-event-只能出现在+的左边或= - = [英] -event- can only appear on the left hand side of += or -=

问题描述

我有一个循环的事件。我想，以防止被添加到一个事件相同的方法不止一次。我已经实现了添加和删除访问。

不过，我得到一个错误，指出：

ItemsProcessed只能出现在左手侧+ =或 - =

当我尝试打电话给他们，即使在同一类。

  ItemsProcessed（这一点，新的EventArgs（））; //产生错误
 
公共事件的EventHandler ItemsProcessed 
 {
加
 {
 ItemsProcessed  -  =价值; 
 ItemsProcessed + =价值; 
} 
拆下
 {
 ItemsProcessed  -  =价值; 
} 
} 
  

解决方案

通过一个明确的事件，您需要提供自己的后备存储 - 无论是代表字段或类似 EventHandlerList 。目前的代码是递归的。尝试：

 私人事件处理itemsProcessed; 
公共事件的EventHandler ItemsProcessed 
 {
加
 {
 itemsProcessed- =价值; 
 itemsProcessed + =价值; 
} 
 
拆下
 {
 itemsProcessed- =价值; 
} 
} 
  

然后（并注意到我是一个小的谨慎态度即将开启空边缘的情况下重新穿线）：

  VAR快照= itemsProcessed; 
如果（快照！= NULL）快照（这一点，新的EventArgs（））; 
  

I have an event in a loop. I am trying to prevent the same method being added to an event more than once. I've implemented the add and remove accessors.

However, I get an error stating that:

ItemsProcessed can only appear on the left hand side of += or -=

When I try to call them, even within the same class.

ItemsProcessed(this, new EventArgs()); // Produces error

public event EventHandler ItemsProcessed
{
    add
    {
        ItemsProcessed -= value;
        ItemsProcessed += value;
    }
    remove
    {
        ItemsProcessed -= value;
    }
}

解决方案

With an explicit event, you need to provide your own backing store - either a delegate field or something like EventHandlerList. The current code is recursive. Try:

    private EventHandler itemsProcessed;
    public event EventHandler ItemsProcessed
    {
        add
        {
            itemsProcessed-= value;
            itemsProcessed+= value;
        }

        remove
        {
            itemsProcessed-= value;
        }
    }

Then (and noting I'm being a little cautious about the "about to turn null" edge-case re threading):

    var snapshot = itemsProcessed;
    if(snapshot != null) snapshot (this, new EventArgs());

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