Catel validation errors not shown in view - wpf

Question

I have a problem with Catel in showing the results of field validations (done in a view model or a model) in a view: with an error in a field, the corresponding textbox shall be marked like with a red frame. But for some reason I do not get this working.
This is a very simplified test scenario with a viewmodel having 2 integer fields, and validation rules requiring both having values < 100:
public class MainViewModel : ViewModelBase
{
public MainViewModel() : base()
{ }
protected override async Task InitializeAsync()
{
await base.InitializeAsync();
}
protected override async Task CloseAsync()
{
await base.CloseAsync();
}
public override string Title { get { return "Test"; } }
public int Value1
{
get { return GetValue<int>(Value1Property); }
set { SetValue(Value1Property, value); }
}
public static readonly PropertyData Value1Property = RegisterProperty(nameof(Value1), typeof(int), 42 );
public int Value2
{
get { return GetValue<int>(Value2Property); }
set { SetValue(Value2Property, value); }
}
public static readonly PropertyData Value2Property = RegisterProperty(nameof(Value2), typeof(int), 99);
protected override void ValidateFields(List<IFieldValidationResult> validationResults)
{
if (Value1 >= 100)
{
validationResults.Add(FieldValidationResult.CreateError(Value1Property, "Value1 must be < 100" ));
}
if (Value2 >= 100)
{
validationResults.Add(FieldValidationResult.CreateError(Value1Property, "Value2 must be < 100"));
}
}
protected override void ValidateBusinessRules(List<IBusinessRuleValidationResult> validationResults)
{ }
}
}
Please note: in my real project, the fields and validation would be in a model, but for test reasons I have stripped this down to just a view and a view model.
And this simple view has the viewmodel as the datacontext:
<catel:Window x:Class="WPF_Catel_Validation.Views.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:catel="http://schemas.catelproject.com">
<StackPanel Orientation="Vertical" HorizontalAlignment="Left">
<TextBox Text="{Binding Value1, NotifyOnValidationError=True, ValidatesOnDataErrors=True}" Width="100" />
<TextBox Text="{Binding Value2, NotifyOnValidationError=True, ValidatesOnDataErrors=True}" Width="100" />
</StackPanel>
</catel:Window>
The connection between view and viewmodel works. The view also shows an error when a non-numeric text is entered in a textbox. The viewmodel with the method ValidateFields() also identifies any errors, but the view does not show these validation errors with a red frame around the textbox.
I have done my tests with Catel 5.8.0 and .NET 4.7.2. I wonder a little how the Catel-class ViewModelBase can implement INotifyDataErrorInfo, but the event ErrorsChanged is not visible in that class. But in general I have no clue if something is wrong with my viewmodel, or my view, or with Catel, or anything else? I also did not find any up-to-date documentation on Catel. Any suggestions are highly appreciated - thanks!

Answer 1

Probably you need to set DeferValidationUntilFirstSave to false if you want to show them immediately.