lepoco/wpfui · critical · InvalidOperationException

The `_desiredWidth` field was not found.

Error message

The `_desiredWidth` field was not found.

What it means

Thrown lazily (on first access of DesiredWidthField) when reflection over the base System.Windows.Controls.GridViewColumn fails to locate the private instance field '_desiredWidth'. WPF UI's GridViewColumn extension clamps column width via this field; if the .NET / WPF runtime renames or removes it, the feature cannot function and the library fails fast. This is a version-compatibility break, not a usage error.

Source

Thrown at src/Wpf.Ui/Controls/GridView/GridViewColumn.cs:36

///         <ui:GridView>
///             <ui:GridViewColumn
///                 MinWidth="100"
///                 MaxWidth="200"
///                 DisplayMemberBinding="{Binding FirstName}"
///                 Header="First Name" />
///         </ui:GridView>
///     </ui:ListView.View>
/// </ui:ListView>
/// </code>
/// </example>
public class GridViewColumn : System.Windows.Controls.GridViewColumn
{
    // use reflection to get the `_desiredWidth` private field.
    private static readonly Lazy<FieldInfo> _desiredWidthField = new(() =>
        typeof(System.Windows.Controls.GridViewColumn).GetField(
            "_desiredWidth",
            BindingFlags.NonPublic | BindingFlags.Instance
        ) ?? throw new InvalidOperationException("The `_desiredWidth` field was not found.")
    );

    private static FieldInfo DesiredWidthField => _desiredWidthField.Value;

    // use reflection to get the `UpdateActualWidth` private method.
    private static readonly Lazy<MethodInfo> _updateActualWidthMethod = new(() =>
    {
        MethodInfo methodInfo =
            typeof(System.Windows.Controls.GridViewColumn).GetMethod(
                "UpdateActualWidth",
                BindingFlags.NonPublic | BindingFlags.Instance
            ) ?? throw new InvalidOperationException("The `UpdateActualWidth` method was not found.");
        return methodInfo;
    });

    private static MethodInfo UpdateActualWidthMethod => _updateActualWidthMethod.Value;

    /// <summary>

View on GitHub (pinned to ffebacd610)

Solutions

1. Pin to a .NET / WPF version known to ship the '_desiredWidth' field (check the release the library targets).
2. Avoid triggering the clamp path: do not rely on ui:GridViewColumn MinWidth/MaxWidth and use the stock behavior instead.
3. If you control deployment, disable AOT/trimming for the WPF assembly so reflection metadata is preserved.
4. Report the break upstream so the field name / lookup can be updated for the new runtime.

try { col.UpdateDesiredWidth(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("_desiredWidth"))
{
    // Runtime incompatibility: fall back to stock GridViewColumn behavior
    Logger.Warn($"GridViewColumn reflection failed on this runtime: {ex.Message}");
}

When it happens

Trigger: Running the MinWidth/MaxWidth clamping feature (first call to UpdateDesiredWidth) on a .NET / WPF build where the internal field '_desiredWidth' has been renamed or removed; targeting a future .NET version that refactored GridViewColumn internals.

Common situations: Upgrading the .NET target framework (e.g. to a preview or post-.NET-8 build) where WPF internals changed; running on a trimmed/AOT-compiled binary where reflection metadata for private members was stripped; using a custom WPF fork.

Related errors

• The `UpdateActualWidth` method was not found.
• Failed to get the current `_desiredWidth`.
• Unable to get or create instance of {viewItem.TargetPageType
• Failed to create instance of the page
• The {pageType} page does not have a parameterless constructo

AI-assisted analysis of lepoco/wpfui@ffebacd610 (2026-08-13). Data as JSON: /api/errors/a7f4983ff0ac3a5b. Report an issue: GitHub.