[Perf] Reuse ElementEventArgs in tree propagation#34134
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Pull request overview
Improves Microsoft.Maui.Controls.Element descendant add/remove event propagation performance by reusing a single ElementEventArgs instance while walking up the parent chain, instead of creating new args at each propagation step.
Changes:
- Create
ElementEventArgsonce inOnDescendantAdded(Element)/OnDescendantRemoved(Element)and pass it through a new helper overload during parent propagation. - Update propagation to call
RealParent?.OnDescendantAdded(args)/RealParent?.OnDescendantRemoved(args)to avoid repeated allocations while walking ancestors.
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| void OnDescendantAdded(ElementEventArgs args) | ||
| { | ||
| DescendantAdded?.Invoke(this, args); | ||
| RealParent?.OnDescendantAdded(args); | ||
| } |
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Introducing an overload OnDescendantAdded(ElementEventArgs args) makes it easy to accidentally call the allocating OnDescendantAdded(Element child) in future edits, and it’s less discoverable that one overload is the non-allocating propagation helper. Consider renaming the helper overload to something like OnDescendantAddedCore/OnDescendantRemovedCore for clarity and consistency with other *Core helper patterns in this file.
This was referenced Feb 19, 2026
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LGTM from my review. I don't see blocking issues; this looks good to merge as-is.
StephaneDelcroix
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Feb 23, 2026
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/azp run maui-pr-uitests, maui-pr-devicetests |
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🚀 Dogfood this PR with:
curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34134Or
iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34134" |
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Fixes #34093 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
- Defer ElementEventArgs creation until first non-null subscriber - Zero allocations when no DescendantAdded/Removed handlers exist - Rename recursive helpers to OnDescendantAddedCore/RemovedCore Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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@PureWeen @mattleibow could you please have a look at this PR and let me know what you think about it? could we merge this into net11.0 soon? |
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/azp run maui-pr-uitests,maui-pr-devicetests |
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Remove '?' from ElementEventArgs parameters in OnDescendantAddedCore and OnDescendantRemovedCore. The file has '#nullable disable' at the top, so nullable reference type annotations are invalid and cause CS8632 warnings which become errors when TreatWarningsAsErrors=true (e.g. in dotnet/android CI). Introduced in #34134. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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…t in Element.cs (#34751) <!-- Please let the below note in for people that find this PR --> > [!NOTE] > Are you waiting for the changes in this PR to be merged? > It would be very helpful if you could [test the resulting artifacts](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you! ## Description Removes `?` nullable annotations from `ElementEventArgs` parameters in `OnDescendantAddedCore` and `OnDescendantRemovedCore` in `Element.cs`. The file starts with `#nullable disable`, so nullable reference type annotations are invalid and produce **CS8632** warnings. MAUI CI sets `TreatWarningsAsErrors=false` so these pass silently, but downstream consumers like **dotnet/android** build with `TreatWarningsAsErrors=true`, causing build failures. Introduced in #34134. ## Fix Simply remove the `?` from the `ElementEventArgs` parameter types. Under `#nullable disable`, reference types are already implicitly nullable, so the behavior is unchanged. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!
Fixes #34093
Description
OnDescendantAddedandOnDescendantRemovedallocate a newElementEventArgsat every tree level during parent propagation. This creates O(depth) allocations per child add/remove. This PR creates theElementEventArgsonce at the entry point and passes it up through the recursive walk.