我想要一个通用的可重用的代码片段为
wrapping EAP pattern as task,类似于
Task.Factory.FromAsync为
BeginXXX/EndXXX APM pattern.
例如.：
private async void Form1_Load(object sender,EventArgs e)
{
await TaskExt.FromEvent<EventArgs>(
handler => this.webBrowser.DocumentCompleted +=
new WebBrowserDocumentCompletedEventHandler(handler),() => this.webBrowser.Navigate("about:blank"),handler => this.webBrowser.DocumentCompleted -=
new WebBrowserDocumentCompletedEventHandler(handler),CancellationToken.None);
this.webBrowser.Document.InvokeScript("setTimeout",new[] { "document.body.style.backgroundColor = 'yellow'","1" });
}
到目前为止,它看起来像这样：
public static class TaskExt
{
public static async Task<TEventArgs> FromEvent<TEventArgs>(
Action<EventHandler<TEventArgs>> registerEvent,Action action,Action<EventHandler<TEventArgs>> unregisterEvent,CancellationToken token)
{
var tcs = new TaskCompletionSource<TEventArgs>();
EventHandler<TEventArgs> handler = (sender,args) =>
tcs.TrySetResult(args);
registerEvent(handler);
try
{
using (token.Register(() => tcs.SetCanceled()))
{
action();
return await tcs.Task;
}
}
finally
{
unregisterEvent(handler);
}
}
}
是否可以提出类似的东西,但是不需要使用两次WebBrowserDocumentCompletedEventHandler(对于registerEvent / unregisterEvent),而不需要反思？
解决方法
可以使用助手类和流畅的语法：
public static class TaskExt
{
public static EAPTask<TEventArgs,EventHandler<TEventArgs>> FromEvent<TEventArgs>()
{
var tcs = new TaskCompletionSource<TEventArgs>();
var handler = new EventHandler<TEventArgs>((s,e) => tcs.TrySetResult(e));
return new EAPTask<TEventArgs,EventHandler<TEventArgs>>(tcs,handler);
}
}
public sealed class EAPTask<TEventArgs,TEventHandler>
where TEventHandler : class
{
private readonly TaskCompletionSource<TEventArgs> _completionSource;
private readonly TEventHandler _eventHandler;
public EAPTask(
TaskCompletionSource<TEventArgs> completionSource,TEventHandler eventHandler)
{
_completionSource = completionSource;
_eventHandler = eventHandler;
}
public EAPTask<TEventArgs,TOtherEventHandler> WithHandlerConversion<TOtherEventHandler>(
Converter<TEventHandler,TOtherEventHandler> converter)
where TOtherEventHandler : class
{
return new EAPTask<TEventArgs,TOtherEventHandler>(
_completionSource,converter(_eventHandler));
}
public async Task<TEventArgs> Start(
Action<TEventHandler> subscribe,Action<TEventHandler> unsubscribe,CancellationToken cancellationToken)
{
subscribe(_eventHandler);
try
{
using(cancellationToken.Register(() => _completionSource.SetCanceled()))
{
action();
return await _completionSource.Task;
}
}
finally
{
unsubscribe(_eventHandler);
}
}
}
现在你有一个WithHandlerConversion帮助程序,它可以推断转换器参数的type参数,这意味着你只需要一次编写WebBrowserDocumentCompletedEventHandler.
用法：
await TaskExt
.FromEvent<WebBrowserDocumentCompletedEventArgs>()
.WithHandlerConversion(handler => new WebBrowserDocumentCompletedEventHandler(handler))
.Start(
handler => this.webBrowser.DocumentCompleted += handler,() => this.webBrowser.Navigate(@"about:blank"),handler => this.webBrowser.DocumentCompleted -= handler,CancellationToken.None);
