dotnet/maui · error · InvalidOperationException

Cannot convert "{0}" into {1}

Error message

Cannot convert "{0}" into {1}

What it means

The TextDecorationsConverter throws InvalidOperationException when ConvertFrom receives a value whose ToString() is null. Because the converter calls value?.ToString() and then checks for null, this is reached when the source object's ToString returns null — an edge case for null-valued input passed as a non-null object. The message formats the null string and the TextDecorations type.

Source

Thrown at src/Controls/src/Core/DecorableTextElement.cs:28

		public static readonly BindableProperty TextDecorationsProperty = BindableProperty.Create(nameof(IDecorableTextElement.TextDecorations), typeof(TextDecorations), typeof(IDecorableTextElement), TextDecorations.None);
	}

	/// <summary>A <see cref="System.ComponentModel.TypeConverter"/> subclass that can convert between a string and a <see cref="Microsoft.Maui.TextDecorations"/> object.</summary>
	public class TextDecorationConverter : TypeConverter
	{
		public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
			=> sourceType == typeof(string);

		public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destinationType)
			=> destinationType == typeof(string);

		public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
		{
			var strValue = value?.ToString();

			TextDecorations result = TextDecorations.None;
			if (strValue == null)
				throw new InvalidOperationException(string.Format("Cannot convert \"{0}\" into {1}", strValue, typeof(TextDecorations)));

			var valueArr = strValue.Split(',');

			if (valueArr.Length <= 1)
				valueArr = strValue.Split(' ');

			foreach (var item in valueArr)
			{
				if (Enum.TryParse(item.Trim(), true, out TextDecorations textDecorations))
					result |= textDecorations;
				else if (item.Equals("line-through", StringComparison.OrdinalIgnoreCase))
					result |= TextDecorations.Strikethrough;
				else
					throw new InvalidOperationException(string.Format("Cannot convert \"{0}\" into {1}", item, typeof(TextDecorations)));
			}

			return result;
		}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Pass a string literal or comma/space-separated decoration names (e.g. 'underline', 'strikethrough', 'line-through').
2. Ensure any custom source object's ToString() never returns null.
3. Avoid routing null values into TextDecorations properties; use a fallback value.

Example fix

// before
label.TextDecorations = (TextDecorations)converter.ConvertFrom(null, culture, objWithNullToString);

// after
label.TextDecorations = TextDecorations.None; // explicit default

// Avoid passing values whose ToString() is null.
var s = value?.ToString();
if (s is null) throw new ArgumentException("value.ToString() returned null; cannot convert to TextDecorations.");

When it happens

Trigger: Passing an object whose ToString() implementation returns null (rare), or passing a null boxed value through a path that boxes it. The strValue==null guard is the only way to reach this throw.

Common situations: Custom types overriding ToString to return null; binding a null-valued non-string source to a TextDecorations property via the converter.

Related errors

• Cannot convert "{0}" into {1}
• Implement INativeElementView on cell renderer: {ContentCell.
• No UIViewController found to present.
• You MUST invoke LoadApplication () before calling base.Finis
• call Forms.Init() before this

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/df3052c930e715fe. Report an issue: GitHub.