How to use a QT QML C++ plugin in another application?

Question

I'm trying to wrap my head around QML plugins and I hope that someone can explain it to me because I seem to be missing something.

So I've gone ahead and created a Qt Quick 2 Extension Plugin. I have a simple source file, I've subclassed the QQmlExtensionPlugin class and registered the new type with qmlRegisterType. I've built this project and it gives me a DLL (I'm on Windows 7, and using QT 5.13). As I understand it, I should now be able to take this DLL and the qmldir file and drop into a new project and I should be able to load the QML from the DLL that is exposed via the qmldir file.

Unfortunately, when I do that, it doesn't work. All the examples I'm seeing online are showing a qml file that does an import of the plugin qml, but every time I try that, the import doesn't work and gives me a "QML module not found" error.

So my question is: How do I actually use the DLL and qmldir files in another project to expose the QML from the DLL to the new project?

Answer 1

It seems that you're missing the root QML import path.

The default root import path is %QTDIR%/qml, you can simply copy&paste your plugin modules into this folder so that the QML engine can find and load it.

Or a more common practice, using QQmlEngine::addImportPath()

QQmlEngine engine;
engine.addImportPath(qApp->applicationDirPath() + "/qml");

Note that you should always use Module (Namespace) Imports to import your C++ plugin module:

import My.CppModule 1.0

Using Directory Imports to import a C++ plugin module is a Undefined Behavior currently:

import "My/CppModule" // Might fail