iOS：在视图控制器之间传递数据

Question

I'm using Facebook API, and when the user select a place (CheckIn), I want to open another view and pass this place (FBGraphPlace), but in the "SecondViewController" the variable is null when the method "viewDidLoad" is executed. When the user select the place:

if (secondViewController == nil)
{
    SecondViewcontroller *secondViewcontroller =
    [[SecondViewcontroller alloc]
     initWithNibName:NSStringFromClass([SecondViewcontroller class])
     bundle:[NSBundle mainBundle]];

    self.secondViewcontroller = secondViewcontroller;
}

// How you reference your navigation controller will
// probably be a little different
UIBarButtonItem *newBackButton = [[UIBarButtonItem alloc] initWithTitle: @"Back" style: UIBarButtonItemStyleBordered target: nil action: nil];

[[self navigationItem] setBackBarButtonItem: newBackButton];

secondViewController.place = self.selectedPlace;

[self.navigationController
 pushViewController:self.secondViewcontroller
 animated:YES];

Answer 1

您应该先执行pushViewController，然后分配place变量