Sdílet prostřednictvím

UIElement.DesiredSize Property

  • Reference

Definition

Namespace:
Windows.UI.Xaml
Edit

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

public:
 property Size DesiredSize { Size get(); };
Size DesiredSize();
public Size DesiredSize { get; }
var size = uIElement.desiredSize;
Public ReadOnly Property DesiredSize As Size

Property Value

Size

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

Examples

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

// Second arrange all children and return final size of panel
protected override Size ArrangeOverride(Size finalSize)
{
    // Get the collection of children
    UIElementCollection mychildren = Children;

    // Get total number of children
    int count = mychildren.Count;

    // Arrange children
    // We're only allowing 9 children in this panel.  More children will get a 0x0 layout slot.
    int i;
    for (i = 0; i < 9; i++)
    {

        // Get (left, top) origin point for the element in the 3x3 block
        Point cellOrigin = 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.
        double dw = mychildren[i].DesiredSize.Width;
        double dh = mychildren[i].DesiredSize.Height;

        mychildren[i].Arrange(new Rect(cellOrigin.X, cellOrigin.Y, dw, dh));

    }

    // Give the remaining children a 0x0 layout slot
    for (i = 9; i < count; i++)
    {
        mychildren[i].Arrange(new Rect(0, 0, 0, 0));
    }


    // Return final size of the panel
    return new Size(300, 300);
}

'Second arrange all children and return final size of panel 
Protected 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 
    '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

Remarks

DesiredSize is typically checked as one of the measurement factors when you implement layout behavior overrides such as ArrangeOverride or MeasureOverride. Depending on the parent container's layout logic, DesiredSize might be fully respected, constraints on DesiredSize might be applied, and such constraints might also change other characteristics of either the parent element or child element. For example, a control that supports scrollable regions (but chooses not to derive from the 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 be ignored and the element always gets a layout that is sized by other considerations such as checking attached property values.

DesiredSize won't contain a useful value unless at least one "Measure" pass of layout has run on the element.

DesiredSize is really only intended for use when you define your own layout override methods. If you're just interested in the size of an element in your app's UI at run time, then you should use the ActualWidth and ActualHeight properties instead. You might be checking size this way if an element is influenced by dynamic layout techniques such as star sizing of Grid cells. Rely on ActualWidth and ActualHeight values only in situations that are sure to be after layout has run: for example, in Loaded events, or triggered by user actions that are only possible after the UI has been rendered initially.

Applies to

See also