title: Colon after Constructor in dart
body: <p>This code is from flutter gallery and i'm trying to understanding and adapting it. I would know what this syntax means:</p>
  
  <pre><code>class DemoItem&lt;T&gt; {
    DemoItem({
      this.valueName,
      this.hintName,
      this.valueSurname,
      this.hintSurname,
      this.builder,
      this.valueToString
  
    }) : textController = new TextEditingController(text: valueToString(valueName));
  </code></pre>
  
  <p>Especially i would know <strong>what means the colon after the constructor</strong> and if there is a way to define another TextEditingController, in addition to the one already defined.</p>