title: Submit button is not working in FormGroup
body: <p>I have been trying to make a <code>FormGroup</code>, but I have a question. The submit button is not working. What would be the cause for this? <strong>create</strong> is the name of the component in my project.</p>
  
  <p><strong>create.component.html</strong></p>
  
  <p>
      <br /></p>
  
  <pre><code>&lt;form (ngSubmit)="addPost(postsForm.value)" [formGroup]="postsForm"&gt;
    &lt;p&gt;full the form&lt;/p&gt;
  
    &lt;label for="title"&gt;Title&lt;/label&gt;
    &lt;input type="text" formControlName="title" /&gt;
  
    &lt;label for="content"&gt;content&lt;/label&gt;
    &lt;textarea formControlName="content"&gt;&lt;/textarea&gt;
  
    &lt;label for="cover" class="cover"&gt;choose a file&lt;/label&gt;
    &lt;input
      type="file"
      name="cover"
      id="cover"
      (change)="handleInput(event)"
      formControlName="cover"
    /&gt;
  
    &lt;input type="submit" value="Submit" /&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p></p>
  
  <p><strong>create.component.ts</strong></p>
  
  <pre><code>import { Component, OnInit } from '@angular/core';
  import { DesignService } from '../design.service';
  import { FormGroup, FormControl, Validators } from '@angular/forms';
  
  @Component({
      selector: 'ngx-create',
      templateUrl: './create.component.html',
      styleUrls: ['./create.component.scss']
  })
  
  export class CreateComponent implements OnInit {
      constructor(private service: DesignService) {}
  
      image: any = null;
  
      public postForm = new FormGroup({
          title: new FormControl(''),
          content: new FormControl(''),
          cover: new FormControl('')
      });
  
      public handleInput($event: Event) {
          alert('handlse');
          this.image = $event.target['files'];
      }
  
      public addPost(data: FormData) {
          alert('this is add post');
          this.service.createPost(data, this.image);
      }
  
      ngOnInit() {}
  }
  </code></pre>
  
  <p>My intention is call <code>addPost()</code> function after clicking the <code>submit</code> button. Can you help me?</p>