Add property changed callback with virtual instance method

[JohanLarsson]

Default hidden, for convenience.
Before:

namespace RoslynSandbox
{
    using System.Windows;
    using System.Windows.Controls;

    public class FooControl : Control
    {
        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
            nameof(Value),
            typeof(double),
            typeof(FooControl),
            new PropertyMetadata(default(double)));

        public double Value
        {
            get => (double)this.GetValue(ValueProperty);
            set => this.SetValue(ValueProperty, value);
        }
    }
}

After:

namespace RoslynSandbox
{
    using System.Windows;
    using System.Windows.Controls;

    public class FooControl : Control
    {
        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
            nameof(Value),
            typeof(double),
            typeof(FooControl),
            new PropertyMetadata(
                default(double),
                (d, e) => ((FooControl)d).OnValueChanged((double)e.OldValue, (double)e.NewValue)));

        public double Value
        {
            get => (double)this.GetValue(ValueProperty);
            set => this.SetValue(ValueProperty, value);
        }

        /// <summary>
        /// This method is invoked when <see cref="ValueProperty"/> changes value.
        /// </summary>
        /// <param name="oldValue">The old value of <see cref="ValueProperty"/>.</param>
        /// <param name="newValue">The new value of <see cref="ValueProperty"/>.</param>
        protected virtual void OnValueChanged(double oldValue, double newValue)
        {
        }
    }
}

[JohanLarsson]

Maybe better as a refactoring.

[JohanLarsson]

Refactorings via nuget will work in some future VS version.