[Interest] (Q)Plugins and QML/Quick

Rui Oliveira ruilvo at hotmail.com
Tue Sep 14 20:00:24 CEST 2021

PS: For reference, I'm talking about what would be the QML/Quick 
equivalent of the Plug and Paint example:


Where the plugins bring UI components with themselves.

Às 18:24 de 14/09/2021, Rui Oliveira escreveu:
> Hey,
> I think we're speaking about different things. I've explored a bit and 
> it seems that it's typical to create QML modules/plugins to expose new 
> QML types that are found at runtime. But you still explicitly use 
> those types. Like, an external project will add the 
> "MyAwesomeAlgorithm" type and you can use that in your application's QML:
> ```
> import <plugin.uri>
> MyAwesomeAlgorithm
> {
>    id: "myAwesomeAlgo
> }
> ```
> But my goal is to not know about the types beforehand at all. It's 
> basically the "copy the dll to the application folder and it'll 
> magically show up as an option" pattern. The goal is to provide an 
> extensibility framework, like eclipse, or web browser addons. Not just 
> using a type defined elsewhere.
> This is more or less what I mean: 
> https://stackoverflow.com/questions/66618613/qml-c-classes-with-bring-your-own-component
> Thanks,
> Rui
> Às 10:02 de 14/09/2021, Ulf Hermann escreveu:
>>> Maybe I missed something, but this seems more like a solution to 
>>> manage QML resources and modules that you know about at compile time.
>> The QML import path allows you to combine modules compiled separately 
>> in the context of different projects.
>>> I'm talking about a runtime problem. Lemme try to explain with some 
>>> simplified code. Allow me to leave a link to some markdown and 
>>> syntax highlighted stuff:
>>> https://gist.github.com/ruilvo/43365e67f6d3ea472531738fd5a52793
>> Do not start with something as low level as a plugin. Think of your 
>> code as logical units, defining different parts of your UI. Then 
>> create a QML module for each. The plugins are automatically 
>> generated. You don't have to care about them. Using "import 
>> Some.Module" in QML will load them as necessary.
>> You only need to make sure the QML engine knows about the relevant 
>> import paths. If you use the default directory layout as shown in the 
>> blog post, the default import path will be enough.
>> Otherwise you have to call QQmlEngine::addImportPath(). This is 
>> likely what you have to do if you want to combine modules from 
>> different projects.
>> You say that "import mytype" is not possible. However, there must be 
>> some starting point in your application. You need to have code that 
>> specifies a first plugin to load by file name. This can instead be 
>> phrased as a module URI. If you insist on not having an entry point 
>> main.qml, you can dynamically generate a two-line QML document and 
>> load it via QQmlComponent::setData():
>> // given moduleName and elementName:
>> QQmlEngine engine;
>> engine.addImportPath( ... );
>> QQmlComponent component(&engine);
>> const QString qml = QStringLiteral("import %1\n%2{}").arg(moduleName, 
>> elementName)
>> component.setData(qml.toUtf8(), QUrl());
>> QObject *myQmlObject = component.create();
>> best regards,
>> Ulf
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