ASP中的观察者.网络代表

本文关键字：网络 观察者 ASP | 更新日期: 2023-09-27 18:06:08

嗯，我在asp.net 3.5网站工作。

我已经像这样设置了一个观察者:

public delegate void ActionNotification();
protected Dictionary<string, List<ActionNotification>> Observers
{
    get
    {
        Dictionary<string, List<ActionNotification>> _observers = Session["Observers"] as Dictionary<string, List<ActionNotification>>;
        if (_observers == null)
        {
            _observers = new Dictionary<string, List<ActionNotification>>();
            Observers = _observers;
        }
        return _observers;
    }
    set
    {
        Session["Observers"] = value;
    }
}
public void Attach(string actionName, ActionNotification observer)
{
    if (!Observers.ContainsKey(actionName))
    {
        Observers.Add(actionName, new List<ActionNotification>());
    }
    Observers[actionName].Add(observer);
}
public void Detach(string actionName, ActionNotification observer)
{
    if (Observers.ContainsKey(actionName))
    {
        Observers[actionName].Remove(observer);
    }
}
public void DetachAll(string actionName)
{
    if (Observers.ContainsKey(actionName))
    {
        Observers.Remove(actionName);
    }
}
public void Notify(string action)
{
    if (Observers.ContainsKey(action))
    {
        foreach (ActionNotification o in Observers[action])
        {
            o.Invoke();
        }
    }
}

我这样使用观察者:

//Esta es llamada al notify con cierto action       
protected void btnNext_Click(object sender, ImageClickEventArgs e)          
{           
    Notify("Next");         
} 
//Y este es el register del Listener            
Attach("Next", new ActionNotification(NextButton_Click));

如果在o.Invoke();例如，我将页面标题更改为"Hello"。在"NextButton_Click"里面，我把它设置为"Goodbye"，在NextButton_Click完成后，标题又回到了"Hello"…

知道为什么吗?

ASP中的观察者.网络代表

我认为问题是您的NextButton_Click事件中的"Page"与您将标题设置为"Hello"的页面不相同。由于在引发事件时正在会话中传递事件，因此它所作用的对象不再在作用域中。你可以用下面的代码重新创建它(它使用了eventhandler，但它们基本上与你在代码中概述的相同)

protected void Page_Load(object sender, EventArgs e)
{
    this.Page.Title = "test";
    //Store it in your session...seems like a weird thing to do given how your page should be stateless, so I would think about what you are
    //trying to do a bit more carefully.  You don't want to call an event handler such as test below from another page in your asp.net app.
    Dictionary<string, EventHandler> myEvents = null;
    if (Session["Invokers"] == null)
    {
        myEvents = new Dictionary<string, EventHandler>();
        Session["Invokers"] = myEvents;
    }
    else
    {
        myEvents = Session["Invokers"] as Dictionary<string, EventHandler>;
    }
    //If the event handler key is not in there then add it
    if (myEvents.ContainsKey("buttonClickOnPageDefault") == false)
    {
        //Subscribe to event (i.e. add your method to the invokation list
        this.TestEvent += new EventHandler(test);
        myEvents.Add("buttonClickOnPageDefault", this.TestEvent);
    }
    else
    {
        //if it does contain this key then you may already be subscribed to event, so unsubscribe in case and then resubscribe...you could
        //probably do this more elegantly by looking at the vales in the GetInvokationList method on the eventHandler
        //Wire up the event
        this.TestEvent -= new EventHandler(test);
        this.TestEvent += new EventHandler(test);
    }
    //Resave the dictionary.
    Session["Invokers"] = myEvents;
}
void test(object o, EventArgs e)
{
    this.Page.Title = "testEvent";
}
public event EventHandler TestEvent;
protected void Button1_Click(object sender, EventArgs e)
{
    if (Session["Invokers"] != null)
    {
        Dictionary<string, EventHandler> myEvents = (Dictionary<string, EventHandler>)Session["Invokers"];
        if (myEvents.ContainsKey("buttonClickOnPageDefault"))
        {
            EventHandler ev = myEvents["buttonClickOnPageDefault"];
            ev(null, EventArgs.Empty);
        }
    }
}

如果你把上面的代码放在一个asp.net页面，它将永远不会改变页面标题，但如果你把一个断点在Test方法，你会看到它被击中。原因是它在不同的页面中被击中(并且该页超出了作用域，并且可能不会被垃圾收集，因为您的事件仍然有对它的引用，因此这可能导致内存泄漏……小心点!)真的，您可能不应该以这种方式使用事件(至少不要在页面上行动……也许它对领域对象有一些实用程序)。请注意，以下操作将起作用(因为它作用于同一页面)

protected void Page_Load(object sender, EventArgs e)
{
    this.Page.Title = "test";
    //Store it in your session...seems like a weird thing to do given how your page should be stateless, so I would think about what you are
    //trying to do a bit more carefully.  You don't want to call an event handler such as test below from another page in your asp.net app.
    this.TestEvent += new EventHandler(test);
    Session["Invoker"] = this.TestEvent;
}
void test(object o, EventArgs e)
{
    this.Page.Title = "testEvent";
}
public event EventHandler TestEvent;
protected void Button1_Click(object sender, EventArgs e)
{
    if (Session["Invoker"] != null)
    {
        EventHandler ev = (EventHandler)Session["Invoker"];
        ev(null, EventArgs.Empty);
    }
}

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