Get value for Style from property of the instance to be styled

Question

I would like to create elements during runtime and add a style to them.

Given the following Xaml, I would like to bind the value for the property Center to the actual values of a styled object (see main method). I tried different Binding notations but without success (propably because I am still new to xaml). I also tried to just change the Center on the instance but the instance is frozen and cannot be changed.

<Window x:Name="window" x:Class="CirclePing.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Style x:Key="AlertBubble" TargetType="{x:Type Path}">
            <Setter Property="StrokeThickness" Value="0"/>
            <Setter Property="Data">
                <Setter.Value>

                    <!-- how can I bind Center to the Tag property of a 'styled' instance? -->
                    <EllipseGeometry x:Name="circle"
                                Center="200,200" 
                                RadiusX="100" 
                                RadiusY="100">
                    </EllipseGeometry>

                </Setter.Value>
            </Setter>
            <Setter Property="Fill">
                <Setter.Value>
                    <RadialGradientBrush>
                        <GradientStop Color="Black"/>
                        <GradientStop Color="#2F5CB2"/>
                    </RadialGradientBrush>
                </Setter.Value>
            </Setter>
            <Setter Property="OpacityMask">
                <Setter.Value>
                    <RadialGradientBrush>
                        <GradientStop Color="#00000000" Offset="0.5"/>
                        <GradientStop Color="#FFFFFFFF" Offset="1"/>
                    </RadialGradientBrush>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
</Window>

My Main method:

    InitializeComponent();

    Random r = new Random();
    for (int i = 0; i < 500; i++)
    {
        var path = new Path();

        int positionX = r.Next(1400);
        int positionY = r.Next(800);
        path.Tag = new Point(positionX, positionY);

        path.Style = (Style)this.Resources["AlertBubble"]; 
     }

Now I would like the following to be true: (EllipseGeometry)path.Data).Center.Y == positionY . What binding expression should I use?

Answer 1

You can bind Center using RelativeSource markup extension and finding parent Path instance object like this:

<EllipseGeometry x:Name="circle"
                 Center="{Binding Tag, RelativeSource={RelativeSource 
                                       Mode=FindAncestor, AncestorType=Path}}" 
                 RadiusX="100" 
                 RadiusY="100"/>