ReactiveUI, can execute doesn't disable button in WinForm - winforms

Question

I got a simple WinForm application with a couple of textboxes and a confirm button, I'm using ReactiveUI.
This is my ViewModel:
public CurrencyViewModel()
{
editCurrency = new Currency();
this.ValidationRule(
viewModel => viewModel.IsoCode,
isoCode => !string.IsNullOrWhiteSpace(isoCode),
"error");
this.ValidationRule(
viewModel => viewModel.Name,
name => !string.IsNullOrWhiteSpace(name),
"error");
NewCommand = ReactiveCommand.Create(() => NewItem());
SaveCommand = ReactiveCommand.Create(() => Save(), this.IsValid());
}
public string IsoCode
{
get => isoCode;
set
{
editCurrency.IsoCode = value;
this.RaiseAndSetIfChanged(ref isoCode, value);
}
}
public string Name
{
get => name;
set
{
editCurrency.Name = value;
this.RaiseAndSetIfChanged(ref name, value);
}
}
private void NewItem()
{
IsoCode = string.Empty;
Name = string.Empty;
Symbol = string.Empty;
}
I then bind my validation and my save command in the view:
this.BindValidation(ViewModel, vm => vm.IsoCode, v => v.errorLabelIsoCode.Text).DisposeWith(disposables);
this.BindValidation(ViewModel, vm => vm.Name, v => v.errorLabelName.Text).DisposeWith(disposables);
this.BindCommand(ViewModel, vm => vm.SaveCommand, v => v.sfButtonOk, nameof(sfButtonOk.Click)).DisposeWith(disposables);
this.BindCommand(ViewModel, vm => vm.NewCommand, v => v.sfButtonNew, nameof(sfButtonNew.Click)).DisposeWith(disposables);
My issue is that sfButtonOk stays enabled when i first launch the application even if isValid() is false, the command doesn't fire as intended so it's just a grapichal problem it seems. The button is disabled only if I write valid text and then cancel it.
It seems that the button is disabled only when isValid goes from true to false

Answer 1

The issue here is probably related to a view model being initialized too late, or due to the view model property not sending change notifications on the view side in time. Make sure you assign the view model to the IViewFor.ViewModel property before a call to WhenActivated, or otherwise implement INotifyPropertyChanged on the view side (also you probably don't need a WhenActivated at all because WinForms doesn't have dependency properties that might introduce a potential for a memory leak)
Additionally worth noting, that we have evergreen sample apps targeting various UI frameworks including Windows Forms in the ReactiveUI.Validation core repository https://github.com/reactiveui/ReactiveUI.Validation/blob/d5089c933e046c5ee4a13149491593045cda161a/samples/LoginApp/ViewModels/SignUpViewModel.cs#L43 Just tested the Winforms sample app, and the button availability seems to perform as we'd expect.