#1,172 – Custom Panel, part IV (ZIndex)

By default, a Panel control will respect its children elements’ Panel.ZIndex values when doing layout.  In the custom panel below, we overlap child elements during the arrange phase.

    public class MyPanel : Panel
        protected override Size MeasureOverride(Size availableSize)
            Size childSize = new Size(availableSize.Width, double.PositiveInfinity);

            foreach (UIElement elem in InternalChildren)

            return availableSize;

        protected override Size ArrangeOverride(Size finalSize)
            Size childSize;

            double top = 0.0;
            for (int i = 0; i < InternalChildren.Count; i++)
                childSize = new Size(finalSize.Width, InternalChildren[i].DesiredSize.Height);
                Rect r = new Rect(new Point(0.0, top), childSize);
                top += childSize.Height * 0.5;

            return finalSize;

If we don’t specify ZIndex values, each child layers on top of the previous child.
We can reverse the order by specifying explicit ZIndex values:

    <loc:MyPanel Margin="5" Background="LightGray">
        <Label Content="I'm child #1" Panel.ZIndex="3"
               Background="Thistle" />
        <Label Content="I'm child #2" Panel.ZIndex="2"
               Background="Lavender" />
        <Label Content="Third kid"  Panel.ZIndex="1"
               Background="Honeydew" />


About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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