Assembly: System.Windows (in System.Windows.dll)
Be sure you only rely on this property value when the passes that are involved in layout and in rendering for the relevant FrameworkElement are complete. is a calculated value, and there can be multiple or incremental reported changes to the value because of operations by the layout system. If you get the value while layout is still iterating, the layout system might still be calculating the required measure of space for child objects, constraints by the parent object, and so on. Because the value is based on an actual rendering pass, it may lag slightly behind the set value of properties like Height, which can be the basis of the input change.
The return value of might also reflect the influence of layout rounding. Certain containers (notably TextBlock) might return values that are not rounded, regardless of layout rounding settings.
For purposes of ElementName binding, does not post updates when it changes (due to its asynchronous and run-time calculated nature). Do not attempt to use as a binding source for an ElementName binding. If you have a scenario that requires updates based on , use a SizeChanged handler.