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Track.ViewportSize Property

Gets or sets the size of the part of the scrollable content that is visible. This is a dependency property.

Namespace:  System.Windows.Controls.Primitives
Assembly:  PresentationFramework (in PresentationFramework.dll)

public double ViewportSize { get; set; }
<object ViewportSize="double" .../>

Property Value

Type: System.Double
The size of the visible area of the scrollable content. The default is Double.NaN, which means that the content size is not defined.

Identifier field


Metadata properties set to true


The value of the ViewportSize property is used to calculate the size of the Thumb control in a ScrollBar when the ViewportSize is not Double.NaN. For more information, see the remarks for the Thumb property.

To explicitly define the size of the Thumb, create an object that derives from the Track class and provide overrides for MeasureOverride and ArrangeOverride.

If you implement a Track as part of a ScrollBar control and you do not explicitly set the Track.ViewportSize property, the Track.ViewportSize property binds to the ScrollBar.ViewportSize property.

The value of the ViewportSize property of a Track control that is implemented in a Slider control is always Double.NaN, because the Thumb control does not change size.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0