CODEWITHSUNDEEP
iosobjective-ckey-value-observing
user4246509
user4246509

Reputation:

observeValueForKeyPath doesn't work

This my first time using KVO in an iOS project and I wanted to observe the changes of my two UILabel's after getting my position by GPS, and keep notifying me. when I run the project I got my 2 labels showing the date and they are changing by time, but observeValueForKeyPath doesn't work. 

@implementation GpsViewController{
    CLLocationManager *locationManager;
    CLLocation *crnLoc;
}

@synthesize gpsView;
@synthesize gpsModel;

- (void)viewDidLoad 
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    gpsView = [[GpsView alloc] initWithFrame:CGRectMake(0, 0, widthtScreen,heightScreen)];
    [self.view addSubview:gpsView];
    [self initLocation];
}

- (void)initLocation 
{
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    [locationManager requestWhenInUseAuthorization];
    [locationManager requestAlwaysAuthorization];
    [locationManager startUpdatingLocation];
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
    [self showAlert];
}

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
    crnLoc = [locations lastObject];
    NSLog(@"position long : %@",[NSString stringWithFormat:@"%.8f",crnLoc.coordinate.longitude]);
    NSLog(@"position lat : %@",[NSString stringWithFormat:@"%.8f",crnLoc.coordinate.latitude]);
    gpsView.longitudeLabel.text = [NSString stringWithFormat:@"%.8f",crnLoc.coordinate.longitude];
    [gpsView.longitudeLabel addObserver:self forKeyPath:@"long" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
    gpsView.latitudeLabel.text = [NSString stringWithFormat:@"%.8f",crnLoc.coordinate.latitude];
    [gpsView.latitudeLabel addObserver:self forKeyPath:@"lat" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
 }

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if([keyPath isEqualToString:@"long"]) {
        NSLog(@"observe1");
    }
    if([keyPath isEqualToString:@"lat"]) {
        NSLog(@"observe2");
    }
}

Upvotes: 1

Views: 2930

Answers (2)

zero3nna
zero3nna

Reputation: 2918

It should be more like this:

[gpsView.longitudeLabel addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

and in

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context;

your object is the corresponding label, so you could check for 

if object == gpsView.longitudeLabel

Upvotes: 2

Damian Dudycz
Damian Dudycz

Reputation: 2800

You can't just create any string inside forKeyPath. This determines the name of variable you are observing, so you can use for example "text" as forKeyPath if you want to observe changes in text.

Upvotes: 1

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