The following WPF UserControl called DataTypeWholeNumber which works.
Now I want to make a UserControl called DataTypeDateTime and DataTypeEmail, etc.
Many of the Dependency Properties will be shared by all these controls and therefore I want to put their common methods into a BaseDataType and have each of these UserControls inherit from this base type.
However, when I do that, I get the error: Partial Declaration may not have different base classes.
So how can I implement inheritance with UserControls so shared functionality is all in the base class?
using System.Windows;
using System.Windows.Controls;
namespace TestDependencyProperty827.DataTypes
{
    public partial class DataTypeWholeNumber : BaseDataType
    {
        public DataTypeWholeNumber()
        {
            InitializeComponent();
            DataContext = this;
            //defaults
            TheWidth = 200;
        }
        public string TheLabel
        {
            get
            {
                return (string)GetValue(TheLabelProperty);
            }
            set
            {
                SetValue(TheLabelProperty, value);
            }
        }
        public static readonly DependencyProperty TheLabelProperty =
            DependencyProperty.Register("TheLabel", typeof(string), typeof(BaseDataType),
            new FrameworkPropertyMetadata());
        public string TheContent
        {
            get
            {
                return (string)GetValue(TheContentProperty);
            }
            set
            {
                SetValue(TheContentProperty, value);
            }
        }
        public static readonly DependencyProperty TheContentProperty =
            DependencyProperty.Register("TheContent", typeof(string), typeof(BaseDataType),
            new FrameworkPropertyMetadata());
        public int TheWidth
        {
            get
            {
                return (int)GetValue(TheWidthProperty);
            }
            set
            {
                SetValue(TheWidthProperty, value);
            }
        }
        public static readonly DependencyProperty TheWidthProperty =
            DependencyProperty.Register("TheWidth", typeof(int), typeof(DataTypeWholeNumber),
            new FrameworkPropertyMetadata());
    }
}