KVO Setting value to label

[Sander]

Hi all,

After a lot of trying I got this working code:
It works fine.

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    NextViewController *nvc = segue.destinationViewController;
    
    
    [nvc addObserver:self forKeyPath:@"textFieldA.text" options:(NSKeyValueObservingOptionNew) context:nil];
    
    
    [nvc addObserver:self forKeyPath:@"textFieldB.text" options:(NSKeyValueObservingOptionNew) context:nil];
    
    [nvc addObserver:self forKeyPath:@"removeKeyValueObserver" options:(NSKeyValueObservingOptionNew) context:nil];
}


-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"object %@", object);
    NSLog(@"keyPath %@", keyPath);
    NSLog(@"change %@", change);
    

    
    if ([keyPath isEqualToString:@"removeKeyValueObserver"] && [[change objectForKey:@"new"] boolValue])
    
    {
        [object removeObserver:self forKeyPath:@"textFieldA.text"];
        [object removeObserver:self forKeyPath:@"textFieldB.text"];
        [object removeObserver:self forKeyPath:@"removeKeyValueObserver"];

    }
          
}

Now my question is, how do I set the text of lbl1 with the value of textFieldA?

lbl1 is on my view.

Kind Regards

[Duncan C]

Originally Posted by Sander

Hi all,

After a lot of trying I got this working code:
It works fine.

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    NextViewController *nvc = segue.destinationViewController;
    
    
    [nvc addObserver:self forKeyPath:@"textFieldA.text" options:(NSKeyValueObservingOptionNew) context:nil];
    
    
    [nvc addObserver:self forKeyPath:@"textFieldB.text" options:(NSKeyValueObservingOptionNew) context:nil];
    
    [nvc addObserver:self forKeyPath:@"removeKeyValueObserver" options:(NSKeyValueObservingOptionNew) context:nil];
}


-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"object %@", object);
    NSLog(@"keyPath %@", keyPath);
    NSLog(@"change %@", change);
    

    
    if ([keyPath isEqualToString:@"removeKeyValueObserver"] && [[change objectForKey:@"new"] boolValue])
    
    {
        [object removeObserver:self forKeyPath:@"textFieldA.text"];
        [object removeObserver:self forKeyPath:@"textFieldB.text"];
        [object removeObserver:self forKeyPath:@"removeKeyValueObserver"];

    }
          
}

Now my question is, how do I set the text of lbl1 with the value of textFieldA?

lbl1 is on my view.

Kind Regards

What you're doing is a bad idea. A view controller's view hierarchy should be treaded as private. Rather than observing the labels' text value, set up string properties in the other view controller that get installed in the label field. Then observe those properties rather the labels themselves.

I don't usually try to decode the dictionary of info that comes in from a KVO notification. Instead, I just use an if statement to figure out which key changed, and then get the new value of the property directly. it's simpler.

[Sander]

Ok,

So if I understand you right, then I have to set my label fields to strings in the other view and then read the strings with KVO?

[Duncan C]

Originally Posted by Sander

Ok,

So if I understand you right, then I have to set my label fields to strings in the other view and then read the strings with KVO?

Yes.

Only a view controller should read or write data to its views. A view controller's public interface should provide a way to set values that get displayed to that view controller's on-screen interface. Properties are a really easy way to transfer string settings for labels into a view controller.

Just add a line in your view controller's viewWillAppear method that copies the string value from the property into the label's text property:

-(void) viewWillAppear: (BOOL) animated;
{
  myLabel.text = self.propertyString;
}

If you want to, you can have a view controller be a KVO observer of a property string, and pick up changes automatically.