iPhone : How to put activity indicator on particular Tabbar click

In my app I have 5 tab bar. On particular tab bar click I want to display activity indicator for some time.

For Example,

I have 5 tab bars in which on开发者_JS百科e is Photos.

Now when user click on this Photos, It should display activity indicator for sometime and then display that Photosview.

How do I achieve this? Even I dont know How to determine which tab is selected ?

Use the tabBarController:didSelectViewController: delegate method.