常用方法 反射常见方法

 　　　　/// <summary>
        /// DataTable 转换为 对象List
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="dt"></param>
        /// <returns></returns>
        public static List<T> DataTableToEntities<T>(this DataTable dt) where T : class, new()
        {
            if (null == dt || dt.Rows.Count == 0) { return null; }
            List<T> entities = new List<T>();

            foreach (DataRow row in dt.Rows)
            {
                PropertyInfo[] pArray = typeof(T).GetProperties();
                T entity = new T();

                Array.ForEach<PropertyInfo>(pArray, p =>
                {
                    object cellvalue = row[p.Name];
                    if (cellvalue != DBNull.Value)
                    {
                        //经过了几个版本的迭代，最后一个为最新的，摘自网上，已附原文地址


                        //4、原地址：https://blog.csdn.net/Simon1003/article/details/80839744
                        if (!p.PropertyType.IsGenericType)
                        {
                            p.SetValue(entity, Convert.ChangeType(cellvalue, p.PropertyType), null);
                        }
                        else
                        {
                            Type genericTypeDefinition = p.PropertyType.GetGenericTypeDefinition();
                            if (genericTypeDefinition == typeof(Nullable<>))
                            {
                                p.SetValue(entity, Convert.ChangeType(cellvalue, Nullable.GetUnderlyingType(p.PropertyType)), null);
                            }
                            else
                            {
                                throw new Exception("genericTypeDefinition != typeof(Nullable<>)");
                            }
                        }


                        //3、原地址：https://blog.csdn.net/hebbers/article/details/78957569
                        //Type type = p.PropertyType;
                        //if (type.IsGenericType && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))//判断convertsionType是否为nullable泛型类  
                        //{
                        //    //如果type为nullable类，声明一个NullableConverter类，该类提供从Nullable类到基础基元类型的转换
                        //    System.ComponentModel.NullableConverter nullableConverter = new System.ComponentModel.NullableConverter(type);
                        //    //将type转换为nullable对的基础基元类型
                        //    type = nullableConverter.UnderlyingType;
                        //}
                        //p.SetValue(entity, Convert.ChangeType(cellvalue, type), null);


                        //2、自定义 这种很傻，但当前解决速度最快
                        //if (p.PropertyType.Name.Equals("Int32"))
                        //{
                        //    p.SetValue(entity, Convert.ToInt32(value), null);
                        //}
                        //else if (p.PropertyType.Name.Equals("String"))
                        //{
                        //    p.SetValue(entity, Convert.ToString(value), null);
                        //}
                        //else if (p.PropertyType.Name.Equals("Nullable`1"))
                        //{
                        //    p.SetValue(entity, Convert.ToInt32(value), null);
                        //}
                        ////其它类型 暂时不管 


                        //1、字段不为空可以用这种
                        //p.SetValue(entity, value, null);
                    }
                });
                entities.Add(entity);
            }
            return entities;
        }

        public static List<T> DataTableToEntities2<T>(this DataTable dt) where T : class, new()
        {
            if (null == dt || dt.Rows.Count == 0) { return null; }
            List<T> entities = new List<T>();

            foreach (DataRow row in dt.Rows)
            {
                PropertyInfo[] pArray = typeof(T).GetProperties();
                T entity = new T();

                Array.ForEach<PropertyInfo>(pArray, p =>
                {
                    object cellvalue = row[p.Name];
                    if (cellvalue != DBNull.Value)
                    {
                        if (!p.PropertyType.IsGenericType)
                        {
                            p.SetValue(entity, Convert.ChangeType(cellvalue, p.PropertyType), null);
                        }
                        else
                        {
                            Type genericTypeDefinition = p.PropertyType.GetGenericTypeDefinition();
                            if (genericTypeDefinition == typeof(Nullable<>))
                            {
                                p.SetValue(entity, Convert.ChangeType(cellvalue, Nullable.GetUnderlyingType(p.PropertyType)), null);
                            }
                            else
                            {
                                throw new Exception("genericTypeDefinition != typeof(Nullable<>)");
                            }
                        }
                    }
                });
                entities.Add(entity);
            }
            return entities;
        }

        public static List<T> DataTableToEntities3<T>(DataTable dt) where T : class, new()
        {
            if (null == dt || dt.Rows.Count == 0) { return null; }
            List<T> entities = new List<T>();

            foreach (DataRow row in dt.Rows)
            {
                PropertyInfo[] pArray = typeof(T).GetProperties();
                T entity = new T();

