title: how to avoid open page already exist on Navigation stack?
body: <p>I am using <strong>Xamarin.forms</strong>, Some times user will click twice on same button, I am search away to avoid open same page twice, maybe disable the button after first click will work fine, but i am searching away to avoid open same page if page already exist on Navigation stack.</p>
  
  <pre><code>btnCustomerPage.Clicked += (object sender, EventArgs e) =&gt; 
  {
   //CustomerPage already Exist on Navigation Stack,So user already open it.
   Navigation.PushAsync(new CustomerPage(); 
  };
  </code></pre>