Binding pointers in Objective-C

Question

At some point in my code I set UIImageView * imageView.image to UIImage * myImage. From this point I would love to view changes of myImage in imageView.

On any myImage change, I want to imageView to show myImage. Hope you understand. Thank you.

-- Edit 1 for better explanation.

At some point in code, i set imageView's image to myClass.image. And from this point I want to imageView react on any change of myClass.image. For example myClass.image = [UIImage imageNamed:@"foo"];. Both imageView and myClass.image are properties with retain. Now, when I change the myClass.image, I also have to set imageView.image = myClass.image to see new image in image view.

Please explain properly.

priyanka
– priyanka

2012-04-04 11:37:40 +00:00
Commented Apr 4, 2012 at 11:37 — priyanka
– priyanka, Commented Apr 4, 2012 at 11:37

deanWombourne · Accepted Answer · 2012-04-04 11:55:29Z

2

Take a look at KVO.

Add an observer to the myClass.image property and when it changes, update your imageView. The code would look something like :

// To add the observer
[myClass addObserver:self forKeyPath:@"image" options:0 context:0];


// And to listen for changes
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:@"image"])
        myImageView.image = object.image;
    else
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}

answered Apr 4, 2012 at 11:55

deanWombourne

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4 Comments

user500 Over a year ago

Thank you, but I really need set imageView's image once. There is many imageViews and images in my project. I want to imageView to point to some object which can be changed... Maybe some pointer to pointer...

deanWombourne Over a year ago

You can't do what you're trying to do - UIImageView takes a pointer to a UIImage - it does't take a pointer to a pointer to a UIImage. Why do you need to set the image once - what's wrong with updating the image pointer of the imageView?

user500 Over a year ago

imageView is in cell. The cell can be dequeued (recycled) before image is re stetted.

deanWombourne Over a year ago

Then it's up to you to stop listening for changes when the cell is dequeued :)

Richard J. Ross III · Accepted Answer · 2012-04-04 11:56:48Z

1

I wrote a utility class for this a while back, and so you can download it here from my dropbox.

The syntax is like this:

[self bind:@"myImage" toObject:imageView keyPath:@"image"];
...
[self unbind:@"myImage" fromObject:imageView keyPath:@"image"];

answered Apr 4, 2012 at 11:56

Richard J. Ross III

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