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) XMLNS for XAML: http://schemas.microsoft.com/winfx/2006/xaml/presentation, http://schemas.microsoft.com/netfx/2007/xaml/presentation
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.