unoplatform/uno · error · XamlGenerationException

Unable to find the type '{_xClassName?.Namespace}.{_xClassNa

Error message

Unable to find the type '{_xClassName?.Namespace}.{_xClassName?.ClassName}'

What it means

Thrown in the x:Bind event GetTargetType() fallback (the final else) when the binding is NOT inside a template, _xClassName.Symbol is null, and no AutoGeneratedCodeBehindFiles entry exists for this file. The generator needs the page's type symbol to resolve the handler but cannot find it — meaning the x:Class type itself is unresolvable in the compilation. This couples an x:Bind outside a template to a valid, resolvable x:Class type.

Source

Thrown at src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.cs:3849

							}

							throw new XamlGenerationException("Unable to find x:DataType in enclosing DataTemplate for x:Bind event", bind);
						}

						return GetType(dataTypeObject.Value.ToString() ?? "");
					}
					else if (_xClassName?.Symbol is not null)
					{
						return _xClassName.Symbol;
					}
					else if (Generation.AutoGeneratedCodeBehindFiles.TryGetValue(_fileDefinition.UniqueID, out var autoGenBaseType))
					{
						// Use the XAML-derived base type when code-behind is auto-generated
						return autoGenBaseType;
					}
					else
					{
						throw new XamlGenerationException($"Unable to find the type '{_xClassName?.Namespace}.{_xClassName?.ClassName}'", bind);
					}
				}

				var targetType = GetTargetType(); // The type of the target object onto which the x:Bind path should be resolved
				var targetInstanceWeakRef = template.isInside
					// Use of __rootInstance is required to get the top-level DataContext, as it may be changed in the current visual tree by the user.
					? "(__rootInstance as global::Uno.UI.DataBinding.IWeakReferenceProvider).WeakReference"
					: $"({targetInstance} as global::Uno.UI.DataBinding.IWeakReferenceProvider).WeakReference";

				var method = ResolveXBindMethod(targetType, path, bind);
				var invokeTarget = (method.isStatic, template.isInside) switch
				{
					(true, _) => method.declaringType.GetFullyQualifiedTypeIncludingGlobal(), // If the method is static, the target onto which the method should be invoked is the declaringType itself
					(_, true) => $"((target.Target as {XamlConstants.Types.FrameworkElement})?.DataContext as {targetType.GetFullyQualifiedTypeIncludingGlobal()})?",
					_ => $"(target.Target as {targetType.GetFullyQualifiedTypeIncludingGlobal()})?"
				};

				var handler = RegisterChildSubclass(

View on GitHub (pinned to 0418340488)

Solutions

1. Ensure the code-behind partial class exists and its namespace+class exactly match x:Class in the XAML.
2. Confirm the code-behind file is included in the project (not excluded) and compiles.
3. If using auto-generated code-behind, verify the file is set up for it; otherwise add the missing partial class.
4. Rebuild after fixing namespace mismatches so Roslyn can resolve the type symbol.

Example fix

// before: x:Class="MyApp.MyPage" but code-behind is
namespace WrongApp { public partial class MyPage } 

// after: match namespaces
// XAML:  x:Class="MyApp.MyPage"
// C#:    namespace MyApp { public partial class MyPage }

# Ensure x:Class in each XAML matches an existing, compiling partial class
Get-ChildItem -Recurse -Filter *.xaml | ForEach-Object {
  $m = Select-String -Path $_.FullName -Pattern 'x:Class="([^"]+)"'
  if ($m) {
    $fqn = $m.Matches[0].Groups[1].Value
    $ns = $fqn.Substring(0, [Math]::Max(0,$fqn.LastIndexOf('.')))
    $cls = $fqn.Substring($fqn.LastIndexOf('.')+1)
    $cs = [System.IO.Path]::ChangeExtension($_.FullName, '.xaml.cs')
    if (-not (Test-Path $cs)) { Write-Warning "$($_.Name): x:Class=$fqn but no $cs found" }
    elseif (-not (Select-String -Path $cs -Pattern "class\s+$cls")) { Write-Warning "$cs: partial class $cls not found" }
  }
}

When it happens

Trigger: An {x:Bind} event on a page/control whose x:Class type does not compile or is not found by Roslyn (namespace/class mismatch, type in an excluded file, code-behind missing the partial class); using x:Bind in a file without proper code-behind generation.

Common situations: x:Class namespace does not match the code-behind namespace; the code-behind partial class was deleted or misnamed; the project uses auto-generated code-behind but the file is misconfigured; a file newly added without its .xaml.cs companion.

Related errors

• Unable to find class name for toplevel control
• Unable to find x:Class on the top level element
• The type '{objectDefinition.Type}' could not be found
• Unable to find type '{objectDefinition.Type}'
• x:Bind event path cannot be empty

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/e7f9352028400afb. Report an issue: GitHub.