iPhone app design question

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Hi all,

I'm creating an app that first pulls some data from remote server.
When doing so I want to show the user that some action is being done and when the data is received completely from server this view disappears and the tab bar takes in.

Do you think that using tab bar as main view + modal view for the data retrieving is the way to achieve this goal?

If so, is there a way to dismiss the modal view when some model class variable changes state by KVO?

My model object changes state when whole data is received from server.
I want to use this key to dismiss the modal view and go to my tab bar view.

Thanks

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I'm asking again, is this the right way to implement this?

Thanks