dotnet/maui · error · ArgumentException

No file exists at "{0}"

Error message

No file exists at "{0}"

What it means

Verify.FileExists throws ArgumentException when File.Exists(filePath) returns false. It combines IsNeitherNullNorEmpty on the path with a filesystem existence check, so the message formats the offending path. It is a precondition guard for APIs that require a real file on disk.

Source

Thrown at src/Compatibility/Core/src/WPF/Microsoft.Windows.Shell/Standard/Verify.cs:297

			Verify.IsNotNull(type, "type");
			Verify.IsNotNull(interfaceType, "interfaceType");

			if (type.GetInterface(interfaceType.Name) == null)
			{
				Assert.Fail();
				throw new ArgumentException("The type of this parameter does not support a required interface", parameterName);
			}
		}

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void FileExists(string filePath, string parameterName)
		{
			Verify.IsNeitherNullNorEmpty(filePath, parameterName);
			if (!File.Exists(filePath))
			{
				Assert.Fail();
				throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, "No file exists at \"{0}\"", filePath), parameterName);
			}
		}

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		internal static void ImplementsInterface(object parameter, Type interfaceType, string parameterName)
		{
			Assert.IsNotNull(parameter);
			Assert.IsNotNull(interfaceType);
			Assert.IsTrue(interfaceType.IsInterface);

			bool isImplemented = false;
			foreach (var ifaceType in parameter.GetType().GetInterfaces())
			{
				if (ifaceType == interfaceType)
				{
					isImplemented = true;
					break;

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Verify File.Exists(path) at the call site before invoking the API.
2. Resolve paths to absolute with Path.GetFullPath and log the resolved path for debugging.
3. Check the deployment package includes the file and the working directory is correct.

Example fix

// before
loader.Load(templatePath); // file may not exist

// after
var fullPath = Path.GetFullPath(templatePath);
if (!File.Exists(fullPath))
{
    throw new FileNotFoundException($"Template not found: {fullPath}", fullPath);
}
loader.Load(fullPath);

// Pre-check: file must exist
var fullPath = Path.GetFullPath(filePath);
if (!File.Exists(fullPath))
{
    throw new FileNotFoundException($"File not found: {fullPath}", fullPath);
}
SomeApi(fullPath);

When it happens

Trigger: Calling a method guarded by Verify.FileExists(filePath, paramName) where the file does not exist at the given path. The guard fires before any attempt to open or read the file.

Common situations: Relative path resolved against the wrong working directory; missing deployment artifact; user-supplied path with a typo; file deleted between a prior check and the call; path environment differences between dev and production.

Related errors

• The parameter cannot be either null or empty.
• The parameter cannot be either null or empty or consist only
• The parameter must not be the default value.
• The parameter must be null.
• The URI must be absolute.

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/3c863a1e3023d532. Report an issue: GitHub.