在自定义Popup内容视图中，监听hardwareBack即可解决这个问题。

public class CustomPopup : PopupPage
 {
  public CustomPopup ()
  {
   //...
   this.BackgroundColor = Color.FromRgba (0, 0, 0, 0.5);
  }
  
  protected override bool OnBackgroundClicked ()
  {
   return false; // Disable background click dismiss
  }
  
  protected override bool OnBackButtonPressed ()
  {
   return false; // Disable the hardware back button
  }
  
  protected override void OnAppearing ()
  {
   base.OnAppearing ();
   
   // Listen hardware back button press
   Xamarin.Forms.Device.StartTimer (TimeSpan.FromSeconds (0.5), () =>
   {
    if (Xamarin.Forms.Device.RuntimePlatform == Device.Android && Xamarin.Forms.Application.Current.MainPage == this)
    {
     Device.StartTimer (TimeSpan.FromMilliseconds (200), () =>
     {
      base.OnBackButtonPressed(); // Manually raise back button event
      return false; // Done
     });
    }
    return false; // Done
   });
  }
  
  protected override void OnDisappearing ()
  {
   base.OnDisappearing ();
  }
 }

然后，您可以像这样实例化并显示Popup：

CustomPopup popup = new CustomPopup ();
await popup.ShowAsync ();

这样，当用户点击硬件“返回”按钮时，弹出窗口将自动关闭。