Disable specific settings dynamically

I am developing an iPhone app which uses Settings.bundle to let the user choose some options.

I have two questions regarding this:

1. How can I completely remove/hide some setting? (for instance if the app is running on iPhone 3G I want to hide settings regarding t开发者_如何学Che compass)
2. How can I disable (fade) a setting? (for instance, I have two Toggle Switches and if the first is set to OFF the second one has no meaning and should be disabled)

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You can't. Your app cannot dynamically influence what is shown in the Settings app.