这是一个包含六种方法的小工具箱，可用于将事件转换为任务：
/// <summary>Converts a .NET event, conforming to the standard .NET event pattern
/// based on <see cref="EventHandler"/>, to a Task.</summary>
public static Task EventToAsync(
Action<EventHandler> addHandler,
Action<EventHandler> removeHandler)
{
var tcs = new TaskCompletionSource<object>();
addHandler(Handler);
return tcs.Task;
void Handler(object sender, EventArgs e)
{
removeHandler(Handler);
tcs.SetResult(null);
}
}
/// <summary>Converts a .NET event, conforming to the standard .NET event pattern
/// based on <see cref="EventHandler{TEventArgs}"/>, to a Task.</summary>
public static Task<TEventArgs> EventToAsync<TEventArgs>(
Action<EventHandler<TEventArgs>> addHandler,
Action<EventHandler<TEventArgs>> removeHandler)
{
var tcs = new TaskCompletionSource<TEventArgs>();
addHandler(Handler);
return tcs.Task;
void Handler(object sender, TEventArgs e)
{
removeHandler(Handler);
tcs.SetResult(e);
}
}
/// <summary>Converts a .NET event, conforming to the standard .NET event pattern
/// based on a supplied event delegate type, to a Task.</summary>
public static Task<TEventArgs> EventToAsync<TDelegate, TEventArgs>(
Action<TDelegate> addHandler, Action<TDelegate> removeHandler)
{
var tcs = new TaskCompletionSource<TEventArgs>();
TDelegate handler = default;
Action<object, TEventArgs> genericHandler = (sender, e) =>
{
removeHandler(handler);
tcs.SetResult(e);
};
handler = (TDelegate)(object)genericHandler.GetType().GetMethod("Invoke")
.CreateDelegate(typeof(TDelegate), genericHandler);
addHandler(handler);
return tcs.Task;
}
/// <summary>Converts a named .NET event, conforming to the standard .NET event
/// pattern based on <see cref="EventHandler"/>, to a Task.</summary>
public static Task EventToAsync(object target, string eventName)
{
var type = target.GetType();
var eventInfo = type.GetEvent(eventName);
if (eventInfo == null) throw new InvalidOperationException("Event not found.");
var tcs = new TaskCompletionSource<object>();
EventHandler handler = default;
handler = new EventHandler((sender, e) =>
{
eventInfo.RemoveEventHandler(target, handler);
tcs.SetResult(null);
});
eventInfo.AddEventHandler(target, handler);
return tcs.Task;
}
/// <summary>Converts a named .NET event, conforming to the standard .NET event
/// pattern based on <see cref="EventHandler{TEventArgs}"/>, to a Task.</summary>
public static Task<TEventArgs> EventToAsync<TEventArgs>(
object target, string eventName)
{
var type = target.GetType();
var eventInfo = type.GetEvent(eventName);
if (eventInfo == null) throw new InvalidOperationException("Event not found.");
var tcs = new TaskCompletionSource<TEventArgs>();
EventHandler<TEventArgs> handler = default;
handler = new EventHandler<TEventArgs>((sender, e) =>
{
eventInfo.RemoveEventHandler(target, handler);
tcs.SetResult(e);
});
eventInfo.AddEventHandler(target, handler);
return tcs.Task;
}
/// <summary>Converts a generic Action-based .NET event to a Task.</summary>
public static Task<TArgument> EventActionToAsync<TArgument>(
Action<Action<TArgument>> addHandler,
Action<Action<TArgument>> removeHandler)
{
var tcs = new TaskCompletionSource<TArgument>();
addHandler(Handler);
return tcs.Task;
void Handler(TArgument arg)
{
removeHandler(Handler);
tcs.SetResult(arg);
}
}
所有这些方法都在创建一个Task将在下一次调用相关事件时完成。此任务永远不会出错或取消，它只能成功完成。
标准事件 ( ) 的使用示例Progress<T>.ProgressChanged：
var p = new Progress<int>();
//...
int result = await EventToAsync<int>(
h => p.ProgressChanged += h, h => p.ProgressChanged -= h);
// ...or...
int result = await EventToAsync<EventHandler<int>, int>(
h => p.ProgressChanged += h, h => p.ProgressChanged -= h);
// ...or...
int result = await EventToAsync<int>(p, "ProgressChanged");
非标准事件的使用示例：
public static event Action<int> MyEvent;
//...
int result = await EventActionToAsync<int>(h => MyEvent += h, h => MyEvent -= h);
任务完成后取消订阅该事件。在此之前没有提供退订机制。