What are the Validator functions?
Built-in validator looks like –
The Following Steps involve CREATING custom validators -
There are two types of validator functions which
are the following -
1.
Async validators
2.
Sync validators
Async
validator functions that take a control instance and return an observable that
later emits a set of validation errors or null.
Sync
validator functions that take a control instance and return a set of validation
errors or null.
Angular runs only Async validators due to some
performance issues.
What Is a Template Reference variable?
A template reference
variable is a way of capturing a reference to a specific element, component,
directive, and pipe so that it can be used someplace in the same template HTML.
You should declare a
reference variable using the hash symbol (#).
The Angular
components and directives only match selectors for classes that are declared in
the Angular module.
Template
Reference Variable Syntax –
You can use a
template reference variable by two ways.
1. Using
hash symbol (#)
2. Using
reference symbol (ref-)
The
following examples of specifying a template reference variable using Input Text
Box –
I have declared a
reference variable “cellnumber” using the hash
symbol (#) and reference symbol
(ref-).
<input type="text" ref-cellnumber> //cellnumber will
be a template reference variable.
And
<input #cellnumber placeholder="Cell number"> //cellnumber will be a template
reference variable.
I have created a
reference to the input element that can be used later on in my template and the
scope for “cellnumber” variable is
the entire HTML template in which the reference is defined.
Here is how I could
use that reference to get the value of the input for instance –
//cellnumber refers to the input element
<button (click)="show(cellnumber)">click to see</button>
In the below line of
code, the variable “cellnumber” refer to the HTMLElement object instance for
the input -
show(cellnumber: HTMLInputElement){
console.log(cellnumber.value);
}
You can use the
ViewChild decorator to reference it inside your component.
import {ViewChild, ElementRef} from '@angular/core';
// Reference cellnumber variable inside Component
@ViewChild('cellnumber') cellInputRef: ElementRef;
And finally, you can
use this.nameInputRef anywhere inside your component class.
show(){
this.contactNumber = this.cellInputRef.nativeElement.value
}
Template
Reference Variable with NgForm –
Here we will discuss
about how to access NgForm directive using template reference variable.
<form (ngSubmit)="onSubmitEmployee(empForm)" #empForm="ngForm">
<label>F-Name </label><input name="f-name" required [(ngModel)]="employee.fname">
<label>L-Name </label><input name="l-name" required [(ngModel)]="employee.lname">
<label>Age
</label><input name="age" required [(ngModel)]="employee.age">
<button type="submit" [disabled]="!empForm.form.valid">Submit</button>
</form>
In the above NgForm
example contains a ngSubmit event and form directive.
The
ngSubmit – The ngSubmit directive specifies a function to
run when the form is submitted. Here on form submit onSubmitEmployee component
method will be called.
The
NgForm -
It is a nestable alias of form directive. The main purpose of ngForm is to
group the controls, but not a replacement of <form> tag.
As you know, the
HTML does not allow nesting of form elements. It is very useful to nest forms.
How
to bind to user input events to component event handlers?
Most of the DOM events are triggered by user
input and bind to these events provides a way to get inputs from a user.
The following example shows a click event binding
– [on-click.component.ts]
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-on-click',
templateUrl: './on-click.component.html',
styleUrls: ['./on-click.component.css']
})
export class OnClickComponent implements OnInit {
welcomeMsg = '';
constructor() { }
ngOnInit() { }
onClick() {
this.welcomeMsg = 'Welcome you,
Anil!';
}
}
And on-click.component.html -
<div class="msg">
<button (click)="onClick()">Click Me!</button>
<p>
{{welcomeMsg}}
</p>
</div>
OR
<!-- Canonical form, the (on-) prefix alternative -->
<div class="msg">
<button on-click="onClick($event)">Click Me!</button>
<p>
{{welcomeMsg}}
</p>
</div>
When the user clicks the button, Angular calls
the onClick method from OnClickComponent.
How to get user input from the $event object?
The DOM events carry all information that is
useful to the component.
The following example shows to get user input
from the $event – key-up.component.ts
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-key-up',
templateUrl: './key-up.component.html',
styleUrls: ['./key-up.component.css']
})
export class KeyUpComponent implements OnInit {
values = '';
constructor() { }
ngOnInit() { }
//KeyUp events.
onKeyUp(event: any) {
this.values += event.target.value + ' : ';
}
}
And key-up.component.html –
<div class="event">
<button (click)="onKeyUp($event)">KeyUp Event!</button>
<p>
{{values}}
</p>
</div>
How to get user input from a template reference variable?
This is the other way to get the user data. It is
also called #var.
“A template reference variable is mostly a
reference to a DOM element within a template. It can also be a reference to
Angular components or directives and others.”
It looks like this.
<input #name placeholder="Enter
Name">
The following example shows to get user input
from a template reference variable - template-reference.component.ts
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-template-reference',
templateUrl: './template-reference.component.html',
styleUrls: ['./template-reference.component.css']
})
export class TemplateReferenceComponent implements OnInit {
constructor() { }
ngOnInit() {
}
}
And template-reference.component.html –
<div class="event">
<button #keydownVal (keydown)="0"></button>
<p>
{{keydownVal.value}}
</p>
</div>
How to create a custom validator for both model driven and
template driven forms?
There are two types of Validators –
1. Built-in Validators
a.
Email
Validator
b.
Password
Validator
c.
Secure
Site Validator
d.
