title: How to convert From DateTime to unix timestamp in Flutter or Dart in general
body: <p>as you seen in the title i want to convert from DateTime to unix Timestamp in Flutter (Dart Lang).</p>
  
  <p>i saw the static Method that can convert from unix timestamp to DateTime :</p>
  
  <pre><code>DateTime.fromMillisecondsSinceEpoch(unixstamp);
  </code></pre>
  
  <p>i need the reverse </p>
  
  <pre><code>datatime =&gt; unixstamp
  </code></pre>
  
  <p>Thanks in advance.</p>