C#学习：表达式树

通过表达式树拼装lambda表达式，从而实现把一个类型的字段和属性的值复制到另外一个类型中去。

一、下面的方法实现两个类型间复制

    /// <summary>  
    /// 交换两个类型的属性（复制）  
    /// </summary>  
    /// <typeparam name="Tin"></typeparam>  
    /// <typeparam name="Tout"></typeparam>  
    public static class ExpressionCopy<Tin, Tout>  
    {  
        public static Tout Excharnge(Tin tin)  
        {  
            ParameterExpression experssionin = Expression.Parameter(typeof(Tin), "tModel");//创建实例  
            List<MemberBinding> memberList = new List<MemberBinding>();//绑定用的  
            foreach (var item in typeof(Tout).GetFields())
            {  
                FieldInfo field = typeof(Tin).GetField(item.Name.GetPropertyRemark(typeof(Tout), 1));  
                if (field != null)  
                {  
                    MemberExpression member = Expression.Field(experssionin, field);  
                    MemberBinding binding = Expression.Bind(item, member);  
                    memberList.Add(binding);  
                }  
            }  
    
            foreach (var item in typeof(Tout).GetProperties())
            {  
                PropertyInfo pro = typeof(Tin).GetProperty(item.Name.GetPropertyRemark(typeof(Tout), 2));
                if (pro != null)  
                {  
                    MemberExpression proper = Expression.Property(experssionin, pro);  
                    MemberBinding binding = Expression.Bind(item, proper);  
                    memberList.Add(binding);  
                }  
    
            }  
    
            MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(Tout)), memberList.ToArray());//初始化绑定新成员  
            Expression<Func<Tin, Tout>> lambda = Expression.Lambda<Func<Tin, Tout>>(init, new ParameterExpression[]  
            {   
            experssionin  
            });  
            return lambda.Compile().Invoke(tin);  
        }  
    }  

二、声明特性为了防止当要复制的属性字段名称不一致

/// <summary>  
    /// 特性  
    /// </summary>  
    public class GetRemarkAttribute : Attribute  
    {  
        public GetRemarkAttribute(string name)  
        {  
            this._remark = name;  
        }  
        private string _remark;  
        public string GetRemark()  
        {  
            return _remark;  
        }  
    }  

三、通过反射为string类型添加一个扩展方法，来获取特性的值

public static class GetRemark  
   {  
       /// <summary>  
       /// 通过反射获得特性  
       /// </summary>  
       /// <param name="values">字段属性名称</param>  
       /// <param name="type">类型</param>  
       /// <param name="parameter">参数1为字段2为属性</param>  
       /// <returns></returns>  
       public static string GetPropertyRemark(this string values, Type type, int parameter)  
       {  
           if (parameter == 1)  
           {  
               FieldInfo propperty = type.GetField(values);  
    
               if (propperty.IsDefined(typeof(GetRemarkAttribute)))  
               {  
                   GetRemarkAttribute remark = (GetRemarkAttribute)propperty.GetCustomAttribute(typeof(GetRemarkAttribute));  
                   return remark.GetRemark();  
               }  
    
           }  
           else  
           {  
               PropertyInfo propperty = type.GetProperty(values);  
    
               if (propperty.IsDefined(typeof(GetRemarkAttribute)))  
               {  
                   GetRemarkAttribute remark = (GetRemarkAttribute)propperty.GetCustomAttribute(typeof(GetRemarkAttribute));  
                   return remark.GetRemark();  
               }  
    
           }  
           return values;  
    
       }  
   }  

四、下面就是实际操作调用

public class OldPersoninfo  
    {  
        public int Id { get; set; }  
        public string Name { get; set; }  
        public string Type { get; set; }  
        public OldPersoninfo()  
        {  
            Id = 2;  
            Name = "测试";  
            Type = "非常类额";  
        }  
    }  
    public class NewPersoninfo  
    {  
        public int Id { get; set; }  
       // [GetRemark("Name")]  
        public string newName { get; set; }  
        //[GetRemark("Type")]  
        public string newType { get; set; }  
    }  
 

private void test_Load(object sender, EventArgs e)  
       {  
           OldPersoninfo old = new OldPersoninfo();  
           NewPersoninfo newPersoninfo = ExpressionCopy<OldPersoninfo, NewPersoninfo>.Excharnge(old);  
           MessageBox.Show(newPersoninfo.newType);  
       }