Credit
card validator
Built-in Validators -
1. Validators
.required - Requires
a form control to have a non-empty value
2. Validators
.minlength -
Requires a form control to have a value of a min length
3. Validators
.maxlength -
Requires a form control to have a value of a max length
4. Validators
.pattern -
Requires a form control’s value to match a given regex
5. And so on
Built-in validator looks like –
this.empForm = new FormGroup({
'email': new FormControl(this.employee.email,[Validators.required, ValidationService.emailValidator]),
'name': new FormControl(this.employee.name, [Validators.required,Validators.minLength(4)]), 'Dep': new FormControl(this.employee.Dep, [Validators.required, Validators.minLength(10)]), 'Desc': new FormControl(this.employee.Desc, [Validators.required, Validators.minLength(100),Validators.minLength(500)]),
});
Custom Model Form Validators – Validators are
core functions, they take as input a FormControl instance and returns either
null if it’s valid or flag for errors.
You can use the custom validator to
validate a specific requirement like -
1. Email Validator
2. Password Validator
3. Secure Site
Validator
4. Credit card
validator
5. And may more
The Following Steps involve CREATING custom validators -
Steps 1- Create validation
service using the CLI command.
ng g service validation
Steps 2 - import
validation service in your app NgModule –
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import {FormsModule, FormGroup} from '@angular/forms';
import {RouterModule} from '@angular/router';
import {HttpClientModule} from "@angular/common/http";
//MY COMPONENTS
import { AppComponent } from './app.component';
import { LoginComponent } from './login/login.component';
import { RegisterComponent } from './register/register.component';
import { EmployeeComponent } from './employee/employee.component';
//My Services
import { AuthServiceService } from './auth-service.service';
import { AuthGuard } from './auth.guard';
import { EmployeeService} from './employee.service';
import { ValidationService } from './validation.service';
@NgModule({
declarations: [
AppComponent,
LoginComponent,
RegisterComponent,
EmployeeComponent
],
imports: [
BrowserModule,
FormsModule,
HttpClientModule,
RouterModule.forRoot([
{ path: '', component: AppComponent, pathMatch: 'full' },
{ path: 'register', component: RegisterComponent },
{ path: 'employee', component: EmployeeComponent},
{ path: 'login', component: LoginComponent}])
],
providers: [EmployeeService, ValidationService],
bootstrap: [AppComponent]
})
export class AppModule { }
Steps 3 - Write the
customer validation method in your validation.service.ts -
import { Injectable } from '@angular/core';
@Injectable()
export class ValidationService {
constructor() { }
//Check Site
contains SSL Security protocol or Not.
static secureSiteValidator(control){
if (!control.value.startsWith('https') || !control.value.includes('.in')) {
return { IsSecureSite: true };
}
return null;
}
//Email Validator
static emailValidator(control) {
if (control.value.match(/[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?/)) {
return null;
}
else {
return { 'InvalidEmail': true };
}
}
//Password
Validator
static passwordValidator(control) {
if (control.value.match(/^(?=.*[0-9])[a-zA-Z0-9!@#$%^&*]{6,100}$/)) {
return null;
}
else {
return { 'InvalidPassword': true };
}
}
}
Steps 4 - Use of validation service in
your components and its looks like –
import { Component, OnInit } from '@angular/core';
import {Employee } from '../employee'
import { Validators, FormGroup, FormControl } from '@angular/forms';
import {EmployeeService} from '../employee.service'
import { ValidationService } from '../validation.service';
@Component({
selector: 'app-employee',
templateUrl: './employee.component.html',
styleUrls: ['./employee.component.css']
})
export class EmployeeComponent implements OnInit {
constructor( public _empService: EmployeeService) { }
empForm:any;
ngOnInit() {
this.empForm = new FormGroup({
'email': new FormControl(this.employee.email,[Validators.required, ValidationService.emailValidator]),
'name': new FormControl(this.employee.name, [Validators.required,Validators.minLength(4)]),
'Dep': new FormControl(this.employee.Dep, [Validators.required, Validators.minLength(10)]),
'Desc': new FormControl(this.employee.Desc, [Validators.required, Validators.minLength(100),Validators.minLength(500)]),
});
}
employee = new Employee(0,'','','','','');
submitted = false;
//Add new Employee
onSubmit() {
this.submitted = true;
let isSuccess = this._empService.addEmployee(this.employee);
if(isSuccess){
//handle success
console.log(isSuccess);
}else{
//handle errors
}
}
}
And
<div class="container">
<h1>Employee Form</h1>
<form #empForm="ngForm" (ngSubmit)="onSubmit()">
<div class="form-group">
<label for="name">Email</label>
<input type="text" class="form-control" id="email”
required [(ngModel)]="employee.email" name="email">
</div>
<div class="form-group">
<label for="name">Name</label>
<input type="text" class="form-control" id="name”
required [(ngModel)]="employee.name" name="name">
</div>
<div class="form-group">
<label for="Dep">Department</label>
<input type="text" class="form-control" id="Dep” required [(ngModel)]="employee.Dep" name="Dep">
</div>
<div class="form-group">
<label for="Desc">Desc</label>
<input type="text" class="form-control" id="Desc”
required [(ngModel)]="employee.Desc" name="Desc">
</div>
<button type="submit" class="btn
btn-success" [disabled]="!empForm.form.valid">Submit</button>
</form>
<div [hidden]="!submitted">
<h4 style="color:green;">Record Added
Successfully!</h4>
</div>
</div>
For more detail kindly refer the link - https://www.code-sample.com/2018/05/angular-6-7-documentation-and-examples.html