>>         output the
>>>         pluginPathList(), I see what I think are the correct folders
>>>         on the
>>>         debug output.
>>>
>>>         I placed a qDebug() in registerTypes of the plugin. I see
>>>         nothing on the
>>>         debug output.
>>>
>>>         Setting QT_DEBUG_PLUGINS to 1 show me a lot of libraries
>>>         being loaded.
>>>         But not my plugin.
>>>
>>>
>>>     Try QML_IMPORT_TRACE instead, since QT_DEBUG_PLUGINS is for
>>>     debugging plugins for Qt itself, not the QML engine.
>>>
>>>         I work on KDE Neon with g++ 5.4.0, CMake 3.10.0 and Qt 5.10.
>>>
>>>         Kind regards,
>>>         Jesper
>>>
>>>
>>>
>>>     Regards
>>>     Martin
>>>
>>>
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>>>
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>>
>>
>>
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