iPhone UIView - Resize Frame to Fit Subviews

Question

Shouldn\'t there be a way to resize the frame of a UIView after you\'ve added subviews so that the frame is the size needed to enclose all the subviews? If your subviews are

Answer 1

I needed to fit subviews had a negative origin point, and CGRectUnion is the ObjC way of doing it, honestly, as someone mentioned in the comments. First, let's see how it works:

As you can see below, we assume some subviews are lying outside, so we need to do two things to make this look good, without affecting the positioning of the subviews:

1. Move the frame of the view to the top left most position
2. Move the subviews the opposite direction to negate the effect.

A picture is worth a thousand words.

Code is worth a billion words. Here is the solution:

@interface UIView (UIView_Expanded)

- (void)resizeToFitSubviews;

@end

@implementation UIView (UIView_Expanded)

- (void)resizeToFitSubviews
{
    // 1 - calculate size
    CGRect r = CGRectZero;
    for (UIView *v in [self subviews])
    {
        r = CGRectUnion(r, v.frame);
    }

    // 2 - move all subviews inside
    CGPoint fix = r.origin;
    for (UIView *v in [self subviews])
    {
        v.frame = CGRectOffset(v.frame, -fix.x, -fix.y);
    }

    // 3 - move frame to negate the previous movement
    CGRect newFrame = CGRectOffset(self.frame, fix.x, fix.y);
    newFrame.size = r.size;

    [self setFrame:newFrame];
}

@end

---

I thought it would be fun to write in Swift 2.0 .. I was right!

extension UIView {

    func resizeToFitSubviews() {

        let subviewsRect = subviews.reduce(CGRect.zero) {
            $0.union($1.frame)
        }

        let fix = subviewsRect.origin
        subviews.forEach {
            $0.frame.offsetInPlace(dx: -fix.x, dy: -fix.y)
        }

        frame.offsetInPlace(dx: fix.x, dy: fix.y)
        frame.size = subviewsRect.size
    }
}

And the playground proof:

Notice the visualAidView doesn't move, and helps you see how the superview resizes while maintaining the positions of the subviews.

let canvas = UIView(frame: CGRect(x: 0, y: 0, width: 80, height: 80))
canvas.backgroundColor = UIColor.whiteColor()

let visualAidView = UIView(frame: CGRect(x: 5, y: 5, width: 70, height: 70))
visualAidView.backgroundColor = UIColor(white: 0.8, alpha: 1)
canvas.addSubview(visualAidView)

let superview = UIView(frame: CGRect(x: 15, y: 5, width: 50, height: 50))
superview.backgroundColor = UIColor.purpleColor()
superview.clipsToBounds = false
canvas.addSubview(superview)

[
    {
        let view = UIView(frame: CGRect(x: -10, y: 0, width: 15, height: 15))
        view.backgroundColor = UIColor.greenColor()
        return view
    }(),
    {
        let view = UIView(frame: CGRect(x: -10, y: 40, width: 35, height: 15))
        view.backgroundColor = UIColor.cyanColor()
        return view
    }(),
    {
        let view = UIView(frame: CGRect(x: 45, y: 40, width: 15, height: 30))
        view.backgroundColor = UIColor.redColor()
        return view
    }(),

].forEach { superview.addSubview($0) }