第二个 BeginInvoke 调用声明已完成。为什么？
我反复使用 BeginInvoke 调用一个方法。每次调用后，我都会调用 EndInvoke。
问题在于，对于第二次调用，返回的 IAsyncResult 中的 IsCompleted 成员在 BeginInvoke 调用后立即设置为 true。
这会导致故障，因为程序随后认为第二次调用已完成。
为什么要这样做，以及如何检测第二次调用何时真正完成？
Declarations:
IAsyncResult ar;
Mercury.J4000.Ui.frmMain.doPrintsDelegate printCallback;
The BeginInvoke call:
ar = printCallback.BeginInvoke (jobNameArray, copies, distances, null, null);
The EndInvoke call (in another method):
printCallback.EndInvoke(ar);
I'm repeatedly calling a method with BeginInvoke. After each call, I call EndInvoke.
The problem is that for the second call, the IsCompleted member in the returned IAsyncResult is set to true IMMEDIATELY after the BeginInvoke call.
This causes a malfunction, because the program then thinks the second call is done.
Why does it do this, and how can I detect when the 2nd call is REALLY completed?
Declarations:
IAsyncResult ar;
Mercury.J4000.Ui.frmMain.doPrintsDelegate printCallback;
The BeginInvoke call:
ar = printCallback.BeginInvoke (jobNameArray, copies, distances, null, null);
The EndInvoke call (in another method):
printCallback.EndInvoke(ar);
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我假设您正在做这样的事情：
如果第一个异步操作在第二个异步操作开始之前尚未完成，那么您将丢失
IAsyncResult值。它被第二次调用覆盖。无论如何，您必须跟踪各个
IAsyncResult引用并将它们与您进行的调用关联起来。如果只有一两个变量，您可以轻松跟踪单个变量或集合（通常是List或数组）。这个问题可能会帮助您：我可以使用委托的单个实例来启动多个异步请求吗？
我还建议您考虑对异步委托使用回调。这样，正确的
IAsyncResult将作为参数传递给回调，并且不会出现歧义。但是，使用AsyncCallback可能需要对代码进行重大重构。I assume you're doing something like this:
If the first async operation isn't finished before the second one starts, then you're going to lose the
IAsyncResultvalue. It's overwritten by the second call.Somehow, you have to keep track of the individual
IAsyncResultreferences and associate them with the calls that you made. If you only have one or two, you can easily keep track with individual variables, or a collection (Listor array, typically).This question might help you out: Can I use a single instance of a delegate to start multiple Asynchronous Requests?
I also suggest that you consider using callbacks for your asynchronous delegates. That way, the proper
IAsyncResultis passed as a parameter to the callback, and there's no chance for ambiguity. Using anAsyncCallback, however, might require major refactoring of your code.我的猜测是您在两次调用中使用相同的“ar”变量，因为您已将其声明为字段。每个调用都应该有自己的实例；将该字段声明为
List并编写必要的管道来初始化它并将每个结果与每个调用相关联。您没有为我们提供足够的代码来帮助您完成该部分（事实上，这个答案是一个猜测，因为您没有提供足够的代码。）My guess is that you are using the same "ar" variable in both calls because you have declared it as a field. Each call should have its own instance; declare the field as
List<IAsyncResult>instead and write the requisite plumbing to initialize it and correlate each result with each call. You haven't given enough code for us to help you with that part (in fact this answer is a guess because you haven't given enough code.)