ios - Updating uilabel in view controller underneath another -

i have 2 view controllers, firstviewcontroller , fourthviewcontroller. firstviewcontroller initial view controller. present fourthviewcontroller with

uiviewcontroller *fourthcontroller = [self.storyboard instantiateviewcontrollerwithid:@"fourth"]; [self presentviewcontroller:fourthcontroller animated:yes completion:nil]; 

then, in fourthviewcontroller's .m i'd change text of uilabel in firstviewcontroller. use

uiviewcontroller *firstcontroller = [self.storyboard instantiateviewcontrollerwithid:@"first"]; firstcontroller.mainlab.text = [nsmutablestring stringwithformat:@"new text"]; 

however, after use

[self dismissviewcontrolleranimated:yes completion:nil]; 

i find mainlab's text has not updated. know why?

when calling line fourthviewcontroller.m creating new instance of firstviewcontroller, rather using created one.

uiviewcontroller *firstcontroller = [self.storyboard                               instantiateviewcontrollerwithid:@"first"]; 

you can tackle in 2 ways.

1) using notification

post notification fourthviewcontroller when label text need changed.

[[nsnotificationcenter defaultcenter] postnotificationname:@"updatelabel"          object:self]; 

in firstviewcontroller viewdidload methodcreate observer waits notification fired.

[[nsnotificationcenter defaultcenter] addobserver:self         selector:@selector(updatelabelcalled:)          name:@"updatelabel"         object:nil]; 

implement updatelabelcalled: , update label.

- (void) updatelabelcalled:(nsnotification *) notification {     if ([[notification name] isequaltostring:@"updatelabel"]){         //write code update label     }  } 

2) implementing delegate

it explained here in stackoverflow. basic idea create fourthviewcontroller delegate, , create delegate method updatelabel. firstviewcontroller should implement method.