DependencyPropertyHelper.cs

public delegate void PropertyChangedCallback<T>(T sender, DependencyPropertyChangedEventArgs e) where T : DependencyObject;

public static class DependencyPropertyHelper
{
    public static DependencyProperty Register<TProperty, TOwner>(string name,
        TProperty defaultValue = default(TProperty),
        PropertyChangedCallback<TOwner> callback = null) where TOwner : DependencyObject
    {
        return RegisterImpl(false, name, defaultValue, callback);
    }

    public static DependencyProperty RegisterAttached<TProperty, TOwner>(string name,
        TProperty defaultValue = default(TProperty),
        PropertyChangedCallback<TOwner> callback = null) where TOwner : DependencyObject
    {
        return RegisterImpl(true, name, defaultValue, callback);
    }

    private static DependencyProperty RegisterImpl<TProperty, TOwner>(bool isAttached,
        string name,
        TProperty defaultValue = default(TProperty),
        PropertyChangedCallback<TOwner> callback = null) where TOwner : DependencyObject
    {
        var callbackWrapper = callback != null
            ? (sender, e) => callback((TOwner) sender, e)
            : (PropertyChangedCallback) null;

        return isAttached
            ? DependencyProperty.RegisterAttached(name,
                typeof (TProperty),
                typeof (TOwner),
                new PropertyMetadata(defaultValue, callbackWrapper))
            : DependencyProperty.Register(name,
                typeof (TProperty),
                typeof (TOwner),
                new PropertyMetadata(defaultValue, callbackWrapper));
    }
}