title: Invalid Constant Value using variable as parameter
body: <pre class="lang-dart prettyprint-override"><code>var textSize = 10.0;
  // or
  double textSize = 10.0;
  </code></pre>
  
  <p>into <code>Text</code> Widget of Flutter </p>
  
  <pre class="lang-dart prettyprint-override"><code>child: const Text('Calculate Client Fees',
                     style: TextStyle(fontSize: textSize),)
  </code></pre>
  
  <p>Here it is giving error </p>
  
  <blockquote>
    <p>Invalid Constant Value</p>
  </blockquote>
  
  <p>Do we have to compulsory use <code>const</code> value? Why can not we use <code>var</code> or <code>double</code>?</p>