WPF DesignData not working

Question

I have a MVVM WPF application with a simple ListView. The ViewModel currently just contains a List property. I added a DesignData/SampleData.xaml file, set its Build Action to "DesignData" and referenced it in the Window's XAML code

<Window x:Class="..."
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
        xmlns:local="..."
        mc:Ignorable="d" 
        Title="MainWindow" Height="483" Width="932">

    <Grid d:DataContext="{d:DesignData Source=./DesignData/SampleData.xaml}">

But nothing shows up in the designer and VS2010 just gives me the following warning: The file './DesignData/SampleData.xaml' is not part of the project or its 'Build Action' is not set to 'Resource'.

No matter what the "Build Action" it still gives me the same warning.

SampleData.xaml:

<MainWindowViewModel xmlns="clr-namespace:..." 
                     xmlns:local="clr-namespace:...">
    <MainWindowViewModel.Orders>
        <local:Order OrderId="1000654321"/>
    </MainWindowViewModel.Orders>
</MainWindowViewModel>

Any ideas on how to fix that?

Edit:

Project structure

Answer 1

The DesignData path is wrong as I thought it was relative to the solution/project whereas it seems it is relative to the containing XAML file.