                Array.ForEach<PropertyInfo>(pArray, p =>
                {
                    object cellvalue = row[p.Name];
                    if (cellvalue != DBNull.Value)
                    {
                        //经过了几个版本的迭代，最后一个为最新的，摘自网上，已附原文地址


                        //4、原地址：https://blog.csdn.net/Simon1003/article/details/80839744
                        if (!p.PropertyType.IsGenericType)
                        {
                            p.SetValue(entity, Convert.ChangeType(cellvalue, p.PropertyType), null);
                        }
                        else
                        {
                            Type genericTypeDefinition = p.PropertyType.GetGenericTypeDefinition();
                            if (genericTypeDefinition == typeof(Nullable<>))
                            {
                                p.SetValue(entity, Convert.ChangeType(cellvalue, Nullable.GetUnderlyingType(p.PropertyType)), null);
                            }
                            else
                            {
                                throw new Exception("genericTypeDefinition != typeof(Nullable<>)");
                            }
                        }


                        //3、原地址：https://blog.csdn.net/hebbers/article/details/78957569
                        //Type type = p.PropertyType;
                        //if (type.IsGenericType && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))//判断convertsionType是否为nullable泛型类  
                        //{
                        //    //如果type为nullable类，声明一个NullableConverter类，该类提供从Nullable类到基础基元类型的转换
                        //    System.ComponentModel.NullableConverter nullableConverter = new System.ComponentModel.NullableConverter(type);
                        //    //将type转换为nullable对的基础基元类型
                        //    type = nullableConverter.UnderlyingType;
                        //}
                        //p.SetValue(entity, Convert.ChangeType(cellvalue, type), null);


                        //2、自定义 这种很傻，但当前解决速度最快
                        //if (p.PropertyType.Name.Equals("Int32"))
                        //{
                        //    p.SetValue(entity, Convert.ToInt32(value), null);
                        //}
                        //else if (p.PropertyType.Name.Equals("String"))
                        //{
                        //    p.SetValue(entity, Convert.ToString(value), null);
                        //}
                        //else if (p.PropertyType.Name.Equals("Nullable`1"))
                        //{
                        //    p.SetValue(entity, Convert.ToInt32(value), null);
                        //}
                        ////其它类型 暂时不管 


                        //1、字段不为空可以用这种
                        //p.SetValue(entity, value, null);
                    }
                });
                entities.Add(entity);
            }
            return entities;
        }

        /// <summary>
        /// 跟属性赋值
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="model"></param>
        /// <param name="name"></param>
        /// <param name="value"></param>
        public static void AssignValueToAttribute<T>(T model, string name, object value)
        {
            Type t = model.GetType();
            var p = t.GetProperty(name);

            if (!p.PropertyType.IsGenericType)
            {
                p.SetValue(model, Convert.ChangeType(value, p.PropertyType), null);
            }
            else
            {
                Type genericTypeDefinition = p.PropertyType.GetGenericTypeDefinition();
                if (genericTypeDefinition == typeof(Nullable<>))
                {
                    p.SetValue(model, Convert.ChangeType(value, Nullable.GetUnderlyingType(p.PropertyType)), null);
                }
                else
                {
                    throw new Exception("genericTypeDefinition != typeof(Nullable<>)");
                }
            }
        }


        /// <summary>
        /// 获取属性值
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="model"></param>
        /// <param name="name"></param>
        /// <returns></returns>
        public static object GetValueByAttribute<T>(T model, string name)
        {
            Type t = model.GetType();
            var p = t.GetProperty(name);
            return p.GetValue(model, null);
        }

        /// <summary>
        /// 跟属性赋值
        /// 把一个对象的属性 赋值到 另一个对象
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="model"></param>
        /// <param name="name"></param>
        /// <param name="model_old"></param>
        public static void AssignValueToAttribute<T>(T model, string name, T model_old)
        {
            Type t = model_old.GetType();
            var p = t.GetProperty(name);
            object obj = p.GetValue(model_old, null);
            
            AssignValueToAttribute(model, name, obj);
        }