Theme: C++ implementation based on propagated attached property #19316
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micieslak
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Awesome work! I love it :beers
Let's get it merged quickly now that we have the release branch. It's probably a burden to maintain.
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Awesome work! Just some suggestions and minor things
| readonly property alias monoFont: monoFont.font | ||
| readonly property alias codeFont: codeFont.font | ||
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| FontLoader { |
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We could (pre)load all these fonts from C++ too, and it would be faster imo :) And just expose the three baseFont/monoFont/codeFont properties
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I meant https://doc.qt.io/qt-6/qfontdatabase.html#addApplicationFont
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The idea was to keep the attached type as small/simple as possible. Ideally only stuff that can benefit from propagation should be there. I found it more modular when keeping things like that separated.
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Yup, this wouldn't be part of the propagation, just initialized and setup somewhere else, not in QML
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Great work on this implementation! The structure looks solid and the overall approach makes the theming system feel clean and easy to work with. I’ve left a couple of comments and suggestions, but everything is looking really good.
Next step for me will be to run a full test of the PR on both desktop and mobile to ensure everything behaves correctly across breakpoints.
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@micieslak, could we postpone merging this PR until a big tokens-related refactor gets merged? |
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Great work, let's merge this 🚀
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This was referenced Dec 10, 2025
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What does the PR do
Re-implements
Themefrom stateful singleton to attached property object, with dynamically propagated properties through the visual objects tree.The approach is similar to the one used by buit-in themes, like
MaterialorUniversal.It consists of following elements:
Theme- attached property type, holds state (padding, font size offset, style), which is propagated within the objects tree.StatusColors- singleton, stateless, holds fixed colors definitionsThemePalette<- non-mutable, not creatable component served byTheme, defining colors. We have two instances for dark/light stylesThemeUtils- singleton, stateless utility methods and constantsFonts- singleton, stateless, loads and serves fontsAssets- singleton, stateless, access point for png/svg/emojiBy using attached property type, visual features like colors and sizes are no longer single global state, the same for all components within the app. It brings better flexibility when building responsive layouts for multiple platforms.
Closes: #19213
Affected areas
Entire QML codebase
Architecture compliance
My PR is consistent with this document: QML Architecture Guidelines
Impact on end user
This change doesn't bring any changes visible to the end user.
How to test
Run the app and go through all possible views to detect incorrect colors, fonts, paddings, etc.
Risk
As there are many changes, there is a risk of introducing regressions related to visual appearance.