title: Angular Material | Check if dialog is open
body: <p>I'm using the <a href="https://material.angular.io/components/dialog/overview" rel="noreferrer">Angular Material dialog</a> to show a warning message in my app. </p>
  
  <p>I need to check if a dialog is already open like this:</p>
  
  <pre><code>private _openDialog() {
    // if (this.dialog.isOpen()) return; &lt;-- NOT WORKING
    this.dialog.open(WarningComponent, {
      width: '450px',
      height: '380px',
    });
  </code></pre>
  
  <p>}</p>
  
  <p><strong>Question:</strong> Is there any way to check if a Angular Material Dialog box is already open?</p>