iOS development making a button to do something on other viewcontroller - ios

Question

I need to make a button to do something on another page. I know how to code a button to make wanted things on the same page(same viewcontroller) also make that button to open another page(another viewcontroller) but how can I make it both at the same time ?
Here is an example for a simple calculator.
Open the program
Enter two numbers
Click the button
SecondPage comes up and shows the result from the first page
Is it something about delegates? Please explain.
I receive some answers and thanks for that lets make it simple and make that button to write something on a label which is in the second page can you write that code too its simple a button at the first page will write something to a label on second page. First view controllers name is ru1 second viewcontrollers name is ru2
Also can you explain me where to write what I am noob and I have hard time understanding what you say ?

Answer 1

You can create a selector that does it...
[myButton addTarget:self action:#selector(mySelector) forControlEvents:UIControlEventTouchUpInside];
your selector
- (void)mySelector {
myNewViewController *secondController = [[myNewViewController alloc] init];
[secondController setMyProperty:#"SOME_VAR"];
[self.navigationController pushViewController:secondController animated:YES];
}
in the secondController.h
#property (nonatomic, strong) NSString *myProperty;
in the secondController.m
#synthesize myProperty;
in your second (ru2) controller in the -(void)viewDidLoad:
UILabel *lblSecond = [[UILabel alloc] initWithFrame:CGRect(10, 10, 20, 100)];
[lblSecond setText:myProperty];
[self.view addSubview:lblSecond];

Answer 2

In header file of second view controller add variables, that you want to pass to it:
#interface ATSecondViewController : UIViewController <UINavigationControllerDelegate>{
IBOutlet UITableView *_tableView;
NSFileManager *fileManager;
NSString *documentsDir;
IBOutlet UILabel *top_bar;
}
In method where you are pushing that new controller they will be accessible with something like this:
ATSecondViewController *detailViewController = [[ATSecondViewController alloc] initWithNibName:#"ATBuyTripViewController" bundle:nil];
detailViewController.documentsDir = #"SOME DIR";
If you synthesize that variables in SecondViewController they can be accessed through your code.

Answer 3

If the 'other' view controller exists at the time of button tap (e.g., it is somewhere in the navigation stack) you can post a notification. The 'other' view controller must do this on init:
[[NSNotificationCenter defaultCenter] addObserver:self name:YourCustomNotificationName object:nil];
And, on dealloc:
[[NSNotificationCenter defaultCenter] removeObserver:self];
On button tap (current view controller):
[[NSNotificationCenter defaultCenter] postNotificationName: YourCustomNotificationName object:self userInfo:someCustomDictionary];
'YourCustomNotificationName' is an NSString you must define somewhere visible to both view controllers.
Optionally, if you are creating the button programatically, you can use the other view controller (instead of self) when calling 'addTarget:action:forControlEvents'.
If you are using IB, I don't know... There's the whole 'file's owner' thing...