What is the best pattern for building a custom control?

[ghost1372]

Currently I am creating the custom control like this:

public partial class Test : Control { }

<Style TargetType="local:Test"/>

but i see some other patterns like:

public partial class Test : Control 
{
    public Test()
    {
       this.DefaultStyleKey = typeof(Test);
     }
}

and

<Style TargetType="local:Test" BasedOn="{StaticResource DefaultTestStyle}"/>
<Style TargetType="local:Test" x:Key="DefaultTestStyle"/>

I would be grateful if someone could guide me.
Creating a DefaultXStyle makes sense because you can create other controls based on it.

But I'm not sure exactly what this.DefaultStyleKey does. Do we really need to create it? What's the problem if it doesn't exist?

[kmgallahan]

But I'm not sure exactly what this.DefaultStyleKey does. Do we really need to create it? What's the problem if it doesn't exist?

https://learn.microsoft.com/en-us/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.controls.control.defaultstylekey?view=windows-app-sdk-1.6