WPF converter implied in custom control? - wpf

Question

In my WPF Custom Control which draws a pie chart, I successfully made it draw a pie chart given a set of values in a string, for example "10 20 30" would draw a pie chart with correct proportions. I bound the DrawingImage's drawing property to a converter to convert from the string into a DrawingGroup. This worked great, but I am trying to bypass the need for a converter.
Here is my MainWindow:
<Grid Margin="10">
<local:PieChart DrawingCode="289 666 1337 780" Width="400" Height="400" RingWidth="300" Background="White" />
</Grid>
Here is my template for the custom control:
<Style TargetType="{x:Type local:PieChart}">
<Setter Property="HorizontalContentAlignment" Value="Center" />
<Setter Property="VerticalContentAlignment" Value="Center" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:PieChart}">
<Grid>
<Image Width="{TemplateBinding Width}" Height="{TemplateBinding Height}">
<Image.Source>
<DrawingImage Drawing="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=DrawingCode}" />
</Image.Source>
</Image>
<Ellipse Width="{TemplateBinding RingWidth}" Height="{TemplateBinding RingWidth}" Fill="{TemplateBinding Background}" />
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
And finally, here is my attempt at the Custom Control class:
public class PieChart : Control
{
public static readonly DependencyProperty DrawingCodeProperty = DependencyProperty.Register("DrawingCode", typeof(string), typeof(PieChart), new UIPropertyMetadata(null));
public static readonly DependencyProperty RingWidthProperty = DependencyProperty.Register("RingWidth", typeof(double), typeof(PieChart), new UIPropertyMetadata(null));
static PieChart()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(PieChart), new FrameworkPropertyMetadata(typeof(PieChart)));
}
public string DrawingCode
{
get { return DrawingCodeConverter((string)GetValue(DrawingCodeProperty)); }
set { SetValue(DrawingCodeProperty, value); }
}
public double RingWidth
{
get { return (double)GetValue(RingWidthProperty); }
set { SetValue(RingWidthProperty, this.Width - value); }
}
public DrawingGroup DrawingCodeConverter(string value)
{
// This converter works but is long so I removed it from the post.
}
}
I am pretty sure the problem is somewhere in the data types I should be using. Also, if there is a completely different way to do this that I am ignorant of, please let me know. Also note that RingWidth is not the problem, it is DrawingCode.

Answer 1

The getter and setter of the CLR wrapper of a dependency property may be bypassed when the property is accessed in XAML or by a Binding, Style Setter, Animation, etc. WPF then calls GetValue and SetValue directly. The reason is explained in XAML Loading and Dependency Properties
You must therefore not call anything else than GetValue and SetValue in the getter and setter. Instead, declare your dependency property with a PropertyChangedCallback like this:
public static readonly DependencyProperty DrawingCodeProperty =
DependencyProperty.Register(
"DrawingCode",
typeof(string),
typeof(PieChart),
new FrameworkPropertyMetadata(DrawingCodePropertyChanged));
public string DrawingCode
{
get { return (string)GetValue(DrawingCodeProperty); }
set { SetValue(DrawingCodeProperty, value); }
}
private static void DrawingCodePropertyChanged(
DependencyObject o, DependencyPropertyChangedEventArgs e)
{
var pieChart = (PieChart)o;
pieChart.SetDrawingCode((string)e.NewValue);
}
private void SetDrawingCode(string drawingCode)
{
var drawingGroup = DrawingCodeConverter(drawingCode);
// do something with drawingGroup
}