Question

I have a pie chart on a WPF user control whose data changes periodically, however I am not instantiating a new chart control each time, just clearing the data in the ItemsSource and then inserting new values.

Each time the values get refreshed, the colour palate continues rolling through its colour selections.

The chart colour selection always starts off with the same colour selections (first is red, then blue etc), I would like to be able to tell the chart to restart its colour selection from scratch each time I reset the data source, instead of getting different colours everytime I clear the and reset the data items.

I tried creating a new instance of the ObservableCollection each time but that did not make any difference.

Answer 1

I’ve got the same problem, and I found another solution. Maybe it’s not the better one, but it works.

I added an int property to my object binding on the PieSeries, who represent the element’s index in the ObservableCollection.
Then I created a ResourceDictionaryCollection which contains all the default colors of the Palette:

<datavis:ResourceDictionaryCollection x:Key="CouleursGraphique">
    <!-- Blue -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFB9D6F7" />
        <GradientStop Color="#FF284B70" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Red -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFFBB7B5" />
        <GradientStop Color="#FF702828" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Light Green -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFB8C0AC" />
        <GradientStop Color="#FF5F7143" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Yellow -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFFDE79C" />
        <GradientStop Color="#FFF6BC0C" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Indigo -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFA9A3BD" />
        <GradientStop Color="#FF382C6C" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Magenta -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFB1A1B1" />
        <GradientStop Color="#FF50224F" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Dark Green -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FF9DC2B3" />
        <GradientStop Color="#FF1D7554" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Gray Shade -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFB5B5B5" />
        <GradientStop Color="#FF4C4C4C" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Blue -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FF98C1DC" />
        <GradientStop Color="#FF0271AE" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Brown -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFC1C0AE" />
        <GradientStop Color="#FF706E41" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Cyan -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFADBDC0" />
        <GradientStop Color="#FF446A73" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Special Blue -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FF2F8CE2" />
        <GradientStop Color="#FF0C3E69" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Gray Shade 2 -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFDCDCDC" />
        <GradientStop Color="#FF757575" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Gray Shade 3 -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFF4F4F4" />
        <GradientStop Color="#FFB7B7B7" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
    <!-- Gray Shade 4 -->
    <ResourceDictionary>
      <RadialGradientBrush x:Key="Background" GradientOrigin="-0.1,-0.1" Center="0.075,0.015" RadiusX="1.05" RadiusY="0.9">
        <GradientStop Color="#FFF4F4F4" />
        <GradientStop Color="#FFA3A3A3" Offset="1" />
      </RadialGradientBrush>
    </ResourceDictionary>
  </datavis:ResourceDictionaryCollection>

I added a converter that returns the color at the specified index of ResourceDictionaryCollection.

 /// <summary>
    /// Convertit une valeur.
    /// </summary>
    /// <param name="value">Valeur produite par la source de liaison.</param>
    /// <param name="targetType">Type de la propriété de cible de liaison.</param>
    /// <param name="parameter">Paramètre de convertisseur à utiliser.</param>
    /// <param name="culture">Culture à utiliser dans le convertisseur.</param>
    /// <returns>
    /// Une valeur convertie. Si la méthode retourne null, la valeur Null valide est utilisée.
    /// </returns>
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        ResourceDictionaryCollection listeCouleurs = parameter as ResourceDictionaryCollection;
        int indice = (int)value;

        return listeCouleurs[indice % listeCouleurs.Count]["Background"];
    }

And i used all this elements in the Xaml like this:

  <charting:Chart.Series>
<charting:PieSeries ItemsSource="{Binding Path=Donnees}"
                    DependentValuePath="Valeur"
                    IndependentValuePath="Libelle">
  <charting:PieSeries.Palette>
    <datavis:ResourceDictionaryCollection>
      <ResourceDictionary>
        <Style x:Key="DataPointStyle" TargetType="Control">
          <Setter Property="Background" Value="{Binding Path=Index, Converter={StaticResource convCouleur}, ConverterParameter={StaticResource CouleursGraphique}}"/>
        </Style>
      </ResourceDictionary>
    </datavis:ResourceDictionaryCollection>
  </charting:PieSeries.Palette>
</charting:PieSeries>

I hope that answer can help you.