可重复使用的模式转换事件到任务 [英] A reusable pattern to convert event into task

问题描述

我想有一个通用的可重复使用的一块$ C $下的包装EAP模式作为任务，类似于<一个东西href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.taskfactory.fromasync%28v=vs.110%29.aspx"相对=nofollow> Task.Factory.FromAsync 做了的 的BeginXXX / EndXXX APM模式。

I'd like to have a generic reusable piece of code for wrapping EAP pattern as task, something similar to what Task.Factory.FromAsync does for 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：

So far, it looks like this:

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);
        }
    }
}

是否可以拿出类似的东西，它仍然会的不可以要求我输入 WebBrowserDocumentCompletedEventHandler 两次（用于 registerEvent / unregisterEvent ），而不是诉诸反射？

Is it possible to come up with something similar, which nevertheless would not require me to type WebBrowserDocumentCompletedEventHandler twice (for registerEvent/unregisterEvent), without resorting to reflection?

推荐答案

这是可能的一个辅助类，并能说一口流利的语法：

It is possible with a helper class and a fluent-like syntax:

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 action,
        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 的辅助方法，它可以从变频器的说法，这意味着你需要编写推断类型参数 WebBrowserDocumentCompletedEventHandler 只有一次。 用法：

Now you have a WithHandlerConversion helper method, which can infer type parameter from converter argument, which means you need to write WebBrowserDocumentCompletedEventHandler only one time. Usage:

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);

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