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@davidhicks980 davidhicks980 commented Oct 4, 2025

_RenderDropdownMenuBody.computeDryLayout accesses this.constraints, but it should only access the constraints parameter passed into computeDryLayout. This PR removes this.constraints access.

image

Also, I removed a line in which the child's offset is being set in computeDryLayout. This appears to be an error:
image

Finally, I'm curious whether there is a reason why only the first child is being used to set the height?

Resolves #176494

Blocking #176494

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@github-actions github-actions bot added framework flutter/packages/flutter repository. See also f: labels. f: material design flutter/packages/flutter/material repository. labels Oct 4, 2025
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Code Review

This pull request correctly refactors _RenderDropdownMenuBody.computeDryLayout to use the constraints parameter instead of this.constraints, adhering to the framework's layout principles. It also removes a side effect within computeDryLayout by no longer setting the child's offset, and simplifies the loop logic. A regression test has been added to ensure computeDryLayout can be called during another render object's layout phase without causing an assertion failure. The changes are sound and improve the correctness and robustness of the DropdownMenu widget's layout logic.

@davidhicks980 davidhicks980 changed the title [material/dropdown_menu.dart] Remove this.constraints access from _RenderDropdownMenuBody.computeDryLayout [material/dropdown_menu.dart] Refactor _RenderDropdownMenuBody.computeDryLayout Oct 4, 2025
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LGTM. Although I wonder why @QuncCccccc wrote it this way in the first place.

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Finally, I'm curious whether there is a reason why only the first child is being used to set the height?

I remember the main purpose of DropdownMenuBody is to determine the text field width. We want the text field width to be the widest menu item width, so we loop through all the items and measure their widths, but feel it's unnecessary to set text field height based on menu item's height. Therefore, only the first child is used to set height. Hope this makes sense:)

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Although I wonder why @QuncCccccc wrote it this way in the first place.

I guess I just copy paste some of the code from performLayout😂

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Thanks for catching this. LGTM

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@QuncCccccc That makes sense! Tbh I didn't know anything about dry layout until I came across this issue, so I'm glad it showed up during testing. I almost never see it in the wild.

I'll go ahead and merge. Thanks both!

@davidhicks980 davidhicks980 added this pull request to the merge queue Oct 18, 2025
Merged via the queue into flutter:master with commit 0161303 Oct 18, 2025
75 checks passed
@davidhicks980 davidhicks980 deleted the dropdown-dry-layout branch October 18, 2025 05:08
engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Oct 18, 2025
auto-submit bot pushed a commit to flutter/packages that referenced this pull request Oct 18, 2025
Roll Flutter from a873a27309b0 to 891d7d539256 (32 revisions)

flutter/flutter@a873a27...891d7d5

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2025-10-18 [email protected] [material/dropdown_menu.dart] Refactor  _RenderDropdownMenuBody.computeDryLayout  (flutter/flutter#176503)
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2025-10-17 [email protected] `SelectableRegion` should use flutter rendered menu on the web for Android and iOS (flutter/flutter#177122)
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...
reidbaker pushed a commit to AbdeMohlbi/flutter that referenced this pull request Dec 10, 2025
…eDryLayout (flutter#176503)

_RenderDropdownMenuBody.computeDryLayout accesses this.constraints, but
it should only access the constraints parameter passed into
computeDryLayout. This PR removes this.constraints access.

<img width="621" height="73" alt="image"
src="https://github.com/user-attachments/assets/495573e3-3b91-4091-8a7c-76594c98e22f"
/>

Also, I removed a line in which the child's offset is being set in
computeDryLayout. This appears to be an error:
<img width="402" height="56" alt="image"
src="https://github.com/user-attachments/assets/0045761d-c958-451b-a6ec-cbdf0fe7bd09"
/>

Finally, I'm curious whether there is a reason why only the first child
is being used to set the height?

Resolves flutter#176494

Blocking flutter#176494

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[material/dropdown_menu.dart] Dropdown body render object accesses this.constraints from computeDryLayout

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