PushAsync is not supported globally on iOS, please use a NavigationPage.

I created a Xamarin.Forms Shared project referencing to the MobileCRM from the samples site
and when i tried to navigate to another page in iOS
it show me this error:

"System.InvalidOperationException: PushAsync is not supported globally on iOS, please use a NavigationPage."

and here is my code snippet:

Button button2 = new Button
{
Text = " Go to Image Demo Page ",
Font = Font.SystemFontOfSize(NamedSize.Large),
BorderWidth = 1
};
button2.Clicked += async (sender, args) =>
await Navigation.PushAsync(new ImageDemoPage());