dotnet/maui · error · FormatException

Path contains an empty part

Error message

Path contains an empty part

What it means

Thrown while parsing the binding path string when, after splitting on '.' and trimming, a path part is the empty string. This indicates a malformed path such as leading/trailing/consecutive dots (e.g. "A..B", ".A", "A.").

Source

Thrown at src/Controls/src/Core/BindingExpression.cs:235

			string p = Path.Trim();

			var last = new BindingExpressionPart(this, ".");
			_parts.Add(last);

			if (p[0] == '.')
			{
				if (p.Length == 1)
					return;

				p = p.Substring(1);
			}

			string[] pathParts = p.Split(ExpressionSplit);
			for (var i = 0; i < pathParts.Length; i++)
			{
				string part = pathParts[i].Trim();
				if (part == string.Empty)
					throw new FormatException("Path contains an empty part");

				BindingExpressionPart indexer = null;

				int lbIndex = part.IndexOf("[", StringComparison.Ordinal);
				if (lbIndex != -1)
				{
					int rbIndex = part.Length - 1;
					if (part[rbIndex] != ']')
						throw new FormatException("Indexer did not contain closing bracket");

					int argLength = rbIndex - lbIndex - 1;
					if (argLength == 0)
						throw new FormatException("Indexer did not contain arguments");

					string argString = part.Substring(lbIndex + 1, argLength);
					indexer = new BindingExpressionPart(this, argString, true);

					part = part.Substring(0, lbIndex);

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Sanitize the path: remove empty segments and leading/trailing dots before constructing the Binding.
2. Build paths with a helper that joins non-empty parts with '.'.
3. Validate path tokens against a property whitelist and reject malformed input early.

Example fix

// before
var path = $"{parent}.{child}"; // child is "" -> "Parent."
var b = new Binding(path);

// after
var parts = new[] { parent, child }.Where(s => !string.IsNullOrWhiteSpace(s));
var path = string.Join(".", parts);
var b = new Binding(path);

static string SanitizePath(string raw)
{
    var parts = raw.Split('.').Where(p => !string.IsNullOrWhiteSpace(p));
    return string.Join(".", parts);
}
var binding = new Binding(SanitizePath(rawPath));

static bool IsValidBindingPath(string p) =>
    !string.IsNullOrWhiteSpace(p) &&
    p.Split('.').All(seg => !string.IsNullOrWhiteSpace(seg));

When it happens

Trigger: Constructing new Binding("A..B"), new Binding(".Name"), new Binding("Name."), or any path where Split('.') yields an empty token. Dynamically building path strings with string concatenation that leaves stray dots.

Common situations: Building paths from nullable/optional segments (string.Format("{0}.{1}") where a segment is empty). Reading paths from config/JSON with trailing dots. User input feeding a binding path.

Related errors

• Indexer did not contain closing bracket
• Indexer did not contain arguments
• mode is not a valid BindingMode
• RootComponent requires a value for its Selector property, bu
• RootComponent requires a value for its ComponentType propert

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/92cca697a76d1d24. Report an issue: GitHub.