ios - UISlider thumb to move without touching the thumb - Stack Overflow

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I have a custom UISlider inside UICollectionViewCell. I would like to be able to move the slider thumb by touching anywhere on the cell (on the purple bit). For instance, if I was to put my finger on the top right corner of the cell and slide down, I would like the thumb to slide downwards from its current position (-19.0 in this case), instead of jumping up first.

Here is my code:

@implementation CDCFaderSlider

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame: frame];
    
    if (self) {
        [self setOpaque: true];
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder: aDecoder];
    
    if (self) {
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

#pragma mark - UIControl touch event tracking

- (BOOL)beginTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    CGPoint touchPoint = [touch locationInView: self];
    
    if (CGRectContainsPoint(CGRectInset(self.thumbRect, -12.0, -12.0), touchPoint)) {
        [self positionAndUpdateValueView];
        [self fadeValueViewInAndOut: true];
    }
    return [super beginTrackingWithTouch: touch withEvent: event];
}

- (BOOL)continueTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    [self positionAndUpdateValueView];
    return [super continueTrackingWithTouch: touch withEvent: event];
}

- (void)cancelTrackingWithEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super cancelTrackingWithEvent: event];
}

- (void)endTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super endTrackingWithTouch: touch withEvent: event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super touchesEnded: touches withEvent: event];
}

- (BOOL) pointInside:(CGPoint)point withEvent:(UIEvent*)event {
    CGRect bounds = self.bounds;
    bounds = CGRectInset(bounds, 0, -70);
    return CGRectContainsPoint(bounds, point);
}

#pragma mark - Helper methods

- (void)constructSlider {
    self.valueView = [[CDCFaderValueView alloc] initWithFrame: CGRectZero];
    self.valueView.backgroundColor = UIColor.clearColor;
    self.valueView.alpha = 0.0;
    self.valueView.transform = CGAffineTransformMakeRotation((CGFloat)(M_PI * 0.5));
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self addSubview: self.valueView];
    });
}

- (void)fadeValueViewInAndOut:(BOOL)aFadeIn {
    [UIView animateWithDuration: 0.5 animations:^{
        if (aFadeIn) {
            self.valueView.alpha = 0.8;
        } else {
            self.valueView.alpha = 0.0;
        }
    } completion:^(BOOL finished){
    }];
}

- (void)positionAndUpdateValueView {
    CGRect ThumbRect = self.thumbRect;
    CGRect popupRect = CGRectOffset(ThumbRect, (CGFloat)floor(ThumbRect.size.width * 0.2), (CGFloat) - floor(ThumbRect.size.height * 0.5));
    self.valueView.frame = CGRectInset(popupRect, -30, -10);
    self.valueView.value = faderDBValues[(NSInteger)self.value];
}

#pragma mark - Property

- (CGRect)thumbRect {
    CGRect trackRect = [self trackRectForBounds: self.bounds];
    CGRect thumbR = [self thumbRectForBounds: self.bounds trackRect: trackRect value: self.value];
    
    return thumbR;
}

- (void)sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
    if (self.count > 4) {
        [super sendAction: action to: target forEvent: event];
        self.count = 0;
    } else {
        self.count++;
    }
    
    if (self.tracking == 0) {
        [super sendAction: action to: target forEvent: event];
    }
}

@end

I have a custom UISlider inside UICollectionViewCell. I would like to be able to move the slider thumb by touching anywhere on the cell (on the purple bit). For instance, if I was to put my finger on the top right corner of the cell and slide down, I would like the thumb to slide downwards from its current position (-19.0 in this case), instead of jumping up first.

Here is my code:

@implementation CDCFaderSlider

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame: frame];
    
    if (self) {
        [self setOpaque: true];
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder: aDecoder];
    
    if (self) {
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

#pragma mark - UIControl touch event tracking

- (BOOL)beginTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    CGPoint touchPoint = [touch locationInView: self];
    
    if (CGRectContainsPoint(CGRectInset(self.thumbRect, -12.0, -12.0), touchPoint)) {
        [self positionAndUpdateValueView];
        [self fadeValueViewInAndOut: true];
    }
    return [super beginTrackingWithTouch: touch withEvent: event];
}

- (BOOL)continueTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    [self positionAndUpdateValueView];
    return [super continueTrackingWithTouch: touch withEvent: event];
}

