I'm trying to learn the basics of creating a custom panel in a WinRT XAML app. I have defined an attached dependency property and it's working as expected except i can't figure out how to get the property's callback for a child element to trigger the arrange or measure of the container.
What's the proper way to for a child to let it's container know that arrange and measure should be called again? In my WPF 4 unleashed book they use the FrameworkPropertyMetadataOptions.AffectsParentArrange but that doesn't seem to be available in WinRT.
public class SimpleCanvas : Panel
{
#region Variables
#region Left Property
public static double GetLeft(UIElement element)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
object value = element.GetValue(LeftProperty);
Type valueType = value.GetType();
return Convert.ToDouble(value);
}
public static void SetLeft(UIElement element, double value)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
element.SetValue(LeftProperty, value);
}
public static readonly DependencyProperty LeftProperty =
DependencyProperty.RegisterAttached("Left", typeof(double), typeof(SimpleCanvas),
new PropertyMetadata(0, OnLeftPropertyChanged));
public static void OnLeftPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
UIElement element = (UIElement)source;
// This doesn't cause ArrangeOverride below to be called
element.InvalidateArrange();
}
#endregion
#region Top Property
public static double GetTop(UIElement element)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
object value = element.GetValue(TopProperty);
return (value == null) ? 0 : (double)value;
}
public static void SetTop(UIElement element, double value)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
element.SetValue(TopProperty, value);
}
public static readonly DependencyProperty TopProperty =
DependencyProperty.RegisterAttached("Top", typeof(double), typeof(SimpleCanvas),
new PropertyMetadata(0, OnTopPropertyChanged));
public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
UIElement element = (UIElement)source;
// This doesn't cause ArrangeOverride below to be called
element.InvalidateArrange();
}
#endregion
#endregion
public SimpleCanvas()
{
}
#region Methods
protected override Size MeasureOverride(Size availableSize)
{
foreach (UIElement child in this.Children)
{
child.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
}
return new Size(0, 0);
}
protected override Size ArrangeOverride(Size finalSize)
{
foreach (UIElement child in this.Children)
{
double x = 0;
double y = 0;
double left = GetLeft(child);
double top = GetTop(child);
if (!double.IsNaN(left))
{
x = left;
}
if (!double.IsNaN(top))
{
y = top;
}
child.Arrange(new Rect(new Point(x, y), child.DesiredSize));
}
return finalSize;
}
#endregion
}
I'm late to the party, but I went the same direction and faced the same issue. Here is my solution.
In your callback you call InvalidateArrange on the child element you attached you property to:
public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
UIElement element = (UIElement)source;
// This doesn't cause ArrangeOverride below to be called
element.InvalidateArrange();
}
But you should really invalidate the panel, by changing you code so:
public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
UIElement panel= VisualTreeHelper.GetParent(source) as UIElement;
if(panel != null)
panel.InvalidateArrange();
}
And it should work (did for me).
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