iOS - Resize vertical views with separator view

This question is similar to the question I asked here. Rob answered me and his code worked perfectly. I am trying to do the same thing but make the views vertical.

Here is what I have now.

I my viewDidLoad:

UIView *previousContentView = nil;

    for (NSInteger i = 0; i < 4; i++) {
        UIView *contentView = [self addRandomColoredView];
        [self.view.leadingAnchor constraintEqualToAnchor:contentView.leadingAnchor].active = true;
        [self.view.trailingAnchor constraintEqualToAnchor:contentView.trailingAnchor].active = true;
        if (previousContentView) {
            VerticalSeparatorView *view = [[VerticalSeparatorView alloc] init];
            [view addSeparatorBetweenView:previousContentView secondView:contentView];
            NSLayoutConstraint *width = [contentView.widthAnchor constraintEqualToAnchor:previousContentView.widthAnchor];
            width.priority = 250;
            width.active = true;
        } else {
            [self.view.leftAnchor constraintEqualToAnchor:contentView.leftAnchor].active = true;
        }
        previousContentView = contentView;
    }
    [self.view.rightAnchor constraintEqualToAnchor:previousContentView.rightAnchor].active = true;

In my VerticalSeparatorView:

@implementation VerticalSeparatorView

#pragma mark - Configuration

/** Add a separator between views

 This creates the separator view; adds it to the view hierarchy; adds the constraint for height;
 adds the constraints for leading/trailing with respect to its superview; and adds the constraints
 the relation to the views above and below

 @param firstView  The UIView above the separator
 @param secondView The UIView below the separator
 @returns          The separator UIView
 */

- (instancetype)addSeparatorBetweenView:(UIView *)firstView secondView:(UIView *)secondView {
    VerticalSeparatorView *separator = [[VerticalSeparatorView alloc] init];
    [firstView.superview addSubview:separator];
    separator.firstView = firstView;
    separator.secondView = secondView;

    [NSLayoutConstraint activateConstraints:@[
                                              [separator.widthAnchor constraintEqualToConstant:kTotalWidth],
                                              [separator.superview.leadingAnchor constraintEqualToAnchor:separator.leadingAnchor],
                                              [separator.superview.trailingAnchor constraintEqualToAnchor:separator.trailingAnchor],
                                              [firstView.rightAnchor constraintEqualToAnchor:separator.leftAnchor constant:kMargin],
                                              [secondView.leftAnchor constraintEqualToAnchor:separator.rightAnchor constant:-kMargin],
                                              ]];

    separator.leftConstraint = [separator.leftAnchor constraintEqualToAnchor:separator.superview.leftAnchor constant:0]; // it doesn't matter what the constant is, because it hasn't been enabled

    return separator;
}

- (instancetype)init {
    self = [super init];
    if (self) {
        self.translatesAutoresizingMaskIntoConstraints = false;
        self.userInteractionEnabled = true;
        self.backgroundColor = [UIColor redColor];
    }
    return self;
}

#pragma mark - Handle Touches

// When it first receives touches, save (a) where the view currently is; and (b) where the touch started

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    self.oldX = self.frame.origin.x;
    self.firstTouch = [[touches anyObject] locationInView:self.superview];
    self.leftConstraint.constant = self.oldX;
    self.leftConstraint.active = true;
}

// When user drags finger, figure out what the new top constraint should be

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];

    // for more responsive UX, use predicted touches, if possible

    if ([UIEvent instancesRespondToSelector:@selector(predictedTouchesForTouch:)]) {
        UITouch *predictedTouch = [[event predictedTouchesForTouch:touch] lastObject];
        if (predictedTouch) {
            [self updateTopConstraintOnBasisOfTouch:predictedTouch];
            return;
        }
    }

    // if no predicted touch found, just use the touch provided

    [self updateTopConstraintOnBasisOfTouch:touch];
}

// When touches are done, reset constraint on the basis of the final touch,
// (backing out any adjustment previously done with predicted touches, if any).

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    [self updateTopConstraintOnBasisOfTouch:[touches anyObject]];
}

/** Update top constraint of the separator view on the basis of a touch.

 This updates the top constraint of the horizontal separator (which moves the visible separator).
 Please note that this uses properties populated in touchesBegan, notably the `oldY` (where the
 separator was before the touches began) and `firstTouch` (where these touches began).

