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

The following solution allows you to leave SizeToContent intact,
doesn't require Win32 Interop or code behind in your Window:

It does rely on Reactive Extensions

In the Package Manager run:

Install-Package System.Reactive

Then you start by creating a new Behavior:

public class VerticalResizeWindowBehavior : Behavior
{
    public static readonly DependencyProperty MinHeightProperty = DependencyProperty.Register("MinHeight", typeof(double), typeof(VerticalResizeWindowBehavior), new PropertyMetadata(600.0));
    public double MinHeight
    {
        get { return (double)GetValue(MinHeightProperty); }
        set { SetValue(MinHeightProperty, value); }
    }

    protected override void OnAttached()
    {
        base.OnAttached();

        var window = Window.GetWindow(AssociatedObject);
        var mouseDown = Observable.FromEventPattern(AssociatedObject, "MouseLeftButtonDown")
                                    .Select(e => e.EventArgs.GetPosition(AssociatedObject));

        var mouseUp = Observable.FromEventPattern(AssociatedObject, "MouseLeftButtonUp")
                                .Select(e => e.EventArgs.GetPosition(AssociatedObject));

        var mouseMove = Observable.FromEventPattern(AssociatedObject, "MouseMove")
                                    .Select(e => e.EventArgs.GetPosition(AssociatedObject));

        var q = from start in mouseDown
                from position in mouseMove.TakeUntil(mouseUp)
                select new { X = position.X - start.X, Y = position.Y - start.Y };

        mouseDown.Subscribe(v => AssociatedObject.CaptureMouse());
        mouseUp.Subscribe(v => AssociatedObject.ReleaseMouseCapture());

        q.ObserveOnDispatcher().Subscribe(v =>
        {
            var newHeight = window.Height + v.Y;
            window.Height = newHeight < MinHeight ? MinHeight : newHeight;                
        });
    }
}

Then you add a UIElement at the bottom of your Window and apply the Behavior:

Set the following Properties on your Window:

ResizeMode="NoResize"
SizeToContent="Width"

Note: In this example, the user is allowed to resize Vertically but not Horizontally
You can easily change the code to allow the opposite, or add properties
to make it configurable.