How to get the center of the thumb image of UISlider

Question

I'm creating a custom UISlider to test out some interface ideas. Mostly based around making the thumb image larger.

I found out how to do that, like so:

UIImage *thumb = [UIImage imageNamed:@"newThumbImage_64px.png"];   [self.slider setThumbImage:thumb forState:UIControlStateNormal];   [self.slider setThumbImage:thumb forState:UIControlStateHighlighted];   [thumb release];   

To calculate a related value I need to know where the center point of the thumb image falls when it's being manipulated. And the point should be in it's superview's coordinates.

Looking at the UISlider docs, I didn't see any property that tracked this.

Is there some easy way to calculate this or can it be derived from some existing value(s)?

Answer 1

This will return the correct X position of center of thumb image of UISlider in view coordinates:

- (float)xPositionFromSliderValue:(UISlider *)aSlider {      float sliderRange = aSlider.frame.size.width - aSlider.currentThumbImage.size.width;      float sliderOrigin = aSlider.frame.origin.x + (aSlider.currentThumbImage.size.width / 2.0);       float sliderValueToPixels = (((aSlider.value - aSlider.minimumValue)/(aSlider.maximumValue - aSlider.minimumValue)) * sliderRange) + sliderOrigin;       return sliderValueToPixels; } 

Put it in your view controller and use it like this: (assumes property named slider)

float x = [self xPositionFromSliderValue:self.slider]; 

Answer 2

I tried this after reading the above suggestion -

yourLabel = [[UILabel alloc]initWithFrame:....];  //Call this method on Slider value change event  -(void)sliderValueChanged{     CGRect trackRect = [self.slider trackRectForBounds:self.slider.bounds];     CGRect thumbRect = [self.slider thumbRectForBounds:self.slider.bounds                                trackRect:trackRect                                    value:self.slider.value];      yourLabel.center = CGPointMake(thumbRect.origin.x + self.slider.frame.origin.x,  self.slider.frame.origin.y - 20); } 

For Swift version

func sliderValueChanged() -> Void {         let trackRect =  self.slider.trackRect(forBounds: self.slider.bounds)         let thumbRect = self.slider.thumbRect(forBounds: self.slider.bounds, trackRect: trackRect, value: self.slider.value)         yourLabel.center = CGPoint(x: thumbRect.origin.x + self.slider.frame.origin.x + 30, y: self.slider.frame.origin.y - 60)     } 

I could get most accurate value by using this snippet.