dotnet/wpf · error · NotSupportedException

SR.Track_SameButtons

Error message

SR.Track_SameButtons

What it means

Track.DecreaseButton setter throws NotSupportedException when the value being assigned is the same object already stored in IncreaseButton. A Track must never use one Button for both the increase and decrease repeat buttons, so the assignment is rejected before UpdateComponent runs.

Solutions

1. Provide two distinct Button instances (or two distinct template parts) for DecreaseButton and IncreaseButton.
2. In a custom template, define two separate RepeatButton parts with different names/styles and bind each to its Track property.
3. If one visual style is desired, duplicate the element with shared style rather than sharing the instance.

Example fix

// before
<Track.DecreaseButton>
  <RepeatButton x:Name="btn" Command="ScrollBar.DecreaseSmall"/>
</Track.DecreaseButton>
<Track.IncreaseButton>
  <RepeatButton Command="{Binding Command, ElementName=btn}"/> <!-- same instance pattern -> throws when identical -->
</Track.IncreaseButton>
// after
<Track.DecreaseButton>
  <RepeatButton Command="ScrollBar.DecreaseSmall"/>
</Track.DecreaseButton>
<Track.IncreaseButton>
  <RepeatButton Command="ScrollBar.IncreaseSmall"/> <!-- distinct instance -->
</Track.IncreaseButton>

if (newButton != null && !ReferenceEquals(newButton, track.IncreaseButton)) track.DecreaseButton = newButton;

static bool CanSetDecreaseButton(Track track, Button value) => value == null || !ReferenceEquals(track.IncreaseButton, value);

try
{
    track.DecreaseButton = value;
}
catch (NotSupportedException)
{
    // same instance as IncreaseButton; create a distinct button
}

When it happens

Trigger: x:Name-ing or assigning the same Button instance (or template-resolved reference) to both DecreaseButton and IncreaseButton on a Track, typically via a custom ScrollBar/Slider template that reuses one button element.

Common situations: Minimal custom ScrollBar templates where a developer gives both repeat-button slots the same named part; code-behind that wires one button object to both properties.

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

• By default, ToolTip property does not support ToolTip…
• Cannot convert from type.
• Cannot convert to type.
• Cannot convert to type.
• CollectionIsFixedSize

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/5f2807562e6c6b87. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/Track.cs:164

                InvalidateMeasure();
                InvalidateArrange();
            }
        }

        /// <summary>
        /// The RepeatButton used to decrease the Value
        /// </summary>
        public RepeatButton DecreaseRepeatButton
        {
            get
            {
                return _decreaseButton;
            }
            set
            {
                if (_increaseButton == value)
                {
                    throw new NotSupportedException(SR.Track_SameButtons);
                }
                UpdateComponent(_decreaseButton, value);
                _decreaseButton = value;

                if (_decreaseButton != null)
                {
                    CommandManager.InvalidateRequerySuggested(); // Should post an idle queue item to update IsEnabled on button
                }
            }
        }

        /// <summary>
        /// The Thumb in the Track
        /// </summary>
        public Thumb Thumb
        {
            get
            {

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