为异步完成的事件处理程序传递附加变量

发布于 2024-10-04 05:03:42 字数 643 浏览 2 评论 0原文

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{          
    GCService.GeocodeCompleted += new EventHandler<NSpace.GCService.GeocodeCompletedEventArgs>(GeoCode_Method1_GeocodeCompleted);
    GCService.GeocodeAsync(request, waypointIndex);
}

void GeoCode_Method1_GeocodeCompleted(object sender, NSpace.GCService.GeocodeCompletedEventArgs e) 
{
   //***QUESTION: how do I access variable "callinguser" from GeoCode_Method1 in this method??
}

当我调用 GeoCode_Method1 时，我发送“callinguser”字符串变量，并且我想在 GeoCode_Method1_GeocodeCompleted 中访问它（异步 GeoCodingAsync 调用完成时触发）。我该怎么做？

原文

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{          
    GCService.GeocodeCompleted += new EventHandler<NSpace.GCService.GeocodeCompletedEventArgs>(GeoCode_Method1_GeocodeCompleted);
    GCService.GeocodeAsync(request, waypointIndex);
}

void GeoCode_Method1_GeocodeCompleted(object sender, NSpace.GCService.GeocodeCompletedEventArgs e) 
{
   //***QUESTION: how do I access variable "callinguser" from GeoCode_Method1 in this method??
}

When I call into GeoCode_Method1 I send in "callinguser" string variable, and i would like to access this in GeoCode_Method1_GeocodeCompleted (triggered when the async GeoCodingAsync call is done). How do I do this?

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黑寡妇 2024-10-11 05:03:42

最简单的方法是使用 C# lambda 表达式作为事件处理程序。然后，此 lambda 表达式可以调用 GeoCode_Method1_GeocodeCompleted 方法并传递 callinguser 参数。

GCService.GeocodeCompleted += 
  (sender, e) => GeoCode_Method1_GeocodeCompleted(callinguser, sender, e);
GCService.GeocodeAsync(request, waypointIndex); 

void GeoCode_Method1_GeocodeCompleted(
  string callingUser, 
  object sender, 
  Space.GCService.GeocodeCompletedEventArgs e)  { 
     //***QUESTION: how do i access variable "callinguser" from GeoCode_Method1 in this method?? 
}

The easiest way to do this is by using a C# lambda expression as the event handler. This lambda expression can then call into the GeoCode_Method1_GeocodeCompleted method and pass along the callinguser parameter.

GCService.GeocodeCompleted += 
  (sender, e) => GeoCode_Method1_GeocodeCompleted(callinguser, sender, e);
GCService.GeocodeAsync(request, waypointIndex); 

void GeoCode_Method1_GeocodeCompleted(
  string callingUser, 
  object sender, 
  Space.GCService.GeocodeCompletedEventArgs e)  { 
     //***QUESTION: how do i access variable "callinguser" from GeoCode_Method1 in this method?? 
}

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李白 2024-10-11 05:03:42

理想情况下，GCService 有一种方法可以为您处理该问题（如果它正确遵循异步事件模式，则应该如此），但如果没有，则可以使用 C# 闭包的方法，尽管它有点复杂。

您可以按照如下所示进行操作 - 在我的示例中，我展示了如何确保在事件完成时取消订阅 GeocodeCompleted 事件处理程序。

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{    
     // declare the eventHandler before assignment so that it's accessible in the
     // lambda function      
     EventHandler<NSpace.GCService.GeocodeCompletedEventArgs> eventHandler = null;
     eventHandler = (sender, eventArgs) => HandleGeocodeCompleted(sender, eventArgs, callingUser, eventHandler);
     GCService.GeocodeCompleted += eventHandler;
     GCService.GeocodeAsync(request, waypointIndex);
 }

 void HandleGeocodeCompleted(object sender, NSpace.GCService.GeocodeCompletedEventArgs e, string callingUser, EventHandler<NSpace.GCService.GeocodeCompletedEventArgs> eventHandler) 
 {
     GCService.GeocodeCompleted -= eventHandler;
     // use callingUser here
 }

Ideally the GCService would have a way of handling that for you (it should if it properly followed the Async event pattern), but if it doesn't there is a way using C# closures, though it's a little complicated.

You'd do it as shown below - in my sample I've shown how you can make sure that the GeocodeCompleted event handler gets unsubscribed when the event is completed.

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{    
     // declare the eventHandler before assignment so that it's accessible in the
     // lambda function      
     EventHandler<NSpace.GCService.GeocodeCompletedEventArgs> eventHandler = null;
     eventHandler = (sender, eventArgs) => HandleGeocodeCompleted(sender, eventArgs, callingUser, eventHandler);
     GCService.GeocodeCompleted += eventHandler;
     GCService.GeocodeAsync(request, waypointIndex);
 }

 void HandleGeocodeCompleted(object sender, NSpace.GCService.GeocodeCompletedEventArgs e, string callingUser, EventHandler<NSpace.GCService.GeocodeCompletedEventArgs> eventHandler) 
 {
     GCService.GeocodeCompleted -= eventHandler;
     // use callingUser here
 }

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情绪失控 2024-10-11 05:03:42

您应该创建一个 lambda 表达式：

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{          
    GCService.GeocodeCompleted += (sender, e) => {
        MessageBox.Show(callingUser);
    };
    GCService.GeocodeAsync(request, waypointIndex);
}

lambda 表达式可以访问所有外部方法变量和参数。（这称为闭包）

lambda 表达式的 sender 和 e 参数根据其所用作的委托类型隐式类型化。

You should create a lambda expression:

private void GeoCode_Method1(string myaddress, int waypointIndex, string callingUser)
{          
    GCService.GeocodeCompleted += (sender, e) => {
        MessageBox.Show(callingUser);
    };
    GCService.GeocodeAsync(request, waypointIndex);
}

The lambda expression can access all of the outer methods variables and parameters. (This is called a closure)

The lambda expression's sender and e parameters are implicitly typed based on the delegate type it's being used as.

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