blocks|key|149944|text|避免使用async+void。让你的方法返回Task而不是void。然后你就可以await它们了。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|149945|如下所示：|149946|private+async+Task+RequestToSendOutputReport(List<byte[]>+byteArrays)
{
++++foreach+(byte[]+b+in+byteArrays)
++++{
++++++++while+(condition)
++++++++{
++++++++++++//+we'll+typically+execute+this+code+many+times+until+the+condition+is+no+longer+met
++++++++++++Task+t+=+SendOutputReportViaInterruptTransfer();
++++++++++++await+t;
++++++++}

++++++++//+read+some+data+from+device;+we+need+to+wait+for+this+to+return
++++++++await+RequestToGetInputReport();
++++}
}

private+async+Task+RequestToGetInputReport()
{
++++//+lots+of+code+prior+to+this
++++int+bytesRead+=+await+GetInputReportViaInterruptTransfer();
}|code-block|syntax|javascript|149947|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/system.threading.tasks.task(v=vs.110).aspx|1|https://msdn.microsoft.com/en-GB/library/hh156528.aspx^0|4|A|M|4|T|4|14|5|M|4|0|14|5|1|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]|$9|18|A|19|1|1A]]|E|$]]|$1|F|3|G|5|6|7|1B|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

Avoid <code>async void</code>. Have your methods return <a href="https://msdn.microsoft.com/en-us/library/system.threading.tasks.task(v=vs.110).aspx"><code>Task</code></a> instead of <code>void</code>. Then you can <a href="https://msdn.microsoft.com/en-GB/library/hh156528.aspx"><code>await</code></a> them.

Like this:

<pre><code>private async Task RequestToSendOutputReport(List&lt;byte[]&gt; byteArrays)
{
 foreach (byte[] b in byteArrays)
 {
 while (condition)
 {
 // we'll typically execute this code many times until the condition is no longer met
 Task t = SendOutputReportViaInterruptTransfer();
 await t;
 }

 // read some data from device; we need to wait for this to return
 await RequestToGetInputReport();
 }
}

private async Task RequestToGetInputReport()
{
 // lots of code prior to this
 int bytesRead = await GetInputReportViaInterruptTransfer();
}
</code></pre>

blocks|key|149981|text|下面的代码片段显示了一种确保等待的方法在返回调用方之前完成的方法。然而，我不认为这是一个很好的实践。如果你有不同的想法，请修改我的答案并解释。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|149982|public+async+Task+AnAsyncMethodThatCompletes()
{
++++await+SomeAsyncMethod();
++++DoSomeMoreStuff();
++++await+Task.Factory.StartNew(()+=>+{+});+//+<--+This+line+here,+at+the+end
}

await+AnAsyncMethodThatCompletes();
Console.WriteLine("AnAsyncMethodThatCompletes()+completed.")|code-block|syntax|javascript|149983|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The following snippet shows a way to ensure the awaited method completes before returning to the caller. HOWEVER, I wouldn't say it's good practice. Please edit my answer with explanations if you think otherwise.

<pre><code>public async Task AnAsyncMethodThatCompletes()
{
 await SomeAsyncMethod();
 DoSomeMoreStuff();
 await Task.Factory.StartNew(() =&gt; { }); // &lt;-- This line here, at the end
}

await AnAsyncMethodThatCompletes();
Console.WriteLine("AnAsyncMethodThatCompletes() completed.")
</code></pre>

blocks|key|368371|text|等待AsynMethod完成任务的最佳解决方案是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|368372|var+result+=+Task.Run(async()+=>+await+yourAsyncMethod()).Result;|code-block|syntax|javascript|368373|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Best Solution to wait AsynMethod till complete the task is 

<pre><code>var result = Task.Run(async() =&gt; await yourAsyncMethod()).Result;
</code></pre>

blocks|key|150043|text|实际上，我发现这对返回IAsyncAction的函数更有帮助。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|150044|++++++++++++var+task+=+asyncFunction();
++++++++++++while+(task.Status+==+AsyncStatus.Completed)+;|code-block|syntax|javascript|150045|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Actually I found this more helpful for functions that return IAsyncAction.

<pre><code> var task = asyncFunction();
 while (task.Status == AsyncStatus.Completed) ;
</code></pre>

blocks|key|150075|text|只需让Wait()等待，直到任务完成|type|unstyled|depth|inlineStyleRanges|entityRanges|data|150076|GetInputReportViaInterruptTransfer().Wait();|offset|length|style|CODE|150077|entityMap^0|0|0|18|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

