With Auto Layout, how do I make a UIImageView's size dynamic depending on the image?

Question

I want my UIImageView to grow or shrink depending on the size of what the actual image it\'s displaying is. But I want it to stay vertically centered and 10pts

Answer 1

If anyone comes here wanting a simple copy+paste for Xamarin heres @algal's code (with some of @alexander's changes) converted to .Net

Also I've changed it to constrain the Height based on the Width + Aspect Ratio as that fit all of my use cases.

/// 

///  UIImage view that will set the height correct based on the current
///  width and the aspect ratio of the image.
///  https://stackoverflow.com/a/42654375/9829321
/// 
public class UIAspectFitImageView : UIImageView
{
    private NSLayoutConstraint _heightConstraint;

    public override UIImage Image
    {
        get => base.Image;
        set
        {
            base.Image = value;
            UpdateAspectRatioConstraint();
        }
    }

    public UIAspectFitImageView()
        => Setup();

    public UIAspectFitImageView(UIImage image) : base(image)
        => Setup();

    public UIAspectFitImageView(NSCoder coder) : base(coder)
        => Setup();

    public UIAspectFitImageView(CGRect frame) : base(frame)
        => Setup();

    public UIAspectFitImageView(UIImage image, UIImage highlightedImage) : base(image, highlightedImage)
        => Setup();

    private void Setup()
    {
        ContentMode = UIViewContentMode.ScaleAspectFit;
        UpdateAspectRatioConstraint();
    }

    private void UpdateAspectRatioConstraint()
    {
        if (Image != null && Image.Size.Width != 0)
        {
            var aspectRatio = Image.Size.Height / Image.Size.Width;

            if (_heightConstraint?.Multiplier != aspectRatio)
            {
                if (_heightConstraint != null)
                {
                    RemoveConstraint(_heightConstraint);
                    _heightConstraint.Dispose();
                    _heightConstraint = null;
                }

                _heightConstraint = HeightAnchor.ConstraintEqualTo(WidthAnchor, aspectRatio);
                _heightConstraint.Priority = 1000;
                _heightConstraint.Active = true;
                AddConstraint(_heightConstraint);
            }
        }
    }
}