iPhone: on button click Tab does not change

Hi I am not able to change Tab on button click so what could be the problem? Here is the code. I have connected all outlets properly.

 -(IBAction) BackPressed :(id) sender  
{

 Calculator *calculator1 = [[Calculator alloc] initWithNibName:@"Calculator" bundle:nil];

 [self.tabBarController setSelectedIndex:2];

 [self.tabBarController setSelectedViewController:calculat开发者_开发百科or1];}

please Help and Suggest

Note that you're creating a new Calculator instance on your button click handler. What you probably want to do is change the tab on an existing view controller, and not to create a new one.

you have to set viewcontrollers to tabbarcontroller initially.for example

   self.tabBarController.viewControllers = [NSArray arrayWithObjects:navFirst,navsecond, navthird, navfourth, navfifth,nil]; 

after that you can do the selectedIndex operation.please check the questions and answer in the link.