How to refresh bindings for sub-variables?

[LouisIngenthron]

Given the following structures:

class FooA
{
    public String Bar { get; set; }

    public override String ToString()
    {
        return Bar;
    }
}

class FooB
{
    public FooA Foo { get; set; }
}

partial class MyViewModel : ViewModelBase
{
    [ObservableProperty]
    public FooB _Data;
}

And the following XAML snippet:

<TextBlock Text="{Binding Data.Foo}"/>

I can only get the binding to refresh automatically when I change DataContext.Data specifically.
When I change the DataContext itself, nothing happens.
When I change DataContext.Data.Foo, nothing happens.
When I change DataContext.Data.Foo.Bar, nothing happens.

Now, I sort of get why that is (I'm only observing the Data property), but even when I manually call OnPropertyChanged for Data.Foo, nothing happens still. And I can't find any way to manually refresh. And, as mentioned above, I even tried the nuclear option of giving it a whole brand new MyViewModel DataContext instance, and that didn't refresh the value. I confirmed by stepping through the code... the values had changed, but the UI stubbornly refused to follow.

So, how do I tell my UI that these sub-values changed and it needs to refresh?

[IanRawley]

FooA and FooB need to implement INotifyPropertyChanged and raise change notifications if you want changes on them to trigger UI updates. You can't have MyViewModel raise a manual change for "Data.Foo" because that's not a property that exists. The binding system watches MyViewModel for changes to "Data" and FooB for changes to "Foo". FooB will never raise changes of Foo, and Data isn't changing so the binding systems do nothing.

This is a bit different from the UWP / WPF because they automatically generators wrappers for properties of classes that didn't implement INPC for you. In Avalonia you have to do it yourself.

As for not registering changes to DataContext, you'd need to provide a more complete sample to see what's causing that.

[LouisIngenthron]

The data classes I'm using come from a third-party DLL, and wrapping all of them manually sounds nightmarish and bloaty and difficult to maintain.

Is there a way to just tell the UI to "refresh all bound values"? Do a full invalidate all?

[msneijders]

For that you would need to assign a new instance (or at least another instance) of FooB to MyViewModel.Data (only triggering a propertychangedevent on 'Data' is not enough, internally it checks for object instance). The FooA instance can stay the same one probably (but you must get it over to your new FooB instance).

[thevortexcloud]

Is there a way to just tell the UI to "refresh all bound values"? Do a full invalidate all?

It's not really bound if you need to do that. But yes you can by calling one of the update methods on a control and using an explicit binding. There is some information here:

#14965

It is however very verbose.

Anyway, wrapping is the most logical (and in my opinion, correct) choice. View models should wrap models. Your third party code is your model.