How to get the center of the thumb image of UISlider

willc2_23973 0
Viewed 28872

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)?

uislider user-interface iphone cocoa-touch
12 Answers

It's better to use -[UIView convertRect:fromView:] method instead. It's cleaner and easier without any complicated calculations:

- (IBAction)scrub:(UISlider *)sender
{
    CGRect _thumbRect = [sender thumbRectForBounds:sender.bounds
                                        trackRect:[sender trackRectForBounds:sender.bounds]
                                            value:sender.value];
    CGRect thumbRect = [self.view convertRect:_thumbRect fromView:sender];

    // Use the rect to display a popover (pre iOS 8 code)
    [self.popover dismissPopoverAnimated:NO];
    self.popover = [[UIPopoverController alloc] initWithContentViewController:[UIViewController new]];
    [self.popover presentPopoverFromRect:thumbRect inView:self.view
                permittedArrowDirections:UIPopoverArrowDirectionDown|UIPopoverArrowDirectionUp animated:YES];
}
user_12206420

I approached it by first mapping the UISlider's value interval in percents and then taking the same percent of the slider's size minus the percent of the thumb's size, a value to which I added half of the thumb's size to obtain its center.

    - (float)mapValueInIntervalInPercents: (float)value min: (float)minimum max: (float)maximum
    {
        return (100 / (maximum - minimum)) * value -
               (100 * minimum)/(maximum - minimum);
    }    


    - (float)xPositionFromSliderValue:(UISlider *)aSlider
    {
        float percent = [self mapValueInIntervalInPercents: aSlider.value
                              min: aSlider.minimumValue
                              max: aSlider.maximumValue] / 100.0;

        return percent * aSlider.frame.size.width -
               percent * aSlider.currentThumbImage.size.width +
               aSlider.currentThumbImage.size.width / 2;
    }
user_1471410

step 1 :get View for detect position (use same extension top commet of# Ovi Bortas)

@IBOutlet weak var sliderView: UIView!

step 2 : set label frame for add sub view func setLabelThumb(slider:UISlider,value:Float){ slider.value = value

let label = UILabel(frame:  CGRect(x: slider.thumbCenterX - 20, y: slider.frame.origin.y - 25, width: 50, height: 30))
label.font = UIFont.systemFont(ofSize: 10.0)
label.textColor = UIColor.red
label.textAlignment = .center
label.text = "\(value) kg."

sliderView.addSubview(label)

}

user_99546050
Related