- (void)cancelTrackingWithEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super cancelTrackingWithEvent: event];
}

- (void)endTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super endTrackingWithTouch: touch withEvent: event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super touchesEnded: touches withEvent: event];
}

- (BOOL) pointInside:(CGPoint)point withEvent:(UIEvent*)event {
    CGRect bounds = self.bounds;
    bounds = CGRectInset(bounds, 0, -70);
    return CGRectContainsPoint(bounds, point);
}

#pragma mark - Helper methods

- (void)constructSlider {
    self.valueView = [[CDCFaderValueView alloc] initWithFrame: CGRectZero];
    self.valueView.backgroundColor = UIColor.clearColor;
    self.valueView.alpha = 0.0;
    self.valueView.transform = CGAffineTransformMakeRotation((CGFloat)(M_PI * 0.5));
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self addSubview: self.valueView];
    });
}

- (void)fadeValueViewInAndOut:(BOOL)aFadeIn {
    [UIView animateWithDuration: 0.5 animations:^{
        if (aFadeIn) {
            self.valueView.alpha = 0.8;
        } else {
            self.valueView.alpha = 0.0;
        }
    } completion:^(BOOL finished){
    }];
}

- (void)positionAndUpdateValueView {
    CGRect ThumbRect = self.thumbRect;
    CGRect popupRect = CGRectOffset(ThumbRect, (CGFloat)floor(ThumbRect.size.width * 0.2), (CGFloat) - floor(ThumbRect.size.height * 0.5));
    self.valueView.frame = CGRectInset(popupRect, -30, -10);
    self.valueView.value = faderDBValues[(NSInteger)self.value];
}

#pragma mark - Property

- (CGRect)thumbRect {
    CGRect trackRect = [self trackRectForBounds: self.bounds];
    CGRect thumbR = [self thumbRectForBounds: self.bounds trackRect: trackRect value: self.value];
    
    return thumbR;
}

- (void)sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
    if (self.count > 4) {
        [super sendAction: action to: target forEvent: event];
        self.count = 0;
    } else {
        self.count++;
    }
    
    if (self.tracking == 0) {
        [super sendAction: action to: target forEvent: event];
    }
}

@end

• ios
• objective-c
• uislider

Share Improve this question Follow asked Mar 12 at 16:23 NaKhNaKh 2777 bronze badges

Add a comment  | 

1 Answer 1

Sorted by: Reset to default 1

I would highly recommend writing a custom UIControl subclass, but, if you want to stick with the transformed UISlider ...

1 - we can't limit begin tracking to only a touch inside the thumb

2 - we need to track the start touch point and update the slide value based on the y-coordinate "delta" from start touch to continued touch

Here's your class, with a few changes:

CDCFaderSlider.h

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface CDCFaderSlider : UISlider

@end

NS_ASSUME_NONNULL_END

CDCFaderSlider.m - note: you didn't provide your CDCFaderValueView class, so I just implemented a simple one at the top...

#import "CDCFaderSlider.h"

@interface CDCFaderValueView : UIView
@property (assign, readwrite) float value;
@end
@implementation CDCFaderValueView
@end

@interface CDCFaderSlider ()
{
    double curVal;
    CGPoint startPT;
}
@property (strong, nonatomic) CDCFaderValueView *valueView;
@property (assign, readwrite) NSInteger count;

@end

@implementation CDCFaderSlider

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame: frame];
    
    if (self) {
        [self setOpaque: true];
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder: aDecoder];
    
    if (self) {
        [self setTransform: CGAffineTransformMakeRotation((CGFloat)(M_PI * -0.5f))];
        [self constructSlider];
    }
    return self;
}

#pragma mark - UIControl touch event tracking

- (BOOL)beginTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    // get touch point in superview
    CGPoint touchPoint = [touch locationInView: self.superview];

    // is the touch inside my frame?
    if (CGRectContainsPoint(self.frame, touchPoint)) {
        [self positionAndUpdateValueView];
        [self fadeValueViewInAndOut: true];
        // save start point
        startPT = touchPoint;
        // save current value
        curVal = self.value;
        return YES;
    }
    
    return [super beginTrackingWithTouch: touch withEvent: event];
}

- (BOOL)continueTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    // get touch point in superview
    CGPoint touchPoint = [touch locationInView: self.superview];
    
