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Bug: Unable to Inherit from MUX WinUI 2.x Controls in C#

See original GitHub issue

Describe the bug

Unable to create new controls inheriting from a MUX WinUI 2.x base control. The control template will never be applied.

Steps to reproduce the bug

Using the attached repro project below:

InheritTest.zip

Using the WUX namespace set a breakpoint on base.OnApplyTemplate(). When code is run the breakpoint should be hit:
Change to the MUX namespace for the base control and run again with the same breakpoint:
The breakpoint in OnApplyTemplate() is never hit and the control template is never applied.

Note that if you change the DefaultStyleKey = typeof(ColorPicker) (the base type) that will work.

Expected behavior

It should be possible to inherit from a MUX WinUI 2.x base control and have the new control template applied.

Screenshots

Using WUX the template is correctly applied:

Using MUX no template is applied:

Also see above.

Version Info

NuGet package version:

Microsoft.UI.Xaml 2.4.3

Windows app type:

UWP	Win32
Yes	N/A

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

This is a pretty major roadblock. I need a work-around or fix pretty quickly…

Issue Analytics

State:
Created 3 years ago
Reactions:1
Comments:11 (8 by maintainers)

Top GitHub Comments

2reactions

michael-hawkercommented, Jul 23, 2021

Just hit this again and forgot about DefaultStyleResourceUri.

However, when the platform can’t find the specified style for a control before OnApplyTemplate is called, it feels like this should really be throwing an exception with those types of details like “Can’t find resource X from ResourceUri Y” as then it’d be immediately obvious there’s a problem. What it’s trying to look for, and where it’s trying to look (in the example above it’d be the WinUI generic.xaml instead of the Toolkit one as we would have expected).

Otherwise, with just a silent eating it, no OnApplyTemplate and no rendering of the control, it’s just a black box and takes forever to debug. So many hours some times to realize what’s going on or to find what’s causing an issue.

1reaction

michael-hawkercommented, Jun 7, 2022

Hit this again, almost forgot about it again…

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