c# - 为什么 Task 实现了 IAsyncResult，但不包含 AsyncWaitHandle 成员？

Question

也许这是个愚蠢的问题。

Task 类是这样声明的:

public class Task : IThreadPoolWorkItem, IAsyncResult, IDisposable

IAsyncResult 接口(interface)声明如下:

public interface IAsyncResult
{
    object AsyncState { get; }
    WaitHandle AsyncWaitHandle { get; }
    bool CompletedSynchronously { get; }
    bool IsCompleted { get; }
}

但是成员AsyncWaitHandle不存在于Task类或实例中。

这段代码:

System.Threading.Tasks.Task t = new System.Threading.Tasks.Task(() => { }); 
t.AsyncWaitHandle.ToString(); 

引发此编译错误:

Error 1 'System.Threading.Tasks.Task' does not contain a definition for 'AsyncWaitHandle' and no extension method 'AsyncWaitHandle' accepting a first argument of type 'System.Threading.Tasks.Task' could be found (are you missing a using directive or an assembly reference?)

然而，这不仅编译:

System.IAsyncResult t = new System.Threading.Tasks.Task(() => { }); 
t.AsyncWaitHandle.ToString(); 

但也有效，因为该成员存在。这是什么魔法？

这是编译器的把戏还是以其他方式隐藏了？

干杯。

Answer 1

Task 显式实现了 IAsyncResult，因此您必须先进行转换:

System.Threading.Tasks.Task t = new System.Threading.Tasks.Task(() => { }); 
((IAsyncResult)t).AsyncWaitHandle.ToString()

显式实现定义如下:

public class Task : IAsyncResult
{
    WaitHandle IAsyncResult.AsyncWaitHandle
    {
        get { ... }
    }
}