Dynamic forms Angular2. Conditional field visibility
<p>I would like to show a field only when there is a concrete value in other one using dynamic forms.</p>

<p>I've defined a new property "condition: boolean" for the class QuestionBase (app/question-base.ts)
My intention is to show a field dinamically when other one has a concrete value. I named this field "Conditional"</p>

<p>I think that I must include any sentence like *ngIf in the  label in app/dynamic-form-question.component.html for injecting a personalized condition, but I'm stucked. 
*ngIf doesn't evaluate question.condition when condition is defined as string. I can't find any solution to define, as a boolean, a expression in app/question.service.ts.</p>

<pre><code>e.g.
      new TextboxQuestion({
        key: 'conditional',
        label: 'Conditional Field',
        type: 'text',
        condition: brave.value == solid, (something like this, brave is other field in this form)
        order: 5
      })
</code></pre>

<p>Then a would read the condition expression for change visibility.
      </p>

<pre><code>    &lt;input *ngSwitchCase="'textbox'" [formControlName]="question.key"
            [id]="question.key" [type]="question.type"&gt;

    &lt;select [id]="question.key" *ngSwitchCase="'dropdown'" [formControlName]="question.key"&gt;
      &lt;option *ngFor="let opt of question.options" [value]="opt.key"&gt;{{opt.value}}&lt;/option&gt;
    &lt;/select&gt;

  &lt;/div&gt; 
</code></pre>

<p>Here is a <a href="http://plnkr.co/edit/xfDbICjmCGURVk6szrwp?p=preview" rel="nofollow">plunker</a>. The example is from the angular2 tutorial, with some changes.<br>
I searched a lot about dynamic forms, it's probably because I am a beginner in Angular2.  </p>

<p>Many thanks</p>