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

If you set the MinHeight and MaxHeight attributes of the window to the desired height the window will have a fixed height

Answer 2

It's kind of a pain. Basically you need to set up a hook function to process windows messages. Then you would catch the WM_SIZING (0x0214) message and modify the parameters so that the horizontal dimension could not be changed.

Pete Brown also has some great info on this topic on his blog.

Answer 3

You could try databinding to the size of the window, and then setting the size back to the old value whenever the vertical dimension is changed.

Answer 4

If you want to use the MinHeight and MaxHeight approach but still allow the window to automatically size itself to fit the size of its content:

To allow automatic content sizing don't use the Loaded event. Use the ContentRendered event instead.

Answer 5

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<Window>
    {
        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:

<Window ...
     xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
     xmlns:behaviors="clr-namespace:whatever.util.wpf.behaviors;assembly=whatever"
     SizeToContent="Height"
     ...>
    <i:Interaction.Behaviors>
        <behaviors:LockInitialSize MinHeight="True" MaxHeight="True" />
    </i:Interaction.Behaviors>

Answer 6

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<UIElement>
{
    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<MouseButtonEventArgs>(AssociatedObject, "MouseLeftButtonDown")
                                    .Select(e => e.EventArgs.GetPosition(AssociatedObject));

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

        var mouseMove = Observable.FromEventPattern<MouseEventArgs>(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:

<Border Background="Gray" 
        Height="10" 
        Cursor="SizeNS"
        Grid.ColumnSpan="2">
    <i:Interaction.Behaviors>
        <b:VerticalResizeWindowBehavior MinHeight="600"/>
    </i:Interaction.Behaviors>
</Border>

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.