UnigramDev/Unigram/settingsbutton-disabled • 0b6ba98 • 1 files, +4/-5
Don't animate a deferred template part from SettingsButton's Disabled state

SettingsButton's Disabled visual state animated the Foreground of three template
parts, one of which -- DescriptionPresenter -- is x:Load="False" and is only
realized by OnApplyTemplate when Description is non-empty. A Storyboard whose
TargetName cannot be resolved fails with E_INVALIDARG, and because the initial
visual state is applied while the template is being applied, that is inside the
control's measure. The ArgumentException therefore surfaces from the measure of
whatever is above it, which is why the reported stacks anchor on
HeaderedControlPanel and SettingsPanel and name nothing closer to the cause.

It needs the button to be disabled before its template is applied, which is what
happens when the disabled state is inherited: on Settings > Power saving the
HeaderedControl carries IsEnabled, so its SettingsExpanders -- whose ActionButton
has no Description -- are born disabled. Settings > Data and storage has the same
disabled expanders but sets Description, so the part is realized and the target
resolves. Reported by crash telemetry on every version from 12.4.1 to 12.9.1.

Dropping the key frame is enough: DescriptionPresenter is already painted with
SystemControlDisabledChromeDisabledLowBrush, so the disabled appearance is
effectively unchanged.

Checked the rest of the app for the same shape: this is the only
Storyboard.TargetName in any template that points at an x:Load="False" element.
The VisualState.Setters that target deferred parts (RecentChoosers in the message
reaction templates) are left alone -- those resolve differently and do not throw,
as reactions demonstrate every day.

Not built: no UWP/.NET Native build environment here. The file was checked for XML
well-formedness.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

#unigram