API doc clarification request: if a key is not provided for a widget, what is default key? #13787

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1. sethladd

   added

   d: api docsIssues with https://api.flutter.dev/Issues with https://api.flutter.dev/

   on Dec 28, 2017
2. sethladd

   changed the title [-]API doc clarification request: if a key is not provided for a widget, what happens?[/-] [+]API doc clarification request: if a key is not provided for a widget, what is default "key"?[/+] on Dec 28, 2017
3. Hixie commented on Jan 2, 2018

   

   Hixie

   on Jan 2, 2018

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   The default key is null, i.e. no key.
4. Hixie commented on Jan 2, 2018

   

   Hixie

   on Jan 2, 2018

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   Also we could add the following when adding docs to keys:

   Basically any time you're building a list of widgets from a list of data, and the list might change, you should key the children, so that we keep the subtrees tied to the data. Otherwise, we won't know what's going on and if anything is stateful the state could spill from one to the other (what's really going on is that the data is spilling from one to the other -- we have no way to distinguish "each item changed its data" from "one of the items was removed/added and pushed all the other items around" without keys).

   Generally the best key to use is a ValueKey where T is the type of the data you're generating the widgets from, assuming that each such datum is unique. (In particular, no need to use toString.)

   ❤️React with ❤️1Reacted by Pedro Massango
5. Hixie

   added this to the 4: Next milestoneThis milestone has been deleted milestone on Jan 2, 2018
6. wmleler commented on Jan 2, 2018

   

   wmleler

   on Jan 2, 2018

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   Several people (including at least one flutter team member) have been bitten recently by the confusion mentioned by Ian. Would be nice to add language like his to the docs sooner rather than later.
7. zoechi

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   frameworkflutter/packages/flutter repository. See also f: labels.flutter/packages/flutter repository. See also f: labels.

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8. csells

   changed the title [-]API doc clarification request: if a key is not provided for a widget, what is default "key"?[/-] [+]API doc clarification request: if a key is not provided for a widget, what is default key?[/+] on Jan 13, 2020
9. kf6gpe

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   P2Important issues not at the top of the work listImportant issues not at the top of the work list

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10. pedromassangocode commented on Jul 22, 2020

    

    pedromassangocode

    on Jul 22, 2020

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    Found in the current docmunetation because it does not state what it the default key value when not provided.

    I looked at the following links:
    https://docs.flutter.io/flutter/foundation/Key-class.html
    https://docs.flutter.io/flutter/widgets/Widget/key.html
11. pedromassangocode

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    found in release: 1.17Found to occur in 1.17Found to occur in 1.17

    found in release: 1.21Found to occur in 1.21Found to occur in 1.21

    has reproducible stepsThe issue has been confirmed reproducible and is ready to work onThe issue has been confirmed reproducible and is ready to work on

    on Jul 22, 2020
12. Hixie

    removed this from the None.This milestone has been deleted milestone on Aug 17, 2020
13. danagbemava-nc commented on Nov 1, 2022

    

    danagbemava-nc

    on Nov 1, 2022

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    The current documentation does not state which key is used either.

    I checked the following links:
    https://api.flutter.dev/flutter/widgets/Widget/key.html
    https://api.flutter.dev/flutter/foundation/Key-class.html
14. danagbemava-nc

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    found in release: 3.3Found to occur in 3.3Found to occur in 3.3

    found in release: 3.5Found to occur in 3.5Found to occur in 3.5

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    found in release: 1.17Found to occur in 1.17Found to occur in 1.17

    found in release: 1.21Found to occur in 1.21Found to occur in 1.21

    on Nov 1, 2022
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    AbdeMohlbi

    on May 11, 2026
17. auto-submit

    closed this as completedin #185197on May 28, 2026
18. pull

    added a commit that references this issue on May 28, 2026

    document that the default Key is null and explain proper usage in lis…

    ...

    This issue will close once commit ba09ef4 is merged into the 'master' branch.

    ba09ef4
19. via-guy

    added a commit that references this issue on Jun 26, 2026

    document that the default Key is null and explain proper usage in lis…

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    This issue will close once commit 544a79f is merged into the 'master' branch.

    544a79f
20. github-actions commented on Jul 14, 2026

    

    github-actionsbot

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    This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.
21. github-actions

    locked as resolved and limited conversation to collaborators on Jul 14, 2026