Introduction:
Angular is a popular framework used in developing web applications. It comes equipped with useful features such as form validation to ensure that user input is correct before it is sent to the server. However, there are instances when we may need to add validators dynamically instead of hardcoding them in the template.
In this article, we will learn how to add validators dynamically using the SetValidators function in Angular.
I. What is SetValidators?
The SetValidators function is a method used in Angular to add validators dynamically to a form control. It is part of the Form Control API which provides access to the state and validation of an individual form control.
The SetValidators function is called on a form control instance and takes an array of validator functions as its argument. It can be used to add or update validators dynamically at runtime.
II. Adding validators dynamically using SetValidators
1. Create a form group instance
The first step in adding validators dynamically using SetValidators is to create a form group instance. A form group is a collection of form controls that are linked to the same underlying data model. It is used to represent a form in Angular.
To create a form group, we use the FormBuilder service provided by Angular. The FormBuilder service provides convenient methods for creating form controls, form groups, and form arrays.
Here is an example of how to create a form group using the FormBuilder service:
“`
import { Component } from ‘@angular/core’;
import { FormBuilder, FormGroup, Validators } from ‘@angular/forms’;
@Component({
…
})
export class MyComponent {
myForm: FormGroup;
constructor(private fb: FormBuilder) {
this.myForm = this.fb.group({
name: [”, Validators.required],
email: [”, Validators.email]
});
}
}
“`
In the code above, we import the FormBuilder, FormGroup and Validators classes from the Angular forms module. We then inject the FormBuilder service into our component constructor.
We create a form group called myForm, which has two form controls – name and email. The name control is required while the email control requires a valid email address.
2. Add validation dynamically
To add validators dynamically, we use the SetValidators function. We call this function on a form control instance and pass in an array of validator functions as its argument.
Here is an example of adding validators dynamically to the email control in the myForm form group:
“`
import { Component } from ‘@angular/core’;
import { FormBuilder, FormGroup, Validators } from ‘@angular/forms’;
import { FormControl } from ‘@angular/forms’;
@Component({
…
})
export class MyComponent {
myForm: FormGroup;
emailControl: FormControl;
constructor(private fb: FormBuilder) {
this.myForm = this.fb.group({
name: [”, Validators.required],
email: [”, Validators.email]
});
// Get a reference to the email control
this.emailControl = this.myForm.get(’email’) as FormControl;
// Dynamically add a validator to the email control
this.emailControl.setValidators(Validators.minLength(10));
this.emailControl.updateValueAndValidity();
}
}
“`
In the code above, we first get a reference to the email control using the get method of the form group.
We then call the SetValidators function on the email control and pass in the Validators.minLength(10) function as its argument. The updateValueAndValidity function is called to update the email control’s value and validation status.
Now, the email control requires a minimum length of 10 characters in addition to the email validation.
III. FAQs
1. What are validators in Angular?
Validators in Angular are functions used to validate user input in forms. They ensure that the user input meets certain requirements before it is submitted to the server. Angular provides a set of built-in validators such as required, min, max, email, and pattern. Custom validators can also be created by developers.
2. Why do we need to add validators dynamically?
There are instances when we need to add validators dynamically instead of hardcoding them in the template. For example, we may want to add different validators based on user input or based on some other condition.
3. What other methods can be used to add validators dynamically?
Aside from the SetValidators function, we can also use the clearValidators function to remove validators dynamically. We can also use the setAsyncValidators function to add asynchronous validators.
4. Can we update validators dynamically after they have been added?
Yes, we can update validators dynamically by calling the SetValidators function again with a new array of validator functions. We can also use the clearValidators function to remove validators before adding new ones.
Conclusion:
In this article, we have learned how to add validators dynamically using the SetValidators function in Angular. We have seen how to create a form group using the FormBuilder service and how to add validators dynamically to a form control.
By using SetValidators, we can add validators dynamically based on user input or any other condition, giving us more control over form validation in our Angular applications.