Drag separator to resize UIViews

Question

What would be to the best way of implementing an interface which consists of UIViews which are separated by a line, and the line can resize the views?

In it's simplest form, it could look like this:

----------------
|              |  
| View A       |
|              |
|--------------|  < line which can be moved up and down, resizing the views
|              |  
| View B       |   
|              |  
---------------- 

It could have many more views.

My first thought would be making the line a draggable UIView with something like Touches, which resized the views according to it's position, but I'm sure there must be a more elegant solution.

Answer 1

First, define a gesture that detects whether you started on a border, and if the gesture changes, moves said borders:

#import <UIKit/UIGestureRecognizerSubclass.h>

- (void)viewDidLoad
{
    [super viewDidLoad];

    // I use long press gesture recognizer so it's recognized immediately

    UILongPressGestureRecognizer *gesture = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    gesture.minimumPressDuration = 0.0;
    gesture.allowableMovement = CGFLOAT_MAX;
    gesture.delegate = self;
    [self.containerView addGestureRecognizer:gesture];
}

- (void)handlePan:(UILongPressGestureRecognizer *)gesture
{
    static NSArray *matches;
    static CGPoint firstLocation;

    if (gesture.state == UIGestureRecognizerStateBegan)
    {
        firstLocation = [gesture locationInView:gesture.view];
        matches = [BorderBeingDragged findBordersBeingDraggedForView:gesture.view fromLocation:firstLocation];
        if (!matches)
        {
            gesture.state = UIGestureRecognizerStateFailed;
            return;
        }
    }
    else if (gesture.state == UIGestureRecognizerStateChanged)
    {
        CGPoint location    = [gesture locationInView:gesture.view];
        CGPoint translation = CGPointMake(location.x - firstLocation.x, location.y - firstLocation.y);
        [BorderBeingDragged dragBorders:matches translation:translation];
    }
}

// if your subviews are scrollviews, you might need to tell the gesture recognizer
// to allow simultaneous gestures

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
    return TRUE;
}

Second, define a BordersBeingDragged class that does the detection of borders and the changing of borders:

typedef enum NSInteger {
    kBorderTypeNone   = 0,
    kBorderTypeLeft   = 1 << 0,
    kBorderTypeRight  = 1 << 1,
    kBorderTypeTop    = 1 << 2,
    kBorderTypeBottom = 1 << 3
} BorderType;

@interface BorderBeingDragged : NSObject

@property (nonatomic, weak) UIView *view;
@property (nonatomic) BorderType borderTypes;
@property (nonatomic) CGRect originalFrame;

@end

static CGFloat const kTolerance = 15.0;

@implementation BorderBeingDragged

+ (NSArray *)findBordersBeingDraggedForView:(UIView *)view fromLocation:(CGPoint)point
{
    NSMutableArray *matches = nil;

    for (UIView *subview in view.subviews)
    {
        BorderType types = kBorderTypeNone;
        CGRect frame = subview.frame;

        // test top and bottom borders

        if (point.x >= (frame.origin.x - kTolerance) &&
            point.x <= (frame.origin.x + frame.size.width + kTolerance))
        {
            if (point.y >= (frame.origin.y - kTolerance) && point.y <= (frame.origin.y + kTolerance))
                types |= kBorderTypeTop;
            else if (point.y >= (frame.origin.y + frame.size.height - kTolerance) && point.y <= (frame.origin.y + frame.size.height + kTolerance))
                types |= kBorderTypeBottom;
        }

        // test left and right borders

        if (point.y >= (frame.origin.y - kTolerance) &&
            point.y <= (frame.origin.y + frame.size.height + kTolerance))
        {
            if (point.x >= (frame.origin.x - kTolerance) && point.x <= (frame.origin.x + kTolerance))
                types |= kBorderTypeLeft;
            else if (point.x >= (frame.origin.x + frame.size.width - kTolerance) && point.x <= (frame.origin.x + frame.size.width + kTolerance))
                types |= kBorderTypeRight;
        }

        // if we found any borders, add it to our array of matches

        if (types != kBorderTypeNone)
        {
            if (!matches)
                matches = [NSMutableArray array];

            BorderBeingDragged *object = [[BorderBeingDragged alloc] init];
            object.borderTypes   = types;
            object.view          = subview;
            object.originalFrame = frame;

            [matches addObject:object];
        }
    }

    return matches;
}

+ (void)dragBorders:(NSArray *)matches translation:(CGPoint)translation
{
    for (BorderBeingDragged *object in matches)
    {
        CGRect newFrame = object.originalFrame;

        if (object.borderTypes & kBorderTypeLeft)
        {
            newFrame.origin.x   += translation.x;
            newFrame.size.width -= translation.x;
        }
        else if (object.borderTypes & kBorderTypeRight)
        {
            newFrame.size.width += translation.x;
        }

        if (object.borderTypes & kBorderTypeTop)
        {
            newFrame.origin.y    += translation.y;
            newFrame.size.height -= translation.y;
        }
        else if (object.borderTypes & kBorderTypeBottom)
        {
            newFrame.size.height += translation.y;
        }

        object.view.frame = newFrame;
    }
}

@end

Answer 2

You do essentially need to make the line-view draggable, but it doesn't need to be complicated.

1. Put viewA and viewB into a containerView
2. Add a pan gesture recognizer to the containerView configured for a single touch and set its delegate to your controller.
3. Implement gestureRecognizerShouldBegin: from the UIGestureRecognizerDelegate protocol and only allow it to begin if the touch in in the vicinity of the line-view.
4. In the gesture handler get the touch position in the containerView and set the line-view position and frames for viewA and viewB

That's pretty much it.