iOS Dialog Boxes
From Xojo Documentation
A Message Box displays a prompt for the user. Although it is a UI control, it does not appear on the Layout so when you drag it to your Layout, it is added to the Shelf. To learn more about Message Box go to the UserGuide:iOS Message Box topic.
A modal view is a view that is also displayed without being "pushed" onto the current view. A modal view cannot have toolbars and should not have other views pushed onto it. You can show and close a modal view using a Declare command to specific CocoaTouch APIs. To display a view modally:
// Display ModalView modally
Declare Sub presentViewController Lib "UIKit" _
Selector "presentViewController:animated:completion:" _
(parentView As Ptr, viewControllerToPresent As Ptr, animated As Boolean, completion As Ptr)
presentViewController(Self.Handle, v.Handle, True, Nil)
A button on the modal view is needed to close it:
Declare Sub dismissViewController Lib "UIKit" _
Selector "dismissViewControllerAnimated:completion:" _
(parentView As Ptr, animated As Boolean, completion As Ptr)
dismissViewController(Self.Handle, True, Nil)
Also refer to the iOSDesignExtensions open-source project which has more complete support for this.