[英]WPF Dispatcher.InvokeAsync() strange behavior with async delegate
If you have an async method, like the one below: 如果您有一个异步方法,例如以下方法:
private async Task DoAsync()
{
Console.WriteLine(@"(1.1)");
Thread.Sleep(200);
Console.WriteLine(@"(1.2)");
await Task.Delay(1000);
Console.WriteLine(@"(1.3)");
}
and you call it asynchronously with Dispatcher: 然后使用Dispatcher异步调用它:
Console.WriteLine(@"(1)");
await Application.Current.Dispatcher.InvokeAsync(DoAsync);
Console.WriteLine(@"(2)");
The output you'll get will be: (1) (1.1) (1.2) (2) (1.3) 您将获得的输出将是:(1)(1.1)(1.2)(2)(1.3)
If you use Dispatcher.BeginInvoke() and you'll wait for Completed event, the effect will be the same (which is expected): 如果使用Dispatcher.BeginInvoke()并等待Completed事件,则效果将是相同的(预期):
Console.WriteLine(@"(1)");
var dispatcherOp = Dispatcher.BeginInvoke(new Func<Task>(DoAsync));
dispatcherOp.Completed += (s, args) =>
{
Console.WriteLine(@"(2)");
};
What we see here is that the await in DoAsync() method makes Dispatcher believe the operation ended. 我们在这里看到的是,DoAsync()方法中的await使Dispatcher相信操作已结束。
My question: is it a bug or a feature? 我的问题:是错误还是功能? Do you know any document that describes this behavior?
您是否知道任何描述此行为的文档? I couldn't find anything.
我什么都找不到。
I'm not asking for a workaround. 我不是在寻求解决方法。
It is a bug in your code, the object returned from Application.Current.Dispatcher.InvokeAsync(DoAsync);
这是您代码中的错误,该错误是从
Application.Current.Dispatcher.InvokeAsync(DoAsync);
返回的对象Application.Current.Dispatcher.InvokeAsync(DoAsync);
is a Task<Task>
, you only await the outer task, not waiting for the inner task to complete. 是
Task<Task>
,您仅等待外部任务,而不等待内部任务完成。 These situations is what .Unwrap()
is for. 这些情况就是
.Unwrap()
的用途。
Console.WriteLine(@"(1)");
await Application.Current.Dispatcher.InvokeAsync(DoAsync).Unwrap();
Console.WriteLine(@"(2)");
The output you will get will be: (1) (1.1) (1.2) (1.3) (2) 您将获得的输出将是:(1)(1.1)(1.2)(1.3)(2)
What Unwrap is doing is effectively turning your code in to Unwrap所做的就是有效地将您的代码
Console.WriteLine(@"(1)");
await (await Application.Current.Dispatcher.InvokeAsync(DoAsync));
Console.WriteLine(@"(2)");
But with a nicer looking format. 但具有更好的外观格式。
For documentation see " How to: Unwrap a nested task " 有关文档,请参阅“ 如何:解开嵌套任务 ”
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