Increasing a thumbs "click area" in UISlider

Question

I am creating a custom UISlider and wonder, how do you increase a thumb image's "click area" ? The code below works great, except the thumb's "click area" remains unchanged. If I am not wrong, I believe the standard thumb area is 19 px ? Lets say I would like to increase it to 35px with the following code below, what steps do I need to take? Keep in mind I am not an expert within this area at all.

EDIT The code below is corrected and ready for copy pasta! Hope it helps you!

main.h

#import "MyUISlider.h"

@interface main : MLUIViewController <UITableViewDelegate, UITableViewDataSource, UISearchBarDelegate, UIActionSheetDelegate, UIAlertViewDelegate, MFMailComposeViewControllerDelegate, UIGestureRecognizerDelegate, MLSearchTaskDelegate, MLDeactivateDelegate, MLReceiptDelegate>
{
  ..........

}

- (void)create_Custom_UISlider;

main.m

- (void)viewDidLoad
{

[self create_Custom_UISlider];
[self.view addSubview: customSlider];

}

- (void)create_Custom_UISlider
{
CGRect frame = CGRectMake(20.0, 320.0, 280, 0.0);


customSlider = [[MyUISlider alloc] initWithFrame:frame];

[customSlider addTarget:self action:@selector(sliderAction:) forControlEvents:UIControlEventValueChanged];
// in case the parent view draws with a custom color or gradient, use a transparent color

customSlider.backgroundColor = [UIColor clearColor];

UIImage *stetchLeftTrack = [[UIImage imageNamed:@"blue_slider08.png"]
           stretchableImageWithLeftCapWidth: 10.0 topCapHeight:0.0];
UIImage *stetchRightTrack = [[UIImage imageNamed:@"blue_slider08.png"]
            stretchableImageWithLeftCapWidth: 260.0 topCapHeight:0.0];


[customSlider setThumbImage: [UIImage imageNamed:@"slider_button00"] forState:UIControlStateNormal];
[customSlider setMinimumTrackImage:stetchLeftTrack forState:UIControlStateNormal];
[customSlider setMaximumTrackImage:stetchRightTrack forState:UIControlStateNormal];


                    customSlider.minimumValue = 0.0;
                    customSlider.maximumValue = 1.0;
                    customSlider.continuous = NO;
                    customSlider.value = 0.00;

}

-(void) sliderAction: (UISlider *) sender{

if(sender.value !=1.0){
 [sender setValue: 0.00 animated: YES];
}
else{
[sender setValue 0.00 animated: YES];
 // add some code here depending on what you want to do!
  }
}

EDIT (trying to subclass with the code below)

MyUISlider.h

#import <UIKit/UIKit.h>

@interface MyUISlider : UISlider {

}

@end

MyUISlider.m

#import "MyUISlider.h"

@implementation MyUISlider



- (CGRect)thumbRectForBounds:(CGRect)bounds trackRect:(CGRect)rect value:(float)value
{


return CGRectInset ([super thumbRectForBounds:bounds trackRect:rect value:value], 10 , 10);

}


@end

Answer 1

You have to override thumbRectForBounds:trackRect:value: in a custom subclass (instead of calling the method yourself like you do in your code, which does nothing except returning a value that you don't even bother to retrieve).

thumbRectForBounds:trackRect:value: is not a method to set the tumb rect, but to get it. The slider will internally call this thumbRectForBounds:trackRect:value: method to know where to draw the thumb image, so you need to override it — as explained in the documentation — to return the CGRect you want (so that it will be 35x35px as you wish).

Answer 2

Updated for Swift 3.0 and iOS 10

private func generateHandleImage(with color: UIColor) -> UIImage {
    let rect = CGRect(x: 0, y: 0, width: self.bounds.size.height + 20, height: self.bounds.size.height + 20)

    return UIGraphicsImageRenderer(size: rect.size).image { (imageContext) in
        imageContext.cgContext.setFillColor(color.cgColor)
        imageContext.cgContext.fill(rect.insetBy(dx: 10, dy: 10))
    }
}

Calling:

self.sliderView.setThumbImage(self.generateHandleImage(with: .white), for: .normal)

Original answer:

By far the easiest method is just to increase the size of the thumb image with invisible border around it:

- (UIImage *)generateHandleImageWithColor:(UIColor *)color
{
    CGRect rect = CGRectMake(0.0f, 0.0f, self.bounds.size.height + 20.f, self.bounds.size.height + 20.f);
    UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.f);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextFillRect(context, CGRectInset(rect, 10.f, 10.f));

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

And than adding this image to slider:

[self.sliderView setThumbImage:[self generateHandleImageWithColor:[UIColor redColor]] forState:UIControlStateNormal];