dozob

Choose the right base class

Override the Default Style

static MyCustomControl()
{
    DefaultStyleKeyProperty.OverrideMetadata(
        typeof(MyCustomControl),
        new FrameworkPropertyMetadata(typeof(MyCustomControl));
}

Create a default Style

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    xmlns:sd="clr-namespace:System.Drawing;assembly=System.Drawing"
    xmlns:swm="clr-namespace:System.Windows.Media;assembly=PresentationCore">
 
    <Style TargetType="{x:Type local:MyCustomControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:MyCustomControl}">
                    ...
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
 
</ResourceDictionary>

public static readonly DependencyProperty MyContentProperty =
    DependencyProperty.Register(
        nameof(MyContent),
        typeof(object),
        typeof(MyCustomControl),
        new FrameworkPropertyMetadata(
            null,
            FrameworkPropertyMetadataOptions.AffectsRender |
            FrameworkPropertyMetadataOptions.AffectsParentMeasure));
 
public object MyContent
{
    get => GetValue(MyContentProperty);
    set => SetValue(MyContentProperty, value);
}