title: Ng-admin: How to show different fields according to user's selection?
body: <p>I am using ng-admin to write a admin management. I met below issue, can somebody help me?</p>
  
  <p>In my creationView, I would like to show different fields(text/video/pictures) according to the selection of "type" field. How I can make it? </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var articles = nga.entity('articles');
  articles.creationView().fields([
        nga.field('type','choice')
              .validation({ required: true })
              .choices([
                  // 1: txt, 2: pic, 3: vid
                  { value: 1, label: 'Text'},
                  { value: 2, label: 'Picture'},
                  { value: 3, label: 'Video'},
              ]),
        nga.field('txt','file')
            .attributes({ placeholder: 'Write something... !' }),
        nga.field('pic','file')
            .label('Picture(.jpg|.png)')
            .uploadInformation({ 'url': '/api/adminapi/uploadPicture', 'apifilename': 'pictures', 'accept': 'image/jpg,image/png'}),
        nga.field('vid','file')
           .label('Video(.mp4)')
           .uploadInformation({ 'url': '/api/adminapi/uploadVideo', 'apifilename': 'video', 'accept': 'video/mp4'}),
  
  ])</code></pre>
  </div>
  </div>
  </p>