[Bug]: Cannot BindWithValidation on ComboBox.SelectedValue

[Nextra]

Describe the bug 🐞

The new BindWithValidation for WPF (introduced in #3874) is not able to bind to ComboBox.SelectedValue.

Instead, an Exception is thrown:

System.ArgumentException: 'Dependency property not found on Object'

Step to reproduce

1. Clone reproduction repository
2. Start the application

Reproduction repository

https://github.com/Nextra/ReactiveUIBindWithValidationBug

Expected behavior

BindWithValidation should work on ComboBox.SelectedValue

Screenshots 🖼️

No response

IDE

Visual Studio 2022

Operating system

No response

Version

No response

Device

No response

ReactiveUI Version

20.1.63

Additional information ℹ️

No response

[ChrisPulman]

Thank you for raising this, I will try to resolve this as soon as possible. List controls have always been a sticky issue for binding.

[Nextra]

Thank you.

If I might add, the BindWithValidation extension should also have nullable annotations to match the others.

[lipharDYT]

I've encountered the same error when binding:

• an ObservableCollectionExtended<T> to RadGridView.ItemSource (a control from Telerik suite),
• a bool to TextBox.IsReadOnly (I did that for testing purposes).

It'd seem binding to a DependencyProperty inherited from a parent is the actual problem:

• RadGridView.ItemSource is defined on a DataControl,
• ComboBox.SelectedValue is defined on a Selector,
• TextBox.IsReadOnly is defined on a TextBoxBase.

ValidationBindingWpf<T>.EnumerateDependencyProperties(object) uses MarkupWriter.GetMarkupObjectFor(object), which doesn't return those properties (but to be honest I got stuck trying to work out which properties it does).