Hello Nicolas,

Kindly set the types attribute.

types : Array
List which notification kinds will be shown. Several types may be listed at same time. ‘TYPE_NOTIFICATION’ and ‘TYPE_NOTIFICATION_DIALOG’ take no effect if application is in the foreground. By default ‘[Rho.Notification.TYPE_DIALOG, Rho.Notification.TYPE_NOTIFICATION]’ is used. Example:

typeToast = [Rho.Notification.TYPE_DIALOG, Rho.Notification.TYPE_TOAST];
Possible Values :

Constant: Rho::Notification.TYPE_DIALOG (For Ruby use "::" for all "." when referencing constants)
String:dialog
Show common dialog window with buttons visible if application is active.

Constant: Rho::Notification.TYPE_NOTIFICATION (For Ruby use "::" for all "." when referencing constants)
String:notification
Show message in Android notification bar if application is at background. Touch the message opens the application.

Constant: Rho::Notification.TYPE_NOTIFICATION_DIALOG (For Ruby use "::" for all "." when referencing constants)
String:notificationDialog
This is the same as ‘TYPE_DIALOG’ + ‘TYPE_NOTIFICATION’.

Constant: Rho::Notification.TYPE_TOAST (For Ruby use "::" for all "." when referencing constants)
String:toast
Show toast window with message at foreground for a short time. The toast is visible nevertheless the application is at background or foreground but is not shown same time with any foreground pop-up.

Find the docs at Rhomobile | Notification

Code Snippet:
Rho::Notification.showPopup({
    :title =>"Displaying a pop up",
    :message => "Displaying a Normal Popup",
    :icon => "info",
    :buttons => [{:id => 'accept', :title => 'ok'}],
    :types => [Rho::Notification::TYPE_DIALOG]},url_for(:action => :popup_callback)
);

Thanks