passing null when passing nsstring - ios

Question

I am defining a NSString in a header file, but it is passing null when I try to log that string from that controller, but logs the value of the variable when if it is not called from the view controller, which is a problem because it also passes null when I try to log it into a different view controller.
I have found other similar questions, but no solutions seem to be helping, so if you have a solution that would be fantastic.
I have defined it as such in the header file:
#import <UIKit/UIKit.h>
#interface QuestionController : UIViewController
#property(weak, nonatomic) NSString *question;
#end
I have called it as such in the main file:
#import "QuestionController.h"
#implementation QuestionController
#synthesize question;
-(void) viewDidLoad{
[super viewDidLoad];
question = [NSString stringWithFormat:#"hey"];
NSLog(#"%#", question);
QuestionController *questionController = [[QuestionController alloc]init];
NSLog(#"%#", questionController.question);
}
#end

Answer 1

When you write
QuestionController *questionController = [[QuestionController alloc]init];
NSLog(#"%#", questionController.question);
you're not "logging that string from that [current] controller." Instead you've created an entirely separate instance of your QuestionController (not the same as the current view controller from which you just set question) and since you haven't set its question property at any point, that NSLog will print nil.
In your first NSLog however, i.e.
question = [NSString stringWithFormat:#"hey"];
NSLog(#"%#", question);
you are in fact logging question as set in the current instance of your QuestionController so it prints as expected.
To set questionController's question property to contain question though, try:
QuestionController *questionController = [[QuestionController alloc]init];
questionController.question = question;
NSLog(#"%#", questionController.question);

Answer 2

I have cleaned up your code to make it work and at the bottom you will find an explanation.
#import <UIKit/UIKit.h>
#interface QuestionController : UIViewController
#property(strong, nonatomic) NSString *question;
#end
#import "QuestionController.h"
#implementation QuestionController
-(void) viewDidLoad{
[super viewDidLoad];
_question = #"hey";
NSLog(#"%#", _question);
QuestionController *questionController = [[QuestionController alloc]init];
questionController.question = _question;
NSLog(#"%#", questionController.question);
}
#end
There are a few things to take note of.
NSString *question is now a strong reference, not weak. If you leave it as weak, things such as question = #"Hello" will not work because there is not strong reference to that string object and it will be deallocated.
I removed #synthesize, you no longer need to do this unless you are using a much older version of Xcode
I changed question to _question, you are now accessing the ivar directly, or you can user self.question in that instance to access it through the getter / setter.
removed the stringWithFormat part, you were not really using that method and doing just #"what you want to write" will suffice.
You are actually allocating a new version of QuestionController when you do QuestionController *questionController = [[QuestionController alloc]init]; This means that you now have a QuestionController which creates another QuestionController when it loads the view.
questionController.question = _question; sets the question string object on the new QuestionController object that you create when the view of the first QuestionController loads to the question string that you have in the original QuestionController.
Hope this helps you to understand exactly what was going on in your code. I am assuming that you are not intentionally trying to create a new QuestionController when the first one loads. This would also cause some sort of endless loop since every one you create will create another one when you access its view property.