The new MVVM-Toolkit got some new bugs with the latest updated.

[timunie]

Describe the bug

I am not sure if it is one bug or two. For that reason I will open only one ticket by today. If you think I should divide it I will open a second issue.

Steps to Reproduce

Steps to reproduce the behavior:

Issue 1:

1. Create a new Project and use ObservableValidator in your ViewModel
2. Add two different Properties which are required. Make use of The field {0} is required and let the validator replace {0} by the DisplayName.
3. Notice that both fields get the same message

Issue 2;

1. Create a new Project and use ObservableValidator in your ViewModel
2. Do a class-level valididation
3. The user will get every issue twice.

Expected behavior

The messages should not be reused and every field should get its own message as it was in preview4. Moreover if you perform a class-level-validation every message should be displayed only one time.

Screenshots

Issue 1

• Field 1:
  

• Field 2:
  

Issue 2:

Environment

NuGet Package(s): 

Id                                  Versions                                 ProjectName                                                                                                                                                                                                                        
--                                  --------                                 -----------                                                                                                                                                                                                                        
MahApps.Metro                       {2.4.3}                                  MvvmToolkitValidationSample                                                                                                                                                                                                        
Microsoft.Toolkit.Mvvm              {7.0.0-build.848}                        MvvmToolkitValidationSample     

Package Version(s): 

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19042)
- [x] 20H2 (19042.804)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [ ] Insider Build (xxxxx)
- [X] WPF 

Device form factor:
- [X] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [X] 2019 (version: 16.8.5) 
- [ ] 2019 Preview (version: )

Additional context

The shown sample is available here: https://github.com/timunie/MvvmToolkitValidationSample

/cc @Sergio0694

Hello timunie, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌

[Sergio0694]

Hey @timunie, thanks for the report! This is interesting, I'll take a look!
Thank you for providing a sample, that helps! 👍

[Sergio0694]

Small update, I've identified and fixed the first issue. Here's the breakdown of what was causing it, for future reference.
In #3562, I've added the ability to pass an external ValidationContext to ObservableValidator, which was requested in #3729. That caused the first issue due to the fact that the ValidationContext.DisplayName property is not re-evaluated when MemberName is modified (not really sure why that is case, can't think of a reason why you'd want this). This caused ValidateProperty to pass the updated property name but with the old display name instead, which was displayed in the UI.

The fix is to just load and cache the DisplayAttribute instances in ObservableValidator and to replicate the logic to retrieve the display name that ValidationContext has, with the difference that doing this ourselves lets us reuse the same ValidationContext as requested in the other issue (and also to skip some extra allocations while we're at it).

Still investigating the other issue...

[Sergio0694]

Hey @timunie, I'm a bit confused with respect to issue 2 and need some more info to investigate this 🙂

I can repro that with Preview 4 as well, it doesn't seem to be something new in the new version.
And I'm not even sure it's actually a bug in the MVVM Toolkit per se, as things look ok from what I can see 🤔

This is the internal state of the viewmodel right after the call to ValidateAllProperties. You can see that there are (as expected) a total of 2 errors, one for each of those two properties, and yet the TextBox displays each one two times in the popup.