    // get the y-coordinate movement
    double yDelta = startPT.y - touchPoint.y;
    // update value to the saved value plus
    //  the yDelta as a percentage of frame height
    self.value = curVal + (yDelta / self.frame.size.height);
    
    [self positionAndUpdateValueView];
    return YES;
}

- (void)cancelTrackingWithEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super cancelTrackingWithEvent: event];
}

- (void)endTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super endTrackingWithTouch: touch withEvent: event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [self fadeValueViewInAndOut: false];
    [super touchesEnded: touches withEvent: event];
}

- (BOOL) pointInside:(CGPoint)point withEvent:(UIEvent*)event {
    CGRect bounds = self.bounds;
    bounds = CGRectInset(bounds, 0, -70);
    return CGRectContainsPoint(bounds, point);
}

#pragma mark - Helper methods

- (void)constructSlider {
    self.valueView = [[CDCFaderValueView alloc] initWithFrame: CGRectZero];
    self.valueView.backgroundColor = UIColor.cyanColor;
    self.valueView.alpha = 0.0;
    self.valueView.transform = CGAffineTransformMakeRotation((CGFloat)(M_PI * 0.5));
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self addSubview: self.valueView];
    });
}

- (void)fadeValueViewInAndOut:(BOOL)aFadeIn {
    [UIView animateWithDuration: 0.5 animations:^{
        if (aFadeIn) {
            self.valueView.alpha = 0.8;
        } else {
            self.valueView.alpha = 0.0;
        }
    } completion:^(BOOL finished){
    }];
}

- (void)positionAndUpdateValueView {
    CGRect ThumbRect = self.thumbRect;
    CGRect popupRect = CGRectOffset(ThumbRect, (CGFloat)floor(ThumbRect.size.width * 0.2), (CGFloat) - floor(ThumbRect.size.height * 0.5));
    self.valueView.frame = CGRectInset(popupRect, -30, -10);
    //self.valueView.value = faderDBValues[(NSInteger)self.value];
}

#pragma mark - Property

- (CGRect)thumbRect {
    CGRect trackRect = [self trackRectForBounds: self.bounds];
    CGRect thumbR = [self thumbRectForBounds: self.bounds trackRect: trackRect value: self.value];
    
    return thumbR;
}

- (void)sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
    if (self.count > 4) {
        [super sendAction: action to: target forEvent: event];
        self.count = 0;
    } else {
        self.count++;
    }
    
    if (self.tracking == 0) {
        [super sendAction: action to: target forEvent: event];
    }
}

@end

Example controller:

SliderTestViewController.h

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface SliderTestViewController : UIViewController

@end

NS_ASSUME_NONNULL_END

SliderTestViewController.m

#import "SliderTestViewController.h"
#import "CDCFaderSlider.h"

@interface SliderTestViewController ()
@property (strong, nonatomic) CDCFaderSlider *slider;
@property (strong, nonatomic) UIView *outlineView;
@end

@implementation SliderTestViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = UIColor.systemYellowColor;
    
    self.slider = [CDCFaderSlider new];
    self.slider.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:self.slider];
    
    UILayoutGuide *g = self.view.safeAreaLayoutGuide;
    
    [NSLayoutConstraint activateConstraints:@[
        [self.slider.widthAnchor constraintEqualToConstant:500.0],
        [self.slider.heightAnchor constraintEqualToConstant:150.0],
        [self.slider.centerXAnchor constraintEqualToAnchor:g.centerXAnchor],
        [self.slider.centerYAnchor constraintEqualToAnchor:g.centerYAnchor],
    ]];

    // because the slider get's transformed, let's add an "outline view"
    //  to show the actual frame of the slider
    self.outlineView = [UIView new];
    self.outlineView.userInteractionEnabled = NO;
    self.outlineView.layer.borderColor = UIColor.redColor.CGColor;
    self.outlineView.layer.borderWidth = 1.0;
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    
    // only execute if outlineView has not already been added
    if (!self.outlineView.superview) {
        [self.view addSubview:self.outlineView];
        self.outlineView.frame = self.slider.frame;
    }
}

@end

Looks like this when running - the red outline shows the frame of the transformed slider:

You can touch-drag anywhere in the red rectangle to move the thumb.

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