使用ASP.NET MVC 4 Async Action+jQuery实现消息通知机制的实现代码

这两天在使用Asp.net MVC 4开发COMET消息通知机制，在后端使用异步线程对消息进行订阅，客户端通过AJAX长连接请求MVC中的ACTION，如：，即表示获取ImageSet对象的变更消息（新增，更新和删除消息)。

1.事件消息的类IEventEntity<TEntity>类的定义

复制代码 代码如下:

public interface IEntityEvent<TEntity>
    {
        //变更的实体类对象
        TEntity[] Entities
        {
            get;
        }

        //操作类型
        EntityEventType Type
        {
            get;
        }
    }

    public enum EntityEventType : int
    {
        Create = 0,
        Update = 1,
        Removed = 2
    }

复制代码 代码如下:

[SessionState(SessionStateBehavior.ReadOnly)]
    public class EntityEventController : Controller
    {
        //异步获取对ImageSet对象操作的变更事件Action，millsecondsTimeout为超时时间。
        public async Task<ActionResult> ImageSet(int millisecondsTimeout = 10000)
        {
            return await this.EventAsync<ImageSetData>(millisecondsTimeout);
        }

        private async Task<ActionResult> EventAsync<TEntity>(int millisecondsTimeout)
        {
            IEntityEvent<TEntity> entityEvent = await EntityEventSubcriber.Instance.WaitForEntityEvent<TEntity>(millisecondsTimeout);

            return this.Json(new
            {
                HasEvent = null != entityEvent,
                EntityEvent = entityEvent

            }, JsonRequestBehavior.AllowGet);
        }
    }

(2) 如果Controller层面应用或者Filter中操作过Session，那么为了避免长链接时不会导至同一Session在其他调用中Session Block的情况，需要在Controller头上加入[SessionState(SessionStateBehavior.ReadOnly)] 的Attribute，来表示当前Controller对Session为只读操作，这样就其他操作就不会被阻塞了。

3.这里就不具体写EntityEventSubscriber消息订阅器的代码了，以后将在“消息订阅与发布”的文章中详细描述。

4.jQuery AJAX客户端代码

复制代码 代码如下:

$(document).ready(function () {

        var $hoverList = $("#imageSets").hoverList({title:"图片集列表", selectedIndex: 1 });

        var getEvent = function(){

            var getPattern = "/EasyshirtBackend/imageSet/0";

            $.getJSON("/EasyshirtBackend/event/imageSet/100000" , function(data){

                if(data.HasEvent){

                    //Create
                    if(data.EntityEvent.Type == 0){

                        $.each(data.EntityEvent.Entities, function(i, entity){

                //TODO: 处理实体类新增

                            if(i == data.EntityEvent.Entities.length - 1){

                                getEvent();
                            }
                        });

                        return;
                    }

                    //Update
                    if(data.EntityEvent.Type == 1){

                        $.each(data.EntityEvent.Entities, function(i, entity){

                            //TODO: 处理实体类更新

                            if(i == data.EntityEvent.Entities.length - 1){

                                getEvent();
                            }
                        });

                        return;
                    }

                    //Delete
                    if(data.EntityEvent.Type == 2){

                        $.each(data.EntityEvent.Entities, function(i, entity){

                            //TODO: 处理实体类删除

                            if(i == data.EntityEvent.Entities.length - 1){

                                getEvent();
                            }
                        });
                    }

                }else{

                    $("#imageSets").hoverList("add", data);
                    getEvent();
                }
            });
        };

        getEvent();
    });