Force cocoa user control change when property changes

Question

Let's say I have a custom control called FooBox. It is just a square on the screen. It has some properties, such as color, border, etc. When I change properties, I want the FooBox to redraw itself to reflect its new properties. Is there a way to do this without writing user preferences and putting [self setNeedsDisplay: YES] in all of them?

Answer 1

Two other ways:

• Send what Accessor sends the message by sending it the message setNeedsDisplay:YES immediately after. Not always possible, and no less hassle.
• Override setValue:forKey: to add the message setNeedsDisplay: to it, and use it to set view properties. This will require boxing any numerical or structural values ​​that trade one hassle for another.

So, effectively, no.

Answer 2

I'm not sure if this is the right way to do this, but you can use NSKeyValueObserving and register the object as an observer of yourself and redraw in the -observeValueForKeyPath:ofObject:change:context: method.

Answer 3

EDIT: Peter is right in the comments, this solution only works if an observer is registered for this property. I remember that I did it on CALayer with @dynamic properties, and in this case it works the way you would like. In general, this is not a good solution to your problem.

Assuming your class meets the KVC requirements for the properties you want to trigger a re-look, I would override the -didChangeValueForKey: method to call [self setNeedsDisplay] when the key matches one of your properties. I think this is slightly better than the Peter overriding -setValue: forKey method: because it does not interfere with the normal KVC machine and does not require the box that it mentions.

 - (void)didChangeValueForKey:(NSString*)key { if ([@"propertyOne" isEqualToString:Key] || ....) { [self setNeedsDisplay]; } [super didChangeValueForKey:key]; // <- Don't forget this } 

Answer 4

I do not know about that. I will write myself some macros to do the trick, if that bothers me enough.

Answer 5

If properties are changed using NSControl, you can always set

 [theView setNeedsDisplay:YES] 

in action submitted by NSControl.