 @param touch    The touch that dictates to where the separator should be moved.
 */
- (void)updateTopConstraintOnBasisOfTouch:(UITouch *)touch {
    // calculate where separator should be moved to

    CGFloat x = self.oldX + [touch locationInView:self.superview].y - self.firstTouch.y;

    // make sure the views above and below are not too small

    x = MAX(x, self.firstView.frame.origin.x + kMinWidth - kMargin);
    x = MIN(x, self.secondView.frame.origin.x + self.secondView.frame.size.width - (kMargin + kMinWidth));

    // set constraint

    self.leftConstraint.constant = x;
}

#pragma mark - Drawing

- (void)drawRect:(CGRect)rect
{
    CGRect separatorRect = CGRectMake(kMargin, 0, kVisibleWidth, self.bounds.size.height);
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:separatorRect];
    [[UIColor blackColor] set];
    [path stroke];
    [path fill];
}

@end

I am connecting the contentView right anchor to the separator left anchor and contentView left anchor to the separator right anchor but nothing is displayed after I run this code. What am I doing wrong?

A couple of observations:

The constraints in the for loop, which was written for a horizontal separator, are all backwards when dealing with vertical separator. You have to replace all occurrences of top/bottom anchors with leading/trailing, and vice versa. You've done this (largely) within the VerticalSeparatorClass, not not where you are creating your content views.

UIView *previousContentView = nil;

for (NSInteger i = 0; i < 4; i++) {
    UIView *contentView = [self addRandomColoredView];
    [self.view.topAnchor constraintEqualToAnchor:contentView.topAnchor].active = true;
    [self.view.bottomAnchor constraintEqualToAnchor:contentView.bottomAnchor].active = true;
    if (previousContentView) {
        [VerticalSeparatorView addSeparatorBetweenView:previousContentView secondView:contentView];
        NSLayoutConstraint *width = [contentView.widthAnchor constraintEqualToAnchor:previousContentView.widthAnchor];
        width.priority = 250;
        width.active = true;
    } else {
        [self.view.leadingAnchor constraintEqualToAnchor:contentView.leadingAnchor].active = true;
    }
    previousContentView = contentView;
}
[self.view.trailingAnchor constraintEqualToAnchor:previousContentView.trailingAnchor].active = true;

Also, I'm unclear why you made addSeparatorBetweenView an instance method rather than a class method like it was before, because now you're dealing with two separate instances. It's not a problem, but it's inefficient.

Also, I think a few constraints that should have been flipped between top/bottom and leading/trailing slipped through. You want:

+ (instancetype)addSeparatorBetweenView:(UIView *)firstView secondView:(UIView *)secondView {
    VerticalSeparatorView *separator = [[VerticalSeparatorView alloc] init];
    [firstView.superview addSubview:separator];
    separator.firstView = firstView;
    separator.secondView = secondView;

    [NSLayoutConstraint activateConstraints:@[
        [separator.widthAnchor constraintEqualToConstant:kTotalWidth],
        [separator.superview.topAnchor constraintEqualToAnchor:separator.topAnchor],
        [separator.superview.bottomAnchor constraintEqualToAnchor:separator.bottomAnchor],
        [firstView.rightAnchor constraintEqualToAnchor:separator.leftAnchor constant:kMargin],
        [secondView.leftAnchor constraintEqualToAnchor:separator.rightAnchor constant:-kMargin],
    ]];

    separator.leftConstraint = [separator.leftAnchor constraintEqualToAnchor:separator.superview.leftAnchor constant:0]; // it doesn't matter what the constant is, because it hasn't been enabled

    return separator;
}

In the touch handling code, you were still referencing y, whereas you now want to refer to x:

- (void)updateTopConstraintOnBasisOfTouch:(UITouch *)touch {
    // calculate where separator should be moved to

    CGFloat x = self.oldX + [touch locationInView:self.superview].x - self.firstTouch.x;

    // make sure the views above and below are not too small

    x = MAX(x, self.firstView.frame.origin.x + kMinWidth - kMargin);
    x = MIN(x, self.secondView.frame.origin.x + self.secondView.frame.size.width - (kMargin + kMinWidth));

    // set constraint

    self.leftConstraint.constant = x;
}