title: How do I convert a ValueNotifier into a Stream?
body: <p>I have some value notifiers on my code (<strong>TextEdittingController</strong>) and I would like to convert them into Streams, so I can use <code>rx_dart</code>'s Observable.combineLatest to check if all of them are empty at once on my code, returning the result of the check (<strong>bool</strong>) and embedding it into only one <code>StreamBuilder</code>.</p>
  
  <p>Something like that:</p>
  
  <pre><code>StreamBuilder&lt;bool&gt;(
            stream: Observe.combineLatest2(STREAM1, STREAM2, (s1,s2) =&gt; s1.text.isNotEmpty &amp;&amp; s2.text.isNotEmpty),
            builder: (BuildContext context, AsyncSnapshot&lt;bool&gt; snapshot) {
              if (snapshot.data == true) {
                return ShowUp.fifth(
                  child: Padding(
                    padding: const EdgeInsets.all(16),
                    child: RaisedButton(
                      shape: StadiumBorder(),
                      child: Text("Finish"),
                      onPressed: _finishPressed,
                    ),
                  ),
                );
              } else {
                return Container();
              }
            },
          )
  </code></pre>
  
  <p>How do I convert a ValueNotifier into a Stream?</p>