What causes "Cannot convert value "{0}" to "{1}"." in dotnet/maui?

Provide a valid bounds value such as '0,0' or '0,0,100,50'.

dotnet/maui · error · BuildException

XC0040

XC0040

Error message

Cannot convert value "{0}" to "{1}".

What it means

XamlC error XC0040 from BoundsTypeConverter (used by AbsoluteLayout.LayoutBounds). An empty or null value is rejected immediately because a Bounds/Rect requires at least an x,y pair.

Source

Thrown at src/Controls/src/Build.Tasks/CompiledConverters/BoundsTypeConverter.cs:19

using System;
using System.Collections.Generic;
using System.Globalization;
using Microsoft.Maui.Controls.Build.Tasks;
using Microsoft.Maui.Controls.Xaml;
using Microsoft.Maui.Graphics;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace Microsoft.Maui.Controls.XamlC
{
	class BoundsTypeConverter : ICompiledTypeConverter
	{
		public IEnumerable<Instruction> ConvertFromString(string value, ILContext context, BaseNode node)
		{
			var module = context.Body.Method.Module;

			if (string.IsNullOrEmpty(value))
				throw new BuildException(BuildExceptionCode.Conversion, node, null, value, typeof(Rect));

			double x = -1, y = -1, w = -1, h = -1;
			bool hasX, hasY, hasW, hasH;
			var xywh = value.Split(',');

			if (xywh.Length != 2 && xywh.Length != 4)
				throw new BuildException(BuildExceptionCode.Conversion, node, null, value, typeof(Rect));

			hasX = (xywh.Length == 2 || xywh.Length == 4) && double.TryParse(xywh[0], NumberStyles.Number, CultureInfo.InvariantCulture, out x);
			hasY = (xywh.Length == 2 || xywh.Length == 4) && double.TryParse(xywh[1], NumberStyles.Number, CultureInfo.InvariantCulture, out y);
			hasW = xywh.Length == 4 && double.TryParse(xywh[2], NumberStyles.Number, CultureInfo.InvariantCulture, out w);
			hasH = xywh.Length == 4 && double.TryParse(xywh[3], NumberStyles.Number, CultureInfo.InvariantCulture, out h);

			if (!hasW && xywh.Length == 4 && string.Compare("AutoSize", xywh[2].Trim(), StringComparison.OrdinalIgnoreCase) == 0)
			{
				hasW = true;
				w = AbsoluteLayout.AutoSize;
			}

View on GitHub (pinned to f377ff1c5e)

Solutions

Provide a valid bounds value such as '0,0' or '0,0,100,50'.
If no explicit bounds are needed, remove the LayoutBounds attribute entirely.

Example fix

<!-- before -->
<BoxView LayoutBounds="" />

<!-- after -->
<BoxView LayoutBounds="0,0,100,50" />

Defensive patterns

Strategy: validation

Prevention

Never leave LayoutBounds empty; either set 'x,y' / 'x,y,w,h' or remove the attribute.
Run the XAML compiler (XamlC) in build so empty-value errors surface at compile time.
Avoid editor placeholders that resolve to empty strings.

When it happens

Trigger: LayoutBounds is set to an empty string or whitespace, e.g. LayoutBounds="" left over in markup.

Common situations: An empty attribute left in XAML after editing; a binding/placeholder that resolved to empty; tooling inserting a blank value.

Related errors

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/616523ee474ef669. Report an issue: GitHub.