Aurelia validation errors not displayed when validation initialized on attached - aurelia

Question

I want to show invalid input fields when the view is shown.
I have validation rules setup in a separate class (UserValidation) with one function (initValidatorOn).
export class UserValidation {
public _validation: Validation;
constructor(validation: Validation) {
this._validation = validation;
}
initValidatorOn(user: UserDto): ValidationGroup {
return this._validation.on(user, null)
.ensure('name').isNotEmpty();
}
}
Everything works for this setup.
export class User {
public validationGroup : ValidationGroup;
public userValidation : UserValidation;
public user : UserDto;
constructor(uv: UserValidation) {
this.userValidation = uv;
//this code works here and in activate method
this.validationGroup = this.userValidation.initValidatorOn(this.user);
}
attached() {
this.validationGroup.validate();
}
}
As I said before, the above works. But sometimes the object that I need to validate I not available in constructor or in activate function so I need to initialize validation in attached function. When I do that, my view no longer shows validation errors until I update the value in input.
So, this doesn't work
attached() {
this.validationGroup = this.userValidation.initValidatorOn(this.user);
//no validation errors displayed on the view
this.validationGroup.validate();
}
Can someone explain why errors aren't displayed on the view after I call validate when I initialize validationGroup in attached function?
Thank you.