Property event to observable.

Observable.cs

class Observable
{
    private object actionCollection = null!;
    private MethodInfo? methodInfo;

    public ActionCollection<TModel> From<TModel>(TModel target) where TModel : INotifyPropertyChanged
    {
        RegisterPropertyChanged(target);
        return BuildActionCollection<TModel>();
    }

    private void RegisterPropertyChanged<TModel>(TModel target) where TModel : INotifyPropertyChanged
    {
        target.PropertyChanged -= Model_PropertyChanged;
        target.PropertyChanged += Model_PropertyChanged;
    }

    private ActionCollection<TModel> BuildActionCollection<TModel>() where TModel : notnull
    {
        var type = typeof(ActionCollection<TModel>);
        methodInfo = type.GetMethod(nameof(ActionCollection<TModel>.Get));
        actionCollection = new ActionCollection<TModel>();
        return (ActionCollection<TModel>)actionCollection;
    }

    private void Model_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        var actionList = GetActionList();
        if (!actionList.ContainsKey(e.PropertyName))
            return;
        
        var type = sender.GetType();
        var property = type.GetProperty(e.PropertyName);
        var value = property.GetValue(sender, null);
        var action = actionList[e.PropertyName];
        action(value);
    }

    private IReadOnlyDictionary<string, Action<object>> GetActionList()
    {
        var returnValue = methodInfo!.Invoke(actionCollection, null);
        return (IReadOnlyDictionary<string, Action<object>>)returnValue;
    }

    public class ActionCollection<TModel> where TModel : notnull
    {
        private readonly Dictionary<string, Action<object>> actionList = new();

        public ActionCollection<TModel> On<TProperty>(Expression<Func<TModel, TProperty>> expression, Action<TProperty> action)
        {
            var propertyName = expression.GetMemberName();
            actionList[propertyName] = (param) => action((TProperty)param);
            return this;
        }

        public IReadOnlyDictionary<string, Action<object>> Get() => actionList;
    }
}