just put Wait() to wait until task completed

<code>GetInputReportViaInterruptTransfer().Wait();</code>

blocks|key|368457|text|以上所有的答案都是正确的，你永远不应该同步等待一个任务……除非你迫不得已！有时，您希望在不受控制的接口实现中调用异步方法，并且没有办法做到“一直向下异步”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|368458|下面是一个至少包含损坏的小类：|368459|public+class+RunSynchronous
{
++++public+static+void+Do(Func<Task>+func)+=>+Task.Run(func).GetAwaiter().GetResult();
++++public+static+T+Do<T>(Func<Task<T>>+func)+=>+Task.Run(func).GetAwaiter().GetResult();
++++public+static+void+Do(Func<ValueTask>+func)+=>+Do(()+=>+func().AsTask());
++++public+static+T+Do<T>(Func<ValueTask<T>>+func)+=>+Do(()+=>+func().AsTask());
}|code-block|syntax|javascript|368460|这个类使用.GetAwaiter.GetResult模式将异步转换为同步。但是如果你在WPF或绑定到特定线程的另一个SynchronizationContext中自己做这件事，你就会死锁。此代码通过将异步操作转移到未与特定线程同步的线程池来避免死锁。只要你不发疯，阻塞所有的线程池线程，你就应该没问题。|368461|用法是这样的|368462|++++return+RunSynchronous.Do(()=>AsyncOperation(a,b,c));|368463|将在线程池上启动AsynchronousOperation(a，b，c)，并等待它返回。只要不显式地同步回原始线程，就应该没问题。|368464|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|X|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

All of the above answers are right, you should never synchronously wait on a task ... unless you have to! Sometimes you want to call an async method inside of a interface implementation you do not control and there is no way to do &quot;async all the way down.&quot;
Here is a little class to at least contain the damage:
<pre><code>public class RunSynchronous
{
 public static void Do(Func&lt;Task&gt; func) =&gt; Task.Run(func).GetAwaiter().GetResult();
 public static T Do&lt;T&gt;(Func&lt;Task&lt;T&gt;&gt; func) =&gt; Task.Run(func).GetAwaiter().GetResult();
 public static void Do(Func&lt;ValueTask&gt; func) =&gt; Do(() =&gt; func().AsTask());
 public static T Do&lt;T&gt;(Func&lt;ValueTask&lt;T&gt;&gt; func) =&gt; Do(() =&gt; func().AsTask());
}
</code></pre>
This class uses the .GetAwaiter.GetResult pattern to actually convert async to sync. But if you do that byitself in WPF or another SynchronizationContext bound to a particular thread you deadlock. This code avoids deadlock by transferring the async operation to the threadpool which is not synchronized to a particular thread. As long as you do not go crazy and block all the threadpool threads you ought to be OK.
usage is like this
<pre class="lang-cs prettyprint-override"><code> return RunSynchronous.Do(()=&gt;AsyncOperation(a,b,c));
</code></pre>
will launch AsynchronousOperation(a,b,c) on the threadpool and wait for it to return. As long as you do not explicitly synchornize back to the origin thread you ought to be OK.

I'm writing a WinForms application that transfers data to a USB HID class device. My application uses the excellent Generic HID library v6.0 which can be found <a href="http://janaxelson.com/hidpage.htm#MyExampleCode" rel="noreferrer">here</a>. In a nutshell, when I need to write data to the device, this is the code that gets called:

<pre><code>private async void RequestToSendOutputReport(List&lt;byte[]&gt; byteArrays)
{
 foreach (byte[] b in byteArrays)
 {
 while (condition)
 {
 // we'll typically execute this code many times until the condition is no longer met
 Task t = SendOutputReportViaInterruptTransfer();
 await t;
 }

 // read some data from device; we need to wait for this to return
 RequestToGetInputReport();
 }
}
</code></pre>

When my code drops out of the while loop, I need to read some data from the device. However, the device isn't able to respond right away so I need to wait for this call to return before I continue. As it currently exists, RequestToGetInputReport() is declared like this:

<pre><code>private async void RequestToGetInputReport()
{
 // lots of code prior to this
 int bytesRead = await GetInputReportViaInterruptTransfer();
}
</code></pre>

For what it's worth, the declaration for GetInputReportViaInterruptTransfer() looks like this:

<pre><code>internal async Task&lt;int&gt; GetInputReportViaInterruptTransfer()
</code></pre>

Unfortunately, I'm not very familiar with the workings of the new async/await technologies in .NET 4.5. I did a little reading earlier about the await keyword and that gave me the impression that the call to GetInputReportViaInterruptTransfer() inside of RequestToGetInputReport() would wait (and maybe it does?) but it doesn't seem like the call to RequestToGetInputReport() itself is waiting because I seem to be re-entering the while loop almost immediately?

Can anyone clarify the behavior that I'm seeing?

How to wait for async method to complete?

我正在编写一个将数据传输到USB类设备的WinForms应用程序。我的应用程序使用了优秀的通用HID库v6.0，它可以在中找到。简而言之，当我需要向设备写入数据时，会调用以下代码：private async void RequestToSendOutputReport(List<byte[]> byteArrays){...

问如何等待异步方法完成？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何等待异步方法完成？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何等待异步方法完成？
EN