如何使用动态参数类型创建委托

本文关键字：创建 类型 参数 何使用 动态 | 更新日期: 2023-09-27 18:34:06

我有一个类型为 EventHandlerpublic static void AssignDelegate(this ICommunicationObject client, string eventName) { EventInfo eventInfo = client.GetType().GetEvent(eventName); EventHandler<AsyncCompletedEventArgs> eventHandler = (object o, AsyncCompletedEventArgs e) => { // Some generic code that will be used as a handler to all events } // I want be able to add the eventHandler to the eventInfo using the // AddEventHandler method, but this does not seem possible since this // event accepts delegates of type EventHandler<SomeClassThatExtendsAsyncCompletedEventArgs> // (It probably would if the EventHandler generic argument was contravariant) eventInfo.AddEventHander(client, eventHandler); }

还有其他方法可以做到这一点吗？也许在运行时更改参数的类型e？

如何使用动态参数类型创建委托

你可以通过反射来做到这一点：

// your global handler, it can be regular method
private static void GlobalEventHandler(object o, AsyncCompletedEventArgs e)
{
    Console.WriteLine(e.GetType());
}
// your extension method
public static void AssignDelegate(this object client, string eventName)
{
    // get event
    EventInfo eventInfo = client.GetType().GetEvent(eventName);
    // get build handler method
    MethodInfo buildHandlerMethod = MethodInfo.GetCurrentMethod().DeclaringType.GetMethod("BuildHandler");
    // get type of arg; 
    // eventInfo.EventHandlerType is EventHandler<T>, where T: AsyncCompletedEventArgs, 
    // so we are interested in T
    Type argType = eventInfo.EventHandlerType.GetGenericArguments()[0];
    // add handler
    eventInfo.AddEventHandler(client, (Delegate)buildHandlerMethod.MakeGenericMethod(argType).Invoke(null, null));
}
// method which returns proper handler for event, 
// it delegates invocation to GlobalEventHandler
public static EventHandler<T> BuildHandler<T>() where T : AsyncCompletedEventArgs
{
    return GlobalEventHandler;
}
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