If it works for your use case, it will be probably be simpler to just get the inputData from those input nodes - unfortunately not all input nodes support this type - but it might work depending on your use case: Dynamo/NodeModel.cs at master · DynamoDS/Dynamo (github.com)
InputData will contain some values depending on node type.
Also - about the xaml… no idea since we can’t see your xaml, or the binding you are creating - atleast I guess thats what you’re doing - you may also need to implement INotifyPropertyChanged - read about that interface and wpf bindings.
I gave it a try to OutputData as well but after defining methods and variables I get a few errors that I don´t find a workaround;
1.- “SampleWindowViewModel.GUID” : no suitable method to override
2.- The name Properties does not exist in the current context.(I cannot find where it is defined in the link you sent above)
3.- “NotificationObject” does not contain a definition for “GUID”
I finally got it! The code I used to create the string is;
string estasi = node.OutputData.InitialValue;
Nonetheless, there are some nodes that are passing an empty value such as Revit.Selection.Categories and similar. Is there any work around to get these set values as well?