WPF Window - Only allow horizontal resize

Question

I want to only allow my WPF window to be resized horizontally. How best can I achieve this?

Answer 1

Building on the answers from User3810621 and others, this can be turned into a reusable behavior which locks in the calculated sizes as min and/or max after the first content render:

namespace whatever.util.wpf.behaviors
{
    using System.Windows;
    using System.Windows.Interactivity;

    public class LockInitialSize : Behavior
    {
        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.ContentRendered += OnContentRendered;
        }

        protected override void OnDetaching()
        {
            // possibly detached before ever rendering
            AssociatedObject.ContentRendered -= OnContentRendered;
            base.OnDetaching();
        }

        private void OnContentRendered(object s, EventArgs e)
        {
            // Just once
            AssociatedObject.ContentRendered -= OnContentRendered;

            if (MinWidth)
            {
                AssociatedObject.MinWidth = AssociatedObject.ActualWidth;
            }
            /// ... MaxWidth, MinHeight, MaxHeight
        }

        #region MinWidth Property

        public bool MinWidth
        {
            get => (bool)GetValue(MinWidthProperty);
            set => SetValue(MinWidthProperty, value);
        }

        public static readonly DependencyProperty MinWidthProperty =
            DependencyProperty.Register(nameof(MinWidth), typeof(bool), typeof(LockInitialSize));

        #endregion

        // ... MaxWidth, MinHeight, MaxHeight    
    }
}

The remaining, repetitive values are trivial and omitted for brevity.

Usage: