dotnet/wpf · error · ArgumentException

Width and Height cannot be negative.

Error message

Width and Height cannot be negative.

What it means

SizeBox is an internal WPF helper that boxes a (width, height) pair so common sizes can be cached and reused without allocation. Its constructor enforces the WPF Size/Rect invariant that dimensions are non-negative, throwing ArgumentException (SR.Rect_WidthAndHeightCannotBeNegative) when either width or height is negative.

Solutions

  1. Clamp computed dimensions with Math.Max(0, value) before constructing the size
  2. Validate width/height at the calculation site and treat negative results as 'no size' rather than a size
  3. Fix the upstream arithmetic that yields the negative dimension

Example fix

// before
var box = new SizeBox(availableWidth - margin, availableHeight - margin); // can be negative

// after
var w = Math.Max(0, availableWidth - margin);
var h = Math.Max(0, availableHeight - margin);
var box = new SizeBox(w, h);
Defensive patterns

Strategy: validation

Validate before calling

if (double.IsNaN(width) || double.IsNaN(height) || width < 0 || height < 0)
{
    width  = Math.Max(0, width);
    height = Math.Max(0, height);
}

Type guard

static bool IsValidBoxedSize(double width, double height)
    => !double.IsNaN(width) && !double.IsNaN(height) && width >= 0 && height >= 0;

Try / catch

try
{
    var box = new SizeBox(width, height);
}
catch (ArgumentException)
{
    // negative dimension from layout math; clamp and retry
    var box = new SizeBox(Math.Max(0, width), Math.Max(0, height));
}

Prevention

When it happens

Trigger: Constructing a SizeBox with width < 0 or height < 0 — typically a computed negative dimension (e.g., available size minus larger padding/margins) passed into the boxing helper.

Common situations: Layout/measure/arrange math producing negative sizes (subtracting margins or decorations that exceed available space); generalizing code that boxes negative placeholder sizes; NaN/negative results from custom panels flowing into cached-size paths.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/780bf7b843deaf0c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/KnownBoxes.cs:14

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Windows;

namespace MS.Internal.KnownBoxes
{
    internal class SizeBox
    {
        internal SizeBox(double width, double height)
        {
            if (width < 0 || height < 0)
            {
                throw new System.ArgumentException(SR.Rect_WidthAndHeightCannotBeNegative);
            }

            _width = width;
            _height = height;
        }

        internal SizeBox(Size size): this(size.Width, size.Height) {}

        internal double Width  
        { 
            get 
            { 
                return _width; 
            }
            set
            {
                if (value < 0)
                {

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