如何将mapview中已经缩放的位置更改为当前设备位置

I am loading a mapview into a viewcontroller's view. When I load the mapview, it zooms directly to the location of the contact. I have button in the toolbar of my viewcontroller. When I click on this button the mapview should zoom from the already zoomed location to the current location of my iphone. This feature is similar to the one in iphone map app. How can I do this?I am loading a mapview into a viewcontroller's