Create a angular2 service and inject it in to Components by Dependency injection

In this post we are going to see how to create a service in Angular2 application and inject it in to Component by Dependency injection. For this we are going to create a sample employee service  and inject it in to two components , for this we are going to create two components Employee and Student Component, But there is a issue in this if we are injecting service in to two components individually, then the new instance are created independently for this two service, so the data wont share or change wont reflect in other component



Creating a Service:

import { Injectable } from '@angular/core';

@Injectable()
export class DataService{

private data:string[]=["Rajesh","suresh","ramu"];

getEmployees(){
    return this.data;
}

addEmployee(name){
    this.data.push(name);
}

}

Inject Service independently in Component:

   In this we are injecting service in to the components using providers in there Component decorators directly, so what will happen his it will create a new instance , because of this each and every component will use the separate instance, nothing will be shared across the components

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
    selector:'employee',
    template:`
    <div style="display:inline-block;width:400px;vertical-align:top">
        <h1>Employee </h1>
        <div>
            <input type="text" #emp />
            <button (click)="addEmployee(emp.value)" 
                    class="btn btn-sm btn-primary">Add Emp</button>
            <button (click)="getEmployee()" 
                    class="btn btn-sm btn-primary">Get Employees</button>
            <div>
                <ul class="list-group">
                    <li class="panel list-group-item-primary" 
                        *ngFor="let e of employees" style="list-style:none;">
                        {{e}}
                    </li>
                </ul>
            </div>
        </div>
    </div>
    `,
    providers:[DataService]
})
export class EmployeeComponent
{
    employees:string[];

    constructor(private dataservice:DataService){
        
    }

    addEmployee(employeeName)
    {
        this.dataservice.addEmployee(employeeName);
    }

    getEmployee(){
        this.employees = this.dataservice.getEmployees();
    }
}


@Component({
    selector:'student',
    template:`
    <div style="display:inline-block;width:400px;vertical-align:top">
        <h1>Student </h1>
        <div>
            <input type="text" #std />
            <button (click)="addStudent(std.value)" 
                    class="btn btn-sm btn-primary">Add Student</button>
            <button (click)="getStudents()" 
                     class="btn btn-sm btn-primary">Get Students</button>
            <div>
                <ul class="list-group">
                    <li class="panel list-group-item-primary" 
                        *ngFor="let s of students" style="list-style:none;">
                        {{s}}
                    </li>
                </ul>
            </div>
        </div>
        </div>
    `,
    providers:[DataService]
})
export class StudentComponent
{
    students:string[];

    constructor(private dataservice:DataService){
        
    }

    addStudent(studentName)
    {
        this.dataservice.addEmployee(studentName);
    }

    getStudents(){
        this.students = this.dataservice.getEmployees();
    }
}

Module.ts:

    import { NgModule } from '@angular/core';
    import { BrowserModule } from '@angular/platform-browser';
    import { FormsModule } from '@angular/forms';
    import { BaseRequestOptions, Http, Headers } from '@angular/http';
    import { webformComponent } from './Component/web.component'  
    import { EmployeeComponent,StudentComponent } from './employee.component'
    import { DataService } from './data.service';

    @NgModule({
        imports: [BrowserModule,FormsModule],
        exports: [],
        declarations: [webformComponent,EmployeeComponent,StudentComponent],       
        bootstrap:[webformComponent]
    })
    export class AppModule { 

    }

In module we can see the change in both the types

For ex:
In above Example we can see that the element add in the Employee doesn't reflect in Student


Output:

Inject Service Globally for all component:

  In this we are injecting service in to the module using providers in module decorator directly, so what will happen his it will create a new instance , because of this each and every component will use the same instance, everything will be shared across the components

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
    selector:'employee',
    template:`
    <div style="display:inline-block;width:400px;vertical-align:top">
        <h1>Employee </h1>
        <div>
            <input type="text" #emp />
            <button (click)="addEmployee(emp.value)" 
                    class="btn btn-sm btn-primary">Add Emp</button>
            <button (click)="getEmployee()" 
                    class="btn btn-sm btn-primary">Get Employees</button>
            <div>
                <ul class="list-group">
                    <li class="panel list-group-item-primary" 
                        *ngFor="let e of employees" style="list-style:none;">
                        {{e}}
                    </li>
                </ul>
            </div>
        </div>
    </div>
    `
})
export class EmployeeComponent
{
    employees:string[];

    constructor(private dataservice:DataService){
        
    }

    addEmployee(employeeName)
    {
        this.dataservice.addEmployee(employeeName);
    }

    getEmployee(){
        this.employees = this.dataservice.getEmployees();
    }
}


@Component({
    selector:'student',
    template:`
    <div style="display:inline-block;width:400px;vertical-align:top">
        <h1>Student </h1>
        <div>
            <input type="text" #std />
            <button (click)="addStudent(std.value)" 
                    class="btn btn-sm btn-primary">Add Student</button>
            <button (click)="getStudents()" 
                     class="btn btn-sm btn-primary">Get Students</button>
            <div>
                <ul class="list-group">
                    <li class="panel list-group-item-primary" 
                        *ngFor="let s of students" style="list-style:none;">
                        {{s}}
                    </li>
                </ul>
            </div>
        </div>
        </div>
    `
})
export class StudentComponent
{
    students:string[];

    constructor(private dataservice:DataService){
        
    }

    addStudent(studentName)
    {
        this.dataservice.addEmployee(studentName);
    }

    getStudents(){
        this.students = this.dataservice.getEmployees();
    }
}

Module.ts:

In this we can see that the Providers is injected in to module directly to use it across the components.

    import { NgModule } from '@angular/core';
    import { BrowserModule } from '@angular/platform-browser';
    import { FormsModule } from '@angular/forms';
    import { BaseRequestOptions, Http, Headers } from '@angular/http';
    import { webformComponent } from './Component/web.component'  
    import { EmployeeComponent,StudentComponent } from './employee.component'
    import { DataService } from './data.service';

    @NgModule({
        imports: [BrowserModule,FormsModule],
        exports: [],
        declarations: [webformComponent,EmployeeComponent,StudentComponent],
        providers:[DataService],
        bootstrap:[webformComponent]
    })
    export class AppModule { 

    }

For ex:
In above Example we can see that the element add in the Employee reflect in Student



Output:

 

Main Component to Bootstrap:

import { Component,ViewEncapsulation,Input,Output } from '@angular/core';


@Component({
    selector:'webform',
    template:`
    <form>    
       <student></student> 
       <employee></employee>      
    </form>`,
    styles:[`
        
    .input{        
        border: 1px solid #ddd;
        -webkit-box-shadow: inset 0 1px 2px rgba(0,0,0,.07);
        box-shadow: inset 0 1px 2px rgba(0,0,0,.07);
        background-color: #fff;
        color: #32373c;
        outline: 0;
        -webkit-transition: 50ms border-color ease-in-out;
        transition: 50ms border-color ease-in-out;
    }

    `],
    encapsulation:ViewEncapsulation.None
})
export class webformComponent{

    constructor(){

    }

}

index.html:

<body>
    <webform>Loading...</webform>
  </body>

From above post you learn how to inject the service in to the components in Angular2 applications