Question

I’m having trouble understanding what I’m doing wrong with the UserError class.

This is the code inside my ViewModel:

this.CheckForUpdateCmd = new ReactiveAsyncCommand(Observable.Return(true));

UserError.RegisterHandler(
    uerror =>    
    {
        logger.Error(uerror.ErrorMessage, uerror.InnerException);
        if (dlgService.ShowMessageBox(  
            this, 
            uerror.ErrorMessage, 
            ClientStrings.AboutVM_ErrorCheckUpdates, 
            MessageBoxButton.YesNo, 
            MessageBoxImage.Warning) == MessageBoxResult.Yes)
        {
            return Observable.
                Return(RecoveryOptionResult.RetryOperation);
        }
        return Observable.  
            Return(RecoveryOptionResult.FailOperation);
    });

this.
        CheckForUpdateCmd.
        ThrownExceptions.
        SelectMany(ex => 
            UserError.Throw(
                ClientStrings.AboutVM_ErrorCheckUpdates, 
                ex)).
        Subscribe(
            recoverOption =>
            {
                if (recoverOption == RecoveryOptionResult.RetryOperation)
                {
                   this.CheckForUpdateCmd.Execute(null);
                }
            });

((ReactiveAsyncCommand)this.CheckForUpdateCmd).
    RegisterAsyncAction(_ =>
        { 
            throw new Exception("TESTING 123"); 
        });

After the exception is thrown inside the async action, it is correctly propagated to my Usererror.Throw inside the SelectMany. Inside the Throw method, RxUI throws an ArgumentException with: “You must declare a backing field for this property named: recoveryOptions”

I’ve investigated this and the UserError class has a _RecoveryOptions that is being set from the UserError itself. However, I’m throwing a wrench into the whole process with this inside my App’s OnStartup event handler:

RxApp.GetFieldNameForPropertyNameFunc = prop => prop.Length == 1 ? prop.ToLower() : char.ToLower(prop[0]) + prop.Substring(1);

Basically, I want my backing fields to start with a lower-case letter, not underscore/upper. So far, RxUI has honored this until I tried to use UserError. Am I missing a step or is this a bug in RxUI?

This is for Reactive UI 3.2.0

Answer 1

This is an old bug in ReactiveUI that has been fixed long ago – either upgrade to ReactiveUI 4.x, or copy Errors.cs into your project and use that