UIElement.DesiredSize Property

July 28, 2014

Gets the size that this UIElement computed during the measure pass of the layout process.

Namespace:  System.Windows
Assembly:  System.Windows (in System.Windows.dll)

'Declaration
Public ReadOnly Property DesiredSize As Size

Property Value

Type: System.Windows.Size
The size that this UIElement computed during the measure pass of the layout process.

DesiredSize values are set by the layout system as part of calls to Measure.

DesiredSize values are useful if you are implementing layout override behavior, in particular during the arrange pass. Depending on the scenario, DesiredSize might be fully respected by your layout logic, constraints on DesiredSize might be applied, and such constraints might also change other characteristics of either the parent or child in layout. For example, a control that supports scrollable regions (but chooses not to derive from controls that already enable scrollable regions) could compare available size to DesiredSize. The control could then set an internal state that enabled scrollbars in the UI for that control. Or, DesiredSize could potentially also be ignored in certain layout scenarios.

You would not typically get the value of DesiredSize outside of a context where your code has already called Measure on that same element as part of the measure pass of layout, or called something that initiates a full layout pass such as UpdateLayout. Otherwise, there is no guarantee that the value held by DesiredSize is relevant.

The following example queries DesiredSize as part of the child iteration for an ArrangeOverride implementation.


'Second arrange all children and return final size of panel 
Protected Overloads Overrides Function ArrangeOverride(ByVal finalSize As Size) As Size
    'Get the collection of children 
    Dim mychildren As UIElementCollection = Children

    'Get total number of children 
    Dim count As Integer = mychildren.Count

    'Arrange children 
    'We're only allowing 9 children in this panel. More children will get a 0x0 layout slot. 
    Dim i As Integer
    For i = 0 To 8

        'Get (left, top) origin point for the element in the 3x3 block 
        Dim cellOrigin As Point = GetOrigin(i, 3, New Size(100, 100))

        'Arrange child 
        'Get desired height and width. This will not be larger than 100x100 as set in MeasureOverride. 
        Dim dw As Double = mychildren(i).DesiredSize.Width
        Dim dh As Double = mychildren(i).DesiredSize.Height


        mychildren(i).Arrange(New Rect(cellOrigin.X, cellOrigin.Y, dw, dh))
    Next
    For i = 9 To count - 1

        'Give the remaining children a 0x0 layout slot 
        mychildren(i).Arrange(New Rect(0, 0, 0, 0))
    Next


    'Return final size of the panel 
    Return New Size(300, 300)
End Function

'Calculate point origin of the Block you are in 
Protected Function GetOrigin(ByVal blockNum As Integer, ByVal blocksPerRow As Integer, ByVal itemSize As Size) As Point
    'Get row number (zero-based) 
    Dim row As Integer = CInt(Math.Floor(blockNum / blocksPerRow))

    'Get column number (zero-based) 
    Dim column As Integer = blockNum - blocksPerRow * row

    'Calculate origin 
    Dim origin As New Point(itemSize.Width * column, itemSize.Height * row)
    Return origin

End Function


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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