Sharing a variable between ViewControllers - ios

Question

I have an iPhone app with three pages, each of which allows the user to enter some text. On the final page I want to concatenate all three strings and print it out. I have a UIViewController (named PageXController) for each page and I am trying to pass variables along to the final page. The method I currently try doesn't quite work. Here is an example:
I begin by declaring a string as an instance variable in PageThreeController.h
#interface PageThreeController : UIViewController{
NSMutableString *string;
}
#property (nonatomic) NSMutableString *string;
Next I add the following to PageOneController.h,
#import "PageThreeController.h"
#interface PageOneController : UIViewController
#property (nonatomic) PageThreeController *pageThree;
In PageOneController I then attempt to set the string instance variable on page three;
- (IBAction)handleButton:(id)sender {
_pageThree = [[PageThreeController alloc] init];
_pageThree.from = [[NSMutableString alloc]init];
[_pageThree.from appendString:#"Hello World"];
NSLog(#"My string is %# on page one.", _pageThree.from);
}
The NSLog prints out My string is 'Hello World' on page one. but when I add the same NSLog on PageThreeController.m before concatenating, 'string' is NULL.
It seems that I am making a separate copy of the pageThreeViewController. What do I need to do to change the actual value of string on page three? I am really new at this

Answer 1

The easiest way to pass data between ViewControllers is using the AppDelegate, even though
there is other methods .
Method 1 - using AppDelegate.
Add the following line in your Appdelegate.
#property (strong,nonatomic) NSMutableString *str;
To access the variable from any view controller,
MyAppdeleagte appDelegate=[[UIApplication sharedApplication]delegate];
NSMutableString *Stringdata=appDelegate.str;
Method 2 -Specifying objects.
in this method , you can proceed as you are now doing and, just need to specify the
view controller instance.
let you have are navigating from one controller to another , say FirstController to Second.
Firstcontroller.h
#interface FirstController : UIViewController{
NSMutableString *string;
}
#property (nonatomic) NSMutableString *string;
SecondController.h
#interface SecondController : UIViewController{
}
#property (strong,nonatomic) FirstController *firstScreen;
Within your implementation of the FirstController, before you navigate to the SecondController ,you have to specify the instance in SecondController.
in FirstController.m
SecondController *nextScreen=[self.storyboard instantiateViewControllerWithIdentifier:#"SecondView"];
nextScreen.firstScreen=self;
Then in your SecondController.m , you can simply get the String as
_firstScreen.string;

Answer 2

Customize your prepareForSegue method in order to pass necessary vars through public properties of these controllers.
For example:
#pragma mark - PreparaForSegue
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"goToDetail"]) {
YourDestinationController *destinationController = segue.destinationViewController;
destinationController.myString = self.myStringToPass;
}
}
Where myString is a public property in YourDestinationController and myStringToPass is a property in your source controller (it could be in private scope)

Answer 3

If you need to access it from anywhere, you could store the variable in the AppDelegate. So if you had a variable like this in your AppDelegate:
#property (nonatomic) NSString *currentStringToPass;
Then you could access it from your ViewControllers by using the following code:
- (IBAction)handleButton:(id)sender {
AppDelegate *app = (AppDelegate *)[[UIApplication sharedApplication] delegate];
_pageThree = [[PageThreeController alloc] init];
_pageThree.from = [[NSMutableString alloc]init];
[app setCurrentStringToPass:#"Hello World"];
NSLog(#"My string is %# on page one.", [app currentStringToPass]);
}