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QtCS25 - Using Qt Quick with other programming languages

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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

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