title: How to count/ find specific listview items (class)?
body: <p>I have a listView filled with Classes (PlayCard).
  I want to count the classes with the same values for <code>cardNumber</code>
  If the number is more than twice in the listView I want testBool to become true</p>
  
  <p>I got this code already:</p>
  
  <pre><code>foreach (PlayCard pCard in listView1.Items)
  {               
      if (listView1.Items.Count(i =&gt; i.cardNumber == pCard.cardNumber) &gt; 1)
      {
          pCard.testBool = true;
      }
  }
  </code></pre>
  
  <p>but i got a error:</p>
  
  <blockquote>
    <p>'Object' does not contain a definition for 'cardNumber' and no
    extension method 'cardNumber' accepting a first argument of type
    'object' could be found.</p>
  </blockquote>
  
  <pre><code>class PlayCard
  {
          public int cardNumber { get; set; }
          public int id { get; set; }
          public bool testBool = false;
  }
  </code></pre>