dotnet/maui · error · BuildException

XC0040

XC0040

Error message

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

What it means

XamlC error XC0040 from ColumnDefinitionCollectionTypeConverter (used by Grid.ColumnDefinitions). The converter only proceeds when the value is non-whitespace; each comma-separated part is then parsed as a GridLength. An empty or whitespace-only value is rejected with XC0040. (A malformed individual part would instead fail inside GridLengthTypeConverter.)

Source

Thrown at src/Controls/src/Build.Tasks/CompiledConverters/ColumnDefinitionCollectionTypeConverter.cs:41

				yield return Create(Newarr, module.ImportReference(context.Cache, ("Microsoft.Maui.Controls", "Microsoft.Maui.Controls", "ColumnDefinition")));
				for (var i = 0; i < parts.Length; i++)
				{
					yield return Create(Dup);
					yield return Create(Ldc_I4, i);
					foreach (var instruction in gridlengthconverter.ConvertFromString(parts[i], context, node))
						yield return instruction;
					yield return Create(Newobj, module.ImportCtorReference(context.Cache,
							type: ("Microsoft.Maui.Controls", "Microsoft.Maui.Controls", "ColumnDefinition"),
							parameterTypes: new[] { ("Microsoft.Maui", "Microsoft.Maui", "GridLength") }));
					yield return Create(Stelem_Ref);
				}
				yield return Create(Newobj, module.ImportCtorReference(context.Cache,
						type: ("Microsoft.Maui.Controls", "Microsoft.Maui.Controls", "ColumnDefinitionCollection"),
						paramCount: 1));
				yield break;

			}
			throw new BuildException(BuildExceptionCode.Conversion, node, null, value, typeof(ColumnDefinitionCollection));
		}
	}
}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Provide valid GridLength values separated by commas, e.g. ColumnDefinitions="*,2*,100".
2. If no explicit columns are needed, remove the ColumnDefinitions attribute.

Example fix

<!-- before -->
<Grid ColumnDefinitions="">
  ...
</Grid>

<!-- after -->
<Grid ColumnDefinitions="*,2*">
  ...
</Grid>

When it happens

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

Common situations: An empty attribute left after editing; a binding/placeholder that produced empty; XAML designer inserting a blank value.

Related errors

• XC0020
• XC0040
• XC0000
• XC0001
• Expected VisualStateGroup but found {parent.Parent}

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/67c863721c47dff9. Report an issue: GitHub.