Skip to content

fix(controls): fixes #1670 - TitleBar throws NRE when Collapsed #1671

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
pomianowski merged 3 commits into from
Apr 17, 2026
Merged

fix(controls): fixes #1670 - TitleBar throws NRE when Collapsed #1671

Changes from 2 commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
c48a673
FIX NRE when hovering with mouse over TitleBar buttons if TitleBar is…
luca-domenichini Mar 6, 2026
e361ed6
ADD comment
luca-domenichini Mar 6, 2026
75fa3fb
more null checks and null typed array
luca-domenichini Apr 7, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
3 changes: 2 additions & 1 deletion src/Wpf.Ui/Controls/TitleBar/TitleBar.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -676,7 +676,8 @@ or PInvoke.WM_NCLBUTTONUP

foreach (TitleBarButton button in _buttons)
{
if (!button.ReactToHwndHook(message, lParam, out IntPtr returnIntPtr))
// Check if button is null to avoid potential NullReferenceException if OnApplyTemplate hasn't been called yet, e.g. when TitleBar has Visibility == Collapsed.
if (button == null || !button.ReactToHwndHook(message, lParam, out IntPtr returnIntPtr))
{

Copilot AI Mar 6, 2026

Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

_buttons is declared as TitleBarButton[] but is initialized with null elements until OnApplyTemplate() runs. Adding button == null here fixes the immediate NRE, but it leaves nullability inconsistent and still assumes _buttons contains no nulls in the inner loop (e.g., anotherButton.IsHovered). Consider making _buttons a TitleBarButton?[] (or using an _isTemplateApplied flag / Array.Empty<TitleBarButton>() until templated) and iterating only over non-null buttons to keep the hook logic robust and aligned with nullable reference types.

Copilot uses AI. Check for mistakes.
Comment on lines +679 to 681

Copilot AI Mar 6, 2026

Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Please add a regression test for the reported scenario (TitleBar Visibility=Collapsed + mouse hover over the window) to ensure the window message hook no longer throws. There are existing FlaUI integration tests for TitleBar behavior, so this case should be covered to prevent reintroducing the NRE.

Copilot uses AI. Check for mistakes.
continue;
}
Expand Down
Loading