U can use segues for transferring data between viewcontrollers.
check this link for more details
First of all, u need to declare your dateTimeString as a property in your .h file (ViewController.h)
Then you can call the segue using
  [self performSegueWithIdentifier:@"your_segue_identifier_name" sender:self];
Then
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:@"your_segue_identifier_name"])
    {
    }
}
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solved Sharing info between ViewControllers [duplicate]