How can I stop values being passed both ways unnecessarily? - iphone

Question

I am making a color picker. I have the following code:
View controller.h:
#interface ColorPickerViewController : UIViewController <HueSliderDelegate> {
HueSlider *hueSlider;
float hue;
}
#property (nonatomic, assign) float hue;
#end
View controller.m:
-(void)setHue:(float)hueLocal {
hue = hueLocal;
hueSlider.hue = self.hue;
}
-(void)hueChanged {
self.hue = hueSlider.hue;
}
HueSlider.h:
#protocol HueSliderDelegate <NSObject>
-(void)hueChanged;
#end
#interface HueSlider : UISlider {
HueSlider *hueSlider;
float hue;
}
#property (nonatomic, assign) float hue;
#end
HueSlider.m:
//the hue float can be set when the user moves the slider
-(void)setHue:(float)hueLocal {
hue = hueLocal;
slider.value = self.hue;
[self.delegate hueChanged];
}
The problem is that the user changes the value, the slider sends the change up to the view controller. The view controller then changes it's value for hue, which sends the change back down to the slider. Sending it back down to the slider isn't needed and if the user is moving the slider along, it'll jump back to where it was. Any advice on how I can code this differently to stop this from happening?
Note: It's not actually a slider, but I put the problem into this context because it's less complex than describing the custom control that I've made, which is similar to a slider.

Answer 1

Add an additional BOOL property to control this. Add the property to your view controller class; flip the value whenever the user begins to move the slider (could do this in touchesBegan or whatever method actually moves the slider). The property could be called anything, but the idea is:
BOOL userIsAdjustingValue;
Initialize it to NO in one of your class setup methods (init, viewDidLoad). When your user touches/begins modifying the value via the interface slider, set it to YES. You could achieve this via another delegate method, or, assuming your slider is a subview and your responder chain is intact, you could probably trigger it in the controller directly with touchesBegan and then off again with touchesEnded.
Add an if statement surrounding the call in your controller that updates the slider value. If userIsAdjusttingValue == YES, then refrain from allowing the controller to update it.
When the user is done manipulating the slider, set the value back to NO, and your controller is free to manipulate the value of the slider as it deems fit.