高效地根據屬性名獲取某對象的屬性值

終於開通了博客。以后，我就把自己平時學習心得發上來，mark……

我們在一些開發任務中，時常遇到一種情況，就是我們需要根據一個對象的屬性名稱，去獲取這個屬性的值，或者是設置值。

那么，我們通常想到的方法是反射，這是可行的。但是性能不高。以下，為大家介紹一種高性能的方法。

請看代碼：

    /// <summary>
    /// 動態訪問對象
    /// </summary>
    /// <typeparam name="T">要訪問的對象的數據類型</typeparam>
    public class PropertyAccess<T>
    {
        private static Func<object, string, object> _getValueDelegate;
        private static Action<object, string, object> _setValueDelegate;

        /// <summary>
        /// 獲取指定對象的指定屬性的值

        /// </summary>
        /// <param name="instance">要獲取屬性值的對象</param>
        /// <param name="memberName">要獲取的屬性的名稱</param>
        /// <returns></returns>
        public object GetValue(T instance, string memberName)
        {
            return _getValueDelegate(instance, memberName);
        }

        /// <summary>
        /// 為指定對象的指定屬性設置值。
        /// </summary>
        /// <param name="instance">要設置屬性的對象</param>
        /// <param name="memberName">要設置的屬性名</param>
        /// <param name="newValue">要設置的值</param>
        public void SetValue(T instance, string memberName, object newValue)
        {
            _setValueDelegate(instance, memberName, newValue);
        }

        /// <summary>
        /// 實例化 <see cref="PropertyAccess&lt;T&gt;"/> 類
        /// </summary>
        static PropertyAccess()
        {
            _getValueDelegate = GenerateGetValue();
            _setValueDelegate = GenerateSetValue();
        }

        /// <summary>
        /// 構建讀取值函數
        /// </summary>
        /// <returns></returns>
        private static Func<object, string, object> GenerateGetValue()
        {
            var type = typeof(T);
            var instance = Expression.Parameter(typeof(object), "instance");
            var memberName = Expression.Parameter(typeof(string), "memberName");
            var nameHash = Expression.Variable(typeof(int), "nameHash");
            var calHash = Expression.Assign(nameHash, Expression.Call(memberName, typeof(object).GetMethod("GetHashCode")));
            var cases = new List<SwitchCase>();
            foreach (var propertyInfo in type.GetProperties())
            {
                var property = Expression.Property(Expression.Convert(instance, typeof(T)), propertyInfo.Name);
                var propertyHash = Expression.Constant(propertyInfo.Name.GetHashCode(), typeof(int));

                cases.Add(Expression.SwitchCase(Expression.Convert(property, typeof(object)), propertyHash));
            }
            var switchEx = Expression.Switch(nameHash, Expression.Constant(null), cases.ToArray());
            var methodBody = Expression.Block(typeof(object), new[] { nameHash }, calHash, switchEx);

            return Expression.Lambda<Func<object, string, object>>(methodBody, instance, memberName).Compile();
        }

        /// <summary>
        /// 構建設置屬性值函數
        /// </summary>
        /// <returns></returns>
        private static Action<object, string, object> GenerateSetValue()
        {
            var type = typeof(T);
            var instance = Expression.Parameter(typeof(object), "instance");
            var memberName = Expression.Parameter(typeof(string), "memberName");
            var newValue = Expression.Parameter(typeof(object), "newValue");
            var nameHash = Expression.Variable(typeof(int), "nameHash");
            var calHash = Expression.Assign(nameHash, Expression.Call(memberName, typeof(object).GetMethod("GetHashCode")));
            var cases = new List<SwitchCase>();
            foreach (var propertyInfo in type.GetProperties())
            {
                // 屬性必須可寫
                if (!propertyInfo.CanWrite)
                {
                    continue;
                }
                var property = Expression.Property(Expression.Convert(instance, typeof(T)), propertyInfo.Name);
                var setValue = Expression.Assign(property, Expression.Convert(newValue, propertyInfo.PropertyType));
                var propertyHash = Expression.Constant(propertyInfo.Name.GetHashCode(), typeof(int));

                cases.Add(Expression.SwitchCase(Expression.Convert(setValue, typeof(object)), propertyHash));
            }
            var switchEx = Expression.Switch(nameHash, Expression.Constant(null), cases.ToArray());
            var methodBody = Expression.Block(typeof(object), new[] { nameHash }, calHash, switchEx);

            return Expression.Lambda<Action<object, string, object>>(methodBody, instance, memberName, newValue).Compile();
        }
    }

OK，不廢話，以下代碼演示如何使用。

 

PropertyAccess<MyClass> propertyAccess=new PropertyAccess<MyClass>();
MyClass some=new MyClass();
some.TestProperty="yeaicc ,你敢不敢獲取到？";
object obj=propertyAccess.GetValue(some,"TestProperty");
// obj就是你所獲取的值了。