How can I get the x:Name attribute of a ResourceDictionary in code behind?

As the title says, I just want to get the x:Name attribute of a ResourceDictionary in code behind.

My ResourceDictionary:

<ResourceDictionary x:Name="DefaultLight"
                    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
...
</ResourceDictionary>

My App.Xaml

<Application x:Class="WpfApp1.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfApp1"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/MyLib;component/Resources/OutgoingResources.xaml"/>
                <ResourceDictionary Source="/MyLib;component/Resources/Themes/DefaultDark.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

My code behind:

Console.WriteLine(Application.Current.Resources.MergedDictionaries[1].???);

I don't think you're going to get the name back out once it's merged.

You can, however, find the source of a resource dictionary:

        var mergedDict = Application.Current.Resources.MergedDictionaries;
        foreach (var rd in mergedDict)
        {
            Debug.WriteLine(rd.Source.OriginalString);
        }

For:

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary  Source="/Resources/Dictionary1.xaml"/>
            <ResourceDictionary  Source="/Resources/Dictionary2.xaml"/>
         </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

I get

/Resources/Dictionary1.xaml
/Resources/Dictionary2.xaml

Rather than Dictionary1 or 2 you can of course name those files DefaultLight.xaml, DefaultDark.xaml etc.

If your purpose is just to see which theme resource dictionary is merged then you could "just" have a key in each of them which tells you.

 <clr:String x:Key="CurrentTheme">DefaultDark</clr:String>

And of course DefaultLight in the light resource dictionary, with the same key.

If you wanted to have some sort of friendly name for a bunch of resource dictionaries. You could define a list allows you to decouple.
A class with name, url and IsLoaded bool in a list. Load whichever you choose in code and mark it as loaded.

There is no Name property of a ResourceDictionary that is set by the XAML processor.

You could create a custom type though that adds a Name property though:

public class NamedResourceDictionary : ResourceDictionary 
{
    public string Name { get; set; }
}

And then set the property in the XAML markup:

<ResourceDictionary>
    <ResourceDictionary.MergedDictionaries>
        <local:NamedResourceDictionary Name="Dark" Source="/MyLib;component/Resources/Themes/DefaultDark.xaml"/>
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

...and retrieve it by casting the merged resource dictionary to your custom type:

var name = (Application.Current.Resources.MergedDictionaries[0] as NamedResourceDictionary)?.Name;