Gets a value indicating whether the current size returned by layout measure is valid.
Assembly: PresentationCore (in PresentationCore.dll)
You can force measurement and arrangement to be invalidated by calling InvalidateMeasure on this element (or any parent element up the visual tree). This designates the layout for recomposition asynchronously, occurring at a time determined by the layout system. Alternatively, you could make an immediate call to UpdateLayout. However, you should only call UpdateLayout if it is likely that no further invalidations are pending (a large number of unnecessarily forced updates will have performance consequences).
If is false, IsArrangeValid must also be false (by the enforced logic of the layout process, arrangement cannot be valid without measurement first being valid).