dotnet/wpf · error · ArgumentException

SR.Format(SR.Stylus_IndexOutOfRange…

Error message

SR.Format(SR.Stylus_IndexOutOfRange, index.ToString(System.Globalization.CultureInfo.InvariantCulture))

What it means

TabletDeviceCollection's indexer throws ArgumentException (SR.Stylus_IndexOutOfRange with the index formatted invariantly) when the index is negative or >= Count. Note it throws ArgumentException rather than the more conventional ArgumentOutOfRangeException.

Solutions

1. Check index against Count before indexing: if (index >= 0 && index < tablets.Count)
2. Iterate with foreach instead of manual indexing
3. Re-fetch the collection rather than caching indices across device changes

Example fix

// before
var device = Tablet.TabletDevices[i]; // i may be stale
// after
if (i >= 0 && i < Tablet.TabletDevices.Count)
{
    var device = Tablet.TabletDevices[i];
}

if (index < 0 || index >= Tablet.TabletDevices.Count) return null;

try { var device = Tablet.TabletDevices[i]; }
catch (ArgumentException ex) when (ex.Message.Contains("index")) { /* refresh count and retry */ }

When it happens

Trigger: Indexing TabletDeviceCollection with index < 0 or index >= collection Count, e.g. tabletDevices[n] where n came from a count computed elsewhere.

Common situations: Off-by-one loops over tablet devices; caching a count from before a device was unplugged (device count changed between reads); iterating with an index from stale code.

Related errors

• captureMode
• captureMode
• IndexOutOfRangeException
• IndexOutOfRangeException
• InvalidOperationException

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e9813aae46e256d0. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Common/TabletDeviceCollection.cs:73

        /// of TabletDevices.
        /// </summary>
        /// <param name="array">destination array</param>
        /// <param name="index">position in destination array to begin copying</param>
        public void CopyTo(TabletDevice[] array, int index)
        {
            TabletDevices.CopyTo(array, index);
        }

        /// <summary>
        /// Retrieve the specified TabletDevice object from the collection.
        /// </summary>
        /// <param name="index">index of TabletDevice in collection to retrieve</param>
        public TabletDevice this[int index]
        {
            get
            {
                if (index >= Count || index < 0)
                    throw new ArgumentException(SR.Format(SR.Stylus_IndexOutOfRange, index.ToString(System.Globalization.CultureInfo.InvariantCulture)), nameof(index));

                return TabletDevices[index];
            }
        }

        /// <summary>
        /// Returns an object which can be used to lock during synchronization by collection users.
        /// <seealso cref="System.Collections.ICollection.SyncRoot"/>
        /// </summary>
        public object SyncRoot
        {
            get
            {
                return this;
            }
        }

        /// <summary>

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