Question

I came across Set a ValidationError by Code, by Christian Mosers

ValidationError validationError = new ValidationError(regexValidationRule, 
    textBox.GetBindingExpression(TextBox.TextProperty));

validationError.ErrorContent = "This is not a valid e-mail address";

Validation.MarkInvalid(textBox.GetBindingExpression(TextBox.TextProperty), 
    validationError);

How can I use this in my ViewModel?

Answer 1

There are other ways to get errors out of the VM, for example by implementing IDataErrorInfo or by throwing exceptions in setters (the binding then needs to validate on exception).