When overridden in a derived class, provides measurement logic for sizing this element properly, with consideration of the size of any child element content.
Assembly: PresentationCore (in PresentationCore.dll)
'Declaration Protected Overridable Function MeasureCore ( _ availableSize As Size _ ) As Size
- Type: System.Windows.Size
The available size that the parent element can allocate for the child.
Return ValueType: System.Windows.Size
The desired size of this element in layout.
It is more common to derive an element from FrameworkElement rather than UIElement. If you are deriving from FrameworkElement, note that an override of on FrameworkElement seals the method. Therefore, you only override as a means to alter layout measure characteristics if you derive from UIElement through an inheritance that does not include FrameworkElement. This might be the case if you are attempting to build your own implementation on the WPF core-level. Otherwise, if you are deriving from FrameworkElement, then the implementation template for Measure behavior is the FrameworkElement implementation of .MeasureOverride.
A parent element with child elements must call Measure on each child, otherwise these child elements are not sized or arranged and will effectively disappear from layout.Notes to Inheritors
Implementations must be able to process a value provided for availableSize that is infinite. An infinite value indicates no requested constraints, and effectively defers measurement choice to the parent element, through recursive Measure calls.
Implementations can consider the value provided for availableSize to be a soft constraint. The child element might specify a larger size, even if other aspects of application code were able to determine the current actual size of the parent element. The large size request is a convention that indicates that the child element is querying whether your parent element can support content scrolling within a content display region.
A typical override of follows this approximate pattern (there is not a built-in collection called VisualChildren; VisualChildren is a placeholder that represents whatever child collection your element maintains).
Protected Overrides Function MeasureCore(ByVal availableSize As Size) As Size For Each child As UIElement In VisualChildren child.Measure(availableSize) ' call some method on child that adjusts child size if needed _cache.StoreInfoAboutChild(child) Next child Dim desired As Size = CalculateBasedOnCache(_cache) Return desired End Function
You must call Measure on each child element.
Generally, your implementation should cache measurement information between the and ArrangeCore method calls in the same element.
Calling base implementations of is not required, but might be appropriate if the base implementation provides a desired layout capability.
Calls to Measure on child elements should pass either the same availableSize as the parent, or a subset of the area, depending on the type of layout the parent element supports. For example, it would be valid to remove the area for an element-specific border or padding, a scrollbar, or a custom control.