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;
