title: Re-open child form
body: <p>I have one Main form and two types of child form</p>
  
  <blockquote>
    <p>MainForm<br>
    ChildFormA - unique<br>
    ChildFormB - have multiple forms of this type</p>
  </blockquote>
  
  <p>I create ChildFormA with:</p>
  
  <pre><code>ChildFormA form1 = new ChildFormA();
  form1.MdiParent = this;
  form1.Show();
  </code></pre>
  
  <p>But when i close it with:</p>
  
  <pre><code>form1.Close();
  </code></pre>
  
  <p>I can't re-open it.
  I've already read some tips that I can Hide this form instead or closing it. But the X button still closes the form.
  How to re-open or how to prevent the X button to close and simple hide it?</p>