User control not validating
Let's take a look at the XAML code for the user control.This article is for versions of Angular 2, Angular 4 and later.
To summarize: It will be called like this when we need to validate our controls, and it will be given validators that we acquired from the hierarchical dependency injector (i.e., we got them from the usage of our component): which we can use to collect the results of any and all validators attached to our inputs, and produce a single resulting validation object containing all validation failures in one place.The first parameter in the control we leave empty as this lets you initialize your form control with a value. Angular has some built in Validators such as syntax.This would work fine but what if our form grows with more controls?This component will display actual validation failure messages inline, next to the input elements themselves. But we are going to be implementing this interface on all of our input elements, so rather than copy and paste the same code into all of our form elements, we will create an abstract base class that manages the is used to update the value of our control, but it takes an argument of type any.In fact almost all of these methods just accept arguments of type any and therefore it’s a poor interface declaration.This allows us to have zero implementation code in the actual control implementations themselves -- just templates and a constructor.
Therefore our controls will be dead simple to implement and will all share the same logic relating to model changes and validity.
This ensures that the various form-related directives will be available to our application.
Next let’s build a validation failure component, which will be shared amongst all of our form inputs and will be used when we have some validation failures.
Or what if we have multiple validators on our form controls like our email example?
The Required Field Validator is actually very simple, and yet very useful.
Angular 1 has the handy ng Messages modules to help manage error messages and validation in forms.