dotnet/wpf · error · ArgumentException

The ApplicationGesture array must contain at least one…

Error message

The ApplicationGesture array must contain at least one member.

What it means

When setting GestureRecognizer.EnabledGestures, the value is funneled through GetApplicationGestureArrayAndVerify, which rejects an empty ApplicationGesture array with ArgumentException (SR.ApplicationGestureArrayLengthIsZero). An empty set is meaningless to the native recognizer, so it is disallowed up front.

Solutions

Always pass at least one ApplicationGesture (use ApplicationGesture.AllGestures to enable everything)
Check the array length before assigning and skip assignment if empty
To effectively disable gestures, unsubscribe from gesture events or dispose the recognizer instead
Throw or log a configuration error upstream when the gesture list computes to empty

Example fix

// before
recognizer.EnabledGestures = GetEnabledGestures(); // may be empty
// after
var gestures = GetEnabledGestures();
if (gestures.Length > 0) recognizer.EnabledGestures = gestures;

Defensive patterns

Strategy: validation

Validate before calling

if (gestures == null || gestures.Length == 0)
    throw new ArgumentException("At least one ApplicationGesture is required", nameof(gestures));

Type guard

static bool IsValidGestureSet(ApplicationGesture[] g) => g != null && g.Length > 0;

Try / catch

try { recognizer.EnabledGestures = gestures; }
catch (ArgumentException ex) { logger.LogError(ex, "Empty gesture set"); }

Prevention

Use ApplicationGesture.AllGestures when you want everything enabled
Never use an empty array to 'disable' gestures — remove the recognizer instead
Validate dynamically-built gesture lists before assignment

When it happens

Trigger: Assigning EnabledGestures an empty array or a collection whose count is 0 (e.g. a filtered list where all gestures were removed).

Common situations: Building the gesture list dynamically and forgetting the empty case; disabling all gestures by passing an empty array instead of removing the recognizer.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/75e5828e7d033632. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/GestureRecognizer/NativeRecognizer.cs:209

            //we need to make a disconnected copy
            ICollection<ApplicationGesture> collection = applicationGestures as ICollection<ApplicationGesture>;
            if (collection != null)
            {
                count = (uint)collection.Count;
            }
            else
            {
                foreach (ApplicationGesture gesture in applicationGestures)
                {
                    count++;
                }
            }

            // Cannot be empty
            if (count == 0)
            {
                // An empty array is not allowed.
                throw new ArgumentException(SR.ApplicationGestureArrayLengthIsZero, nameof(applicationGestures));
            }

            bool foundAllGestures = false;
            List<ApplicationGesture> gestures = new List<ApplicationGesture>();
            foreach (ApplicationGesture gesture in applicationGestures)
            {
                if (!ApplicationGestureHelper.IsDefined(gesture))
                {
                    throw new ArgumentException(SR.ApplicationGestureIsInvalid, nameof(applicationGestures));
                }

                //check for allgestures
                if (gesture == ApplicationGesture.AllGestures)
                {
                    foundAllGestures = true;
                }

                //check for dupes

View on GitHub (pinned to 81131a70a4)