Lind.DDD~实体属性变更追踪器的实现

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看着这个标题很复杂,大叔把它拆开说一下,实体属性-变更-追踪器,把它拆成三部分大家看起来就容易懂一些了,实体属性:领域实体里有自己的属性,属性有getter,setter块,用来返回和设置属性的内容;变更:当前属性为赋值时,我们对它进行监视;追踪器:对变量的内容进行处理。好了,我们回到Lind.DDD框架中,在框架里有领域实体基类EntityBase,这个类是所有实体的基类,它公开了一些属性和方法,我们对这个基类进行一些设置,让所有子类都继承它,享用它。

1 属性变更追踪接口和它的事件

    // 摘要:
    //     向客户端发出某一属性值已更改的通知。
    public interface INotifyPropertyChanged
    {
        // 摘要:
        //     在更改属性值时发生。
        event PropertyChangedEventHandler PropertyChanged;
    }

2 基类EntityBase,添加了事件和它的方法,及触发事件的方法

    /// <summary>
    /// 领域模型,实体模型基类,它可能有多种持久化方式,如DB,File,Redis,Mongodb,XML等
    /// Lind.DDD框架的领域模型与数据库实体合二为一
    /// </summary>
    [PropertyChangedAttribute]
    public abstract class EntityBase : ContextBoundObject, IEntity, INotifyPropertyChanged
    {
        /// <summary>
        /// 实体初始化
        /// </summary>
        public EntityBase()
        {
            this.Status = Status.Normal;
            this.UpdateDateTime = DateTime.Now;
            this.CreateDateTime = DateTime.Now;
            this.PropertyChanged += EntityBase_PropertyChanged;
        }

        /// <summary>
        /// 建立时间
        /// </summary>
        [XmlIgnore, DataMember(Order = 3), XmlElement(Order = 3), DisplayName("建立时间"), Column("CreateTime"), Required]
        public DateTime CreateDateTime { get; set; }
        /// <summary>
        /// 更新时间
        /// </summary>
        [XmlIgnore, DataMember(Order = 2), XmlElement(Order = 2), DisplayName("更新时间"), Column("UpdateTime"), Required]
        public DateTime UpdateDateTime { get; set; }
        /// <summary>
        /// 实体状态
        /// </summary>
        [XmlIgnore, DataMember(Order = 1), XmlElement(Order = 1), DisplayName("状态"), Required]
        public Status Status { get; set; }

        /// <summary>
        /// 拿到实体验证的结果列表
        /// 结果为null或者Enumerable.Count()==0表达验证成功
        /// </summary>
        /// <returns></returns>
        public IEnumerable<RuleViolation> GetRuleViolations()
        {
            var properties = this.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance).ToArray();

            foreach (var i in properties)
            {
                var attr = i.GetCustomAttributes();
                foreach (var a in attr)
                {
                    var val = (a as ValidationAttribute);
                    if (val != null)
                        if (!val.IsValid(i.GetValue(this)))
                        {
                            yield return new RuleViolation(val.ErrorMessage, i.Name);
                        }
                }
            }

        }

        #region PropertyChangedEventHandler Events
        /// <summary>
        /// 属性值变更事件
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;
        /// <summary>
        /// 事件实例
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void EntityBase_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            Console.WriteLine("属性:{0},值:{1}", e.PropertyName, sender.GetType().GetProperty(e.PropertyName).GetValue(sender));
        }
        /// <summary>
        /// 触发事件,写在每个属性的set块中CallerMemberName特性表示当前块的属性名
        /// </summary>
        /// <param name="propertyName"></param>
        public void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        #endregion

    }

3 定义变更拦截器特性

    /// <summary>
    /// 类中方法拦截的特性
    /// </summary>
    public class PropertyChangedAttribute : ProxyAttribute
    {
        public override MarshalByRefObject CreateInstance(Type serverType)
        {
            PropertyChangedProxy realProxy = new PropertyChangedProxy(serverType);
            return realProxy.GetTransparentProxy() as MarshalByRefObject;
        }
    }

4 实现拦截器功能

    /// <summary>
    /// 属性变更拦截器
    /// </summary>
    public class PropertyChangedProxy : RealProxy
    {
        Type serverType;
        public PropertyChangedProxy(Type serverType)
            : base(serverType)
        {
            this.serverType = serverType;
        }
        public override IMessage Invoke(IMessage msg)
        {
            //构造方法
            if (msg is IConstructionCallMessage)
            {
                IConstructionCallMessage constructCallMsg = msg as IConstructionCallMessage;
                IConstructionReturnMessage constructionReturnMessage = this.InitializeServerObject((IConstructionCallMessage)msg);
                RealProxy.SetStubData(this, constructionReturnMessage.ReturnValue);
                return constructionReturnMessage;
            }
            //其它方法(属性也是方法,它会被翻译成set_property,get_property,类似于java里的属性封装)
            else if (msg is IMethodCallMessage)
            {

                IMethodCallMessage callMsg = msg as IMethodCallMessage;
                object[] args = callMsg.Args;
                IMessage message;
                try
                {

                    if (callMsg.MethodName.StartsWith("set_") && args.Length == 1)
                    {
                        string propertyName = Regex.Split(callMsg.MethodName, "set_")[1];
                        //这里检测到是set方法,然后应怎么调用对象的其它方法呢?
                        var method = this.serverType.GetMethod("OnPropertyChanged");
                        if (method != null)
                        {
                            var obj = GetUnwrappedServer();
                            obj.GetType().GetProperty(propertyName).SetValue(obj, args.FirstOrDefault());
                            method.Invoke(obj, new object[] { propertyName });//这块对象为空了
                        }

                    }

                    object o = callMsg.MethodBase.Invoke(GetUnwrappedServer(), args);
                    message = new ReturnMessage(o, args, args.Length, callMsg.LogicalCallContext, callMsg);
                }

                catch (Exception e)
                {

                    message = new ReturnMessage(e, callMsg);

                }

                return message;

            }

            return msg;

        }
    }

5 总结

本例子主要让大家了解了事件,事件触发机制,AOP拦截技术等知识点,而且通过本例子,我们可以对类的属性进行监视,并订阅一些方法来处理这些变更行为!下面这个代码是最简单的属性变更的记录,本user对象为赋值时,它的两个被set的属性成为了监视的对象

     User u1 = new User();
     u1.UserName = "OK";
     u1.Age = 100;

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posted @ 2015-12-07 14:19  张占岭  阅读(...)  评论(...编辑  收藏