KVO mechanism between two UIViewControllers in the UITABViewController - objective-c

Question

I am new to iPhone. I am trying to implement KVO mechanism.
What I have?
two TabController with two UIViewController, FirstViewController has a button,
SecondViewController has a UITextView
What I Want?
When button is pressed in the firstViewController, it updates member variable, which should be observed by secondViewController, and it should append to the UITextView.
What I did?
FirstViewController.h
#interface FirstViewController : UIViewController
{
IBOutlet UIButton *submitButton;
}
-(IBAction)submitButtonPressed;
#property (retain) NSString* logString;
#end
FirstViewController.m
-(IBAction)submitButtonPressed
{
NSLog (#" Submit Button PRessed ");
self.logString = #"... BUtton PRessed and passing this information ";
}
SecondViewController.h
#interface SecondViewController : UIViewController
{
IBOutlet UITextView *logView;
}
#property (nonatomic, strong) UITextView *logView;
#end
SecondViewController.m
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
......
NSArray *vControllers = [self.tabBarController viewControllers];
FirstViewController *fvc = [vControllers objectAtIndex:0];
[fvc addObserver:self forKeyPath:#"logString" options:NSKeyValueObservingOptionNew context:NULL];
return self;
}
-(void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
NSLog (#".... OBSERVE VALUE FOR KEY PATH...");
}
What output I Expect?
The String ".... OBSERVE VALUE FOR KEY PATH..." should be printed each time i press the button in the FirstViewController.
What I get?
No OUtput.
What i am doing wrong?. Kindly help me

Answer 1

put your "member variable" into a separate class file ... i.e. MODEL / view / controller. Make a singleton model object holding your data, then you can KVO that model object from any view controller.
This is roughed out pseudo-code:
#interface MyDataModel: NSObject
{
NSString *logString;
}
#property (nonatomic,retain) NSString *logString;
#end
#implementation MyDataModel
#synthesize logString;
+ (MyDataModel *) modelObject
{
static MyDataModel *instance = nil;
static dispatch_once_t once;
dispatch_once(&once, ^{
if (instance == nil)
{
instance = [[self alloc] init];
}
});
return (instance);
}
#end
in your VC1
MyDataModel *model = [MyDataModel modelObject];
[model setLogString:#"test"];
in your VC2
[model addObserver:self forKeyPath:#"logString" options:0 context:NULL];
a more sophisticated approach would use Core Data as a persistent store and to act as your data model.