QtCS25 - Using Qt Quick with other programming languages

Session Summary

Presentation by Vladimir and Discussion

Session Owners

Vladmir Minenko

Fabian Kosmale

Notes

Roadmap see Vladimir's slides.

• .Net, Java, Rust, Swift, Python covered
• What to do about JavaScript? Needs more research
• People ask about Go
• Maybe network-based transport between Qt Quick and other language? REST, OpenAPI?

How does it actually work?? Can we have an example?

Python as example:

• Bridge exports a single funtion
• Function accepts a Python container
• Makes it available in QML, via reflection, as a singleton (or QAbstractItemModel? or some property?)
• Idea:
  • Provide small library
  • Use native types from respective language
  • Do language-dependent magic to transform data for QML
    • Rust: procedural macros
    • Python, Java, Swift: reflection
    • C#: don't know yet (currently generating C++ code)
  • expose limited subset of data to QML

How does this interact with tooling/qmlcachegen etc?

• We can't do all the type registration at run time (but how else? and what is build time even?)
• Compilation to C++ is probably not a good idea
• Optimized byte code compilation might work

What about other QML modules? Can they be used? For example QtMultimedia

• Can use everything exposed to QML
• Custom rendering probably not

What is the use case?

• Qt-owned UI with different host language
• For Python piggy-back on Qt for Python
• For Rust piggy-back to CXX-Qt
• No combining with other frameworks for now
  • Embedding is a different project, for example see android

What types will be available?

• Some primitive types: string, url, numbers, etc
• No custom QQuickItem for now (that would be full bindings)
• Maybe simple QObject-derived types
• We hope that only exposing data (value types) is enough

What IDE will be used? Qt Creator or the language-specific one?

• We don't know yet
• We want to support language-native IDEs
• We need to generalize our QML tooling (not only qmlls, but also profiler or debugger)

Does data need to be copied when moving between other language and QML?

• Depends on host language
• Python has dictionaries; hopefully we can use them to back JavaScript objects in QML

Would you be able to mix e.g. Qt for Python with the python bridget?

• With python and rust, probably
• Not with swift because we don't have full bindings
• With probably yes, using QtJambi

Need to expand QML API of QtQuick to prevent the urge to use C++ API

Can you use multiple different bridges in one app?

• Nobody brought this up yet. We don't know yet.
• What about moving data from one backend language to another via QML?

What about performance?

Presentation Slides