Changes

| [[File:ui_basic_arch.png|left|600px300px]] || There are three main UI primitives:

* [http://www.blackberry.com/developers/docs/6.0.0api/net/rim/device/api/ui/Manager.html Manager]

| [[File:6bb8bb.png|left|600px]] || [http://www.blackberry.com/developers/docs/6.0.0api/index.html?net/rim/device/api/uisystem/UiApplicationApplication.html UiApplicationenterEventDispatcher] Base class for all device applications that provide a user interface.

* A UI application maintains a stack of Screen objects.As it pushes screens onto the stack, it draws them on top of any other screens already on The thread that calls this method (typically the stack.When main thread in the application pops a screen off the stack,it redraws the underlying screens as necessary.Only the screen on the top of the stack receives input events.)

* Each screen may appear only once in the display stack.The application throws a runtime exceptionif you attempt to push a single screen onto the stack more than oncebecomes theevent-dispatching thread, which will execute all drawing and event-handling code.

Note that a UI application must follow rules similarto those of traditional Swing applications: ''under normal circumstances this method does not return''.