Apple’s Developer documentation said that screen mirroring is available on iOS 4.3 without any magic. One should just use the mirroredScreen property, but it’s readonly.
From Apple’s developers.apple.com:
mirroredScreen
The screen being mirrored by an external display.
…If mirroring is supported and currently active, this property contains the screen object associated with the device’s main screen. This represents the screen being mirrored by the attached display. The value of this property is nil when mirroring is disabled, not supported, or no screen is connected to the device.
To disable mirroring and use the external display for presenting unique content, create a window and associate it with the corresponding screen object.
It said how to disable but not how to enable mirroring mode. How do I do it?
I want to mirror my app on the projector without creating copies of my views and update them when needed – it looks bad.
Also the simulator crashes often on using external screen emulation – is it okay?
I think currently only iPad 2 support mirroring. You can listen to notification when a external display is connected.
http://imthi.com/blog/programming/uiscreen-notifications-for-connecting-external-display-in-ios.php