title: flutter how to check if a String contains at least one String from a list of Strings
body: <p>I want to check if the value that the user enters in a TextFormField contains at least one String in another given String.</p>
  <p>As an example, if the given String value is <code>0123456789</code> and if the user enters <code>Ab3</code> in the TextFormField, how to check if the user entered value contains at least one String in the given String?</p>
  <pre><code> String allowedChar = &quot;0123456789&quot;;
   final split = allowedChar.split('');
  </code></pre>
  <p>I tried splitting the given value like this and checked if the <code>textEditingController.text</code> contains the value for each splitted value of <code>allowedChar</code>.</p>
  <pre><code>if (_value.isNotEmpty &amp;&amp;
    textEditingController.text.contains(c)) {
      _areAlwdCharsTyped = true;
  } else if (!textEditingController.text.contains(c)) {
      _areAlwdCharsTyped = false;
  }
  </code></pre>
  <p>But <code>_areAlwdCharsTyped</code> always returns false. Could I know a way to achieve this please? Thanks in advance.</p>