式木によるBindableBase

最近思いついた、けどきっと誰かやってると思うアイディア。

よくあるBindableBaseはこんな感じ

    public abstract class BindableBase : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
        {
            if (Equals(storage, value)) return false;

            storage = value;
            OnPropertyChanged(propertyName);

            return true;
        }
        protected void OnPropertyChanged([CallerMemberName] string propertyName = null) 
        {
            this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

問題点はプロパティはrefで使えないこと。

幸せになるためにこんなクラスを追加して(From ReactiveProperty)

    public static class AccessorCache<TType>
    {
        private static readonly Dictionary<string, Delegate> getCache = new Dictionary<string, Delegate>();
        private static readonly Dictionary<string, Delegate> setCache = new Dictionary<string, Delegate>();

        public static Func<TType, TProperty> LookupGet<TProperty>(Expression<Func<TType, TProperty>> propertySelector)
        {
            var propertyName = GetPropertyName(propertySelector);
            Delegate accessor;

            lock (getCache)
            {
                if (!getCache.TryGetValue(propertyName, out accessor))
                {
                    accessor = propertySelector.Compile();
                    getCache.Add(propertyName, accessor);
                }
            }

            return (Func<TType, TProperty>)accessor;
        }

        private static string GetPropertyName<TProperty>(Expression<Func<TType, TProperty>> propertySelector)
        {
            var memberExpression = propertySelector.Body as MemberExpression;
            if (memberExpression == null)
            {
                var unaryExpression = propertySelector.Body as UnaryExpression;
                if (unaryExpression == null) { throw new ArgumentException(nameof(propertySelector)); }
                memberExpression = unaryExpression.Operand as MemberExpression;
                if (memberExpression == null) { throw new ArgumentException(nameof(propertySelector)); }
            }

            return memberExpression.Member.Name;
        }

        public static Action<TType, TProperty> LookupSet<TProperty>(Expression<Func<TType, TProperty>> propertySelector)
        {
            var propertyName = GetPropertyName(propertySelector);
            Delegate accessor;

            lock (setCache)
            {
                if (!setCache.TryGetValue(propertyName, out accessor))
                {
                    accessor = CreateSetAccessor(propertySelector);
                    setCache.Add(propertyName, accessor);
                }
            }

            return (Action<TType, TProperty>)accessor;
        }

        private static Delegate CreateSetAccessor<TProperty>(Expression<Func<TType, TProperty>> propertySelector)
        {
            var propertyInfo = (PropertyInfo)((MemberExpression)propertySelector.Body).Member;
            var selfParameter = Expression.Parameter(typeof(TType), "self");
            var valueParameter = Expression.Parameter(typeof(TProperty), "value");
            var body = Expression.Assign(Expression.Property(selfParameter, propertyInfo), valueParameter);
            var lambda = Expression.Lambda<Action<TType, TProperty>>(body, selfParameter, valueParameter);
            return lambda.Compile();
        }
    }

こんなメソッドを作ってみる

        protected bool SetProperty<TType, TProperty>(TType targetClass, Expression<Func<TType, TProperty>> selector, TProperty value, [CallerMemberName] String propertyName = null)
        {
            var oldValue = AccessorCache<TType>.LookupGet(selector).Invoke(targetClass);

            if (object.Equals(oldValue, value)) return false;

            AccessorCache<TType>.LookupSet(selector).Invoke(targetClass, value);
            this.OnPropertyChanged(propertyName);
            return true;
        }

こんな感じに書ける

    public class Hoge : BindableBase
    {
        private readonly TextView _textView;

        public Hoge()
        {
            _textView = new TextView();
        }

        public string Text
        {
            get => _textView.Text;
            set => SetProperty(_textView, tv => tv.Text, value);
        }
    }

ちょっと幸せになれるかもしれない。