Prism 订阅事件 IEventAggregator 说明

//定义CompositePresentationEvent<TPayload>类
    //（1）该类是泛型类:强制发布者和订阅者要一种正确的类型实现 发布-订阅连接
    //（2）是唯一继承自EventBase的类
    //(3)因为CompositePresentationEvent<TPayload>往往被多个模块公用，所以要单独于
    //   其他的模块新建类库项目
    //FundOrder是这里的TPayLoad类型
    public class FundAddedEvent : CompositePresentationEvent<FundOrder>
    {
    }

public class AddFundPresenter
    {
        private IAddFundView _view;
        //IEventAggregator 事件聚合器接口
        private IEventAggregator eventAggregator;

        public AddFundPresenter(IEventAggregator eventAggregator)
        {
            this.eventAggregator = eventAggregator;
        }

        //事件发布：当用户添加一个fund基金，事件就被发布
        //发布者发布一个事件
        //(1)通过IEventAggregator的实例eventAggregator的Publish方法
        //(2)指定GetEvent<TEventType>中TEventType为FunAddedEvent
        void AddFund(object sender, EventArgs e)
        {
            FundOrder fundOrder = new FundOrder();
            fundOrder.CustomerId = View.Customer;
            fundOrder.TickerSymbol = View.Fund;

            if (!string.IsNullOrEmpty(fundOrder.CustomerId) && !string.IsNullOrEmpty(fundOrder.TickerSymbol))
                eventAggregator.GetEvent<FundAddedEvent>().Publish(fundOrder);
        }

        public IAddFundView View
        {
            get { return _view; }
            set
            {
                _view = value;
                _view.AddFund += AddFund;
            }
        }

    }

public class ActivityPresenter
    {
        private string _customerId;
        private IEventAggregator eventAggregator;
        private SubscriptionToken subscriptionToken;

        public ActivityPresenter(IEventAggregator eventAggregator)
        {
            this.eventAggregator = eventAggregator;
        }

        public void FundAddedEventHandler(FundOrder fundOrder)
        {
            Debug.Assert(View != null);
            View.AddContent(fundOrder.TickerSymbol);
        }

        public bool FundOrderFilter(FundOrder fundOrder)
        {
            return fundOrder.CustomerId == _customerId;
        }

        public IActivityView View { get; set; }

        public string CustomerId
        {
            get
            {
                return _customerId;
            }

            set
            {
                _customerId = value;

                FundAddedEvent fundAddedEvent = eventAggregator.GetEvent<FundAddedEvent>();

                if (subscriptionToken != null)
                {
                    fundAddedEvent.Unsubscribe(subscriptionToken);
                }
                //订阅事件
                //(1)获取事件聚合器实例
                //(2)调用Subscribe方法
                //   Subscribe方法重载，有不同的作用
                //            Action<T>: 泛型委托
                //            ThreadOption:当为PublisherThread时（默认值）能获取发布者线程
                //                          BackgroundThread时 从.NET Framework线程池上异步获取事件
                //                          UIThread时 获取事件从UI线程上。    
                //             keepSubscriberReferenceAlive: 当为true 事件实例是强引用订阅者，因此不能垃圾回收 
                //                                           当为false（默认值）弱引用订阅者，因此当没有其他引用时允许垃圾回收释放订阅者实例，当订阅者实例被回收，事件自动取消订阅
                subscriptionToken = fundAddedEvent.Subscribe(FundAddedEventHandler, ThreadOption.UIThread, false, FundOrderFilter);
                //lamda表达式写法
                //subscriptionToken = fundAddedEvent.Subscribe(FundAddedEventHandler, ThreadOption.UIThread, false, FunOrder => FunOrder.CustomerId == this._customerId);
                View.SetTitle(string.Format(CultureInfo.CurrentCulture, Resources.ActivityTitle, CustomerId));
            }
        }
    }