dotnet/wpf · error · ArgumentException

SR.Format(SR.TextCompositionManager_NoInputManager…

Error message

SR.Format(SR.TextCompositionManager_NoInputManager, "composition")

What it means

TextCompositionManager.UnsafeStartComposition throws ArgumentException when the composition was not created with/attached to an InputManager (composition._InputManager is null). The manager needs the InputManager to route the composition events through the input pipeline.

Solutions

Create the composition via InputManager.Current.CreateTextComposition(device) so the InputManager is set.
Ensure the inputManager argument passed to the TextComposition constructor is non-null.
If testing, use InputManager.Current rather than a null or detached InputManager.

Example fix

// before
var composition = new TextComposition(null, device, "");
TextCompositionManager.StartComposition(composition);
// after
var composition = InputManager.Current.CreateTextComposition(device);
composition.SetText("");
TextCompositionManager.StartComposition(composition);

Defensive patterns

Strategy: validation

Validate before calling

if (composition.InputManager == null) throw new InvalidOperationException("Create the composition via InputManager.Current.CreateTextComposition first.");

Type guard

static bool CanStart(TextComposition c) => c?.Stage == TextCompositionStage.None;

Try / catch

try { TextCompositionManager.StartComposition(composition); } catch (ArgumentException ex) { /* composition not attached to an InputManager */ }

Prevention

Always use InputManager.Current.CreateTextComposition to build compositions.
Never construct TextComposition with a null inputManager argument.
Keep composition creation and usage on the same dispatcher/thread.

When it happens

Trigger: Calling TextCompositionManager.StartComposition (or triggering it via PreProcessInput/PostProcessInput) with a TextComposition whose InputManager is null — typically one constructed directly with a null inputManager argument.

Common situations: Constructing a TextComposition manually with new TextComposition(null, device, text) instead of via InputManager.CreateTextComposition, then passing it to StartComposition.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ce2a17db3b3fceda. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/TextCompositionManager.cs:314

        //------------------------------------------------------
        //
        //  Internal Events
        //
        //------------------------------------------------------

        //------------------------------------------------------
        //
        //  Private Methods
        //
        //------------------------------------------------------

        private static bool UnsafeStartComposition(TextComposition composition)
        {
            ArgumentNullException.ThrowIfNull(composition);

            if (composition._InputManager == null)
            {
                throw new ArgumentException(SR.Format(SR.TextCompositionManager_NoInputManager, "composition"));
            }

            if (composition.Stage != TextCompositionStage.None)
            {
                throw new ArgumentException(SR.Format(SR.TextCompositionManager_TextCompositionHasStarted, "composition"));
            }

            composition.Stage = TextCompositionStage.Started;
            TextCompositionEventArgs textargs = new TextCompositionEventArgs(composition._InputDevice, composition)
            {
                RoutedEvent = TextCompositionManager.PreviewTextInputStartEvent,
                Source = composition.Source
            };
            return composition._InputManager.ProcessInput(textargs);
        }

        private static bool UnsafeUpdateComposition(TextComposition composition)
        {

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