FrameworkElement.MeasureOverride Method

When overridden in a derived class, measures the size in layout required for child elements and determines a size for the FrameworkElement-derived class.

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

protected virtual Size MeasureOverride(
	Size availableSize
)

Parameters

availableSize
Type: System.Windows.Size

The available size that this element can give to child elements. Infinity can be specified as a value to indicate that the element will size to whatever content is available.

Return Value

Type: System.Windows.Size
The size that this element determines it needs during layout, based on its calculations of child element sizes.

Override MeasureOverride to implement custom layout sizing behavior for your element as it participates in the Windows Presentation Foundation (WPF) layout system. Your implementation should do the following:

  1. Iterate your element's particular collection of children that are part of layout, call Measure on each child element.

  2. Immediately get DesiredSize on the child (this is set as a property after Measure is called).

  3. Compute the net desired size of the parent based upon the measurement of the child elements.

The return value of MeasureOverride should be the element's own desired size, which then becomes the measure input for the parent element of the current element. This same process continues through the layout system until the root element of the page is reached.

During this process, child elements might return a larger DesiredSize size than the initial availableSize to indicate that the child element wants more space. This might be handled in your own implementation by introducing a scrollable region, by resizing the parent control, by establishing some manner of stacked order, or any number of solutions for measuring or arranging content.

Important noteImportant

Elements should call Measure on each child during this process, otherwise the child elements will not be correctly sized or arranged.

Notes to Inheritors

The following non-compiling code shows this implementation pattern. VisualChildren represents an enumerable collection property of children that your own element should define. The property can be named anything. VisualChildren is a placeholder name for purposes of this example, VisualChildren is not an API as provided by WPF or a part of a naming pattern..

protected override Size MeasureOverride(Size availableSize)
{
    Size desiredSize = new Size();
    foreach (UIElement child in VisualChildren)
    {
        child.Measure(availableSize);
        // do something with child.DesiredSize, either sum them directly or apply whatever logic your element has for reinterpreting the child sizes 
        // if greater than availableSize, must decide what to do and which size to return
    }
    // desiredSize = ... computed sum of children's DesiredSize ...; 
    // IMPORTANT: do not allow PositiveInfinity to be returned, that will raise an exception in the caller! 
    // PositiveInfinity might be an availableSize input; this means that the parent does not care about sizing 
    return desiredSize;
}

This example shows how to override the default layout behavior of the Panel element and create custom layout elements that are derived from Panel.

The example defines a simple custom Panel element called PlotPanel, which positions child elements according to two hard-coded x- and y-coordinates. In this example, x and y are both set to 50; therefore, all child elements are positioned at that location on the x and y axes.

To implement custom Panel behaviors, the example uses the MeasureOverride and ArrangeOverride methods. Each method returns the Size data that is necessary to position and render child elements.

public class PlotPanel : Panel
{
    // Default public constructor 
    public PlotPanel()
        : base()
    {
    }

    // Override the default Measure method of Panel 
    protected override Size MeasureOverride(Size availableSize)
    {
        Size panelDesiredSize = new Size();

        // In our example, we just have one child.  
        // Report that our panel requires just the size of its only child. 
        foreach (UIElement child in InternalChildren)
        {
            child.Measure(availableSize);
            panelDesiredSize = child.DesiredSize;
        }

        return panelDesiredSize ;
    }
    protected override Size ArrangeOverride(Size finalSize)
    {
        foreach (UIElement child in InternalChildren)
        {
            double x = 50;
            double y = 50;

            child.Arrange(new Rect(new Point(x, y), child.DesiredSize));
        }
        return finalSize; // Returns the final Arranged size
    }
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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