#1,175 – Custom Panel, part VII (Using Attached Property to Arrange)

Here’s an example of a custom panel that uses an attached property (weight) in determining both size and position of child elements.

    public class WeightedPanel : Panel
    {
        private static FrameworkPropertyMetadata weightMetadata =
            new FrameworkPropertyMetadata(1.0,
                FrameworkPropertyMetadataOptions.AffectsParentArrange);

        public static readonly DependencyProperty WeightProperty =
            DependencyProperty.RegisterAttached("Weight", typeof(double),
                typeof(WeightedPanel), weightMetadata);

        public static void SetWeight(DependencyObject depObj, double value)
        {
            depObj.SetValue(WeightProperty, value);
        }

        protected override Size MeasureOverride(Size availableSize)
        {
            double totalWeight = totalChildWeight();

            foreach (UIElement elem in InternalChildren)
            {
                double childWeight = (double)elem.GetValue(WeightProperty);
                double childHeight = (childWeight / totalWeight) * availableSize.Height;
                elem.Measure(new Size(availableSize.Width, childHeight));
            }

            return availableSize;
        }

        protected override Size ArrangeOverride(Size finalSize)
        {
            double totalWeight = totalChildWeight();
            double top = 0.0;

            foreach (UIElement elem in InternalChildren)
            {
                double childWeight = (double)elem.GetValue(WeightProperty);
                double childHeight = (childWeight / totalWeight) * finalSize.Height;
                Rect r = new Rect(new Point(0.0, top),
                                  new Size(elem.DesiredSize.Width, childHeight));

                elem.Arrange(r);

                top += childHeight;
            }

            return finalSize;
        }

        private double totalChildWeight()
        {
            double weightSum = 0;
            foreach (UIElement elem in InternalChildren)
                weightSum += (double)elem.GetValue(WeightProperty);

            return weightSum;
        }
    }

Below, we use this panel, specifying that 2nd label is 2x bigger (more weight) than the first label.

    <loc:WeightedPanel>
        <Label Content="I'm child #1" loc:WeightedPanel.Weight="1"
               Background="Thistle" />
        <Label Content="I'm child #2" loc:WeightedPanel.Weight="2"
               Background="Lavender" />
        <!-- Weight defaults to 1 -->
        <Label Content="Third kid"
               Background="Honeydew" />
    </loc:WeightedPanel>

1175-001

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.

One Response to #1,175 – Custom Panel, part VII (Using Attached Property to Arrange)

  1. Pingback: Dew Drop – October 8, 2014 (#1872) | Morning Dew

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