异步/等待实现web浏览器类的.NET [英] Async/Await implementation of WebBrowser class for .NET

问题描述

隆泰读者，首次海报这里。

Longtime reader, first-time poster here.

我的目标：在使用web浏览器类要能够利用异步优势/等待。由于WebBrowser.Navigate（字符串URL）是一个异步方法，你不能检查HTML文档，直到LoadComplete事件。

My goal: To be able to take advantage of async/await while using the WebBrowser class. As the WebBrowser.Navigate(string url) is an asynchronous method, and you can't examine the html document until the LoadComplete event is fired.

下面是我的（工作）code到目前为止：

Here is my (working) code so far:

public class AsyncWebBrowser
{
    protected WebBrowser m_WebBrowser;

    private ManualResetEvent m_MRE = new ManualResetEvent(false);

    public void SetBrowser(WebBrowser browser) {
        this.m_WebBrowser = browser;
        browser.LoadCompleted += new LoadCompletedEventHandler(WebBrowser_LoadCompleted);
    }

    public Task NavigateAsync(string url) {
        Navigate(url);

        return Task.Factory.StartNew((Action)(() => {
            m_MRE.WaitOne();
            m_MRE.Reset();
        }));
    }

    public void Navigate(string url) {
        m_WebBrowser.Navigate(new Uri(url));
    }

    void WebBrowser_LoadCompleted(object sender, NavigationEventArgs e) {
        m_MRE.Set();
    }
}

这previous类现在允许我使用下列内容：

And this previous class now allows me to use the following:

public async void NavigateToGoogle() {
    await browser.NavigateAsync("www.google.com");
    //Do any necessary actions on google.com
}

不过，我想知道是否有处理这种更高效/有道。具体而言，Task.Factory.CreateNew与阻断ManualResetEvent的。感谢您的输入！

However, I am wondering if there is a more efficient/proper way of handling this. Specifically, the Task.Factory.CreateNew with the blocking ManualResetEvent. Thanks for your input!

推荐答案

首先，我认为这是一个很好的锻炼学习如何异步/等待工作。

First off, I think this is a great exercise for learning how async/await works.

您似乎火圈，以使NavigateAsync返回任务跳跃。但它没有返回一个任务，以便awaitable！是的的方法包含一个计谋的必须返回任务，而是一种方法，它的是awaitable 的需要无法返回任务;所有它做的是回到某种类型的，你可以调用GetAwaiter上。

You seem to be jumping through hoops in order to make NavigateAsync return a Task. But it doesn't have to return a Task in order to be awaitable! A method that contains an await must return Task, but a method that is awaitable need not return Task; all it has to do is return some type that you can call GetAwaiter on.

您可能会考虑实施的小类型是这样的：

You might consider implementing a little type like this:

public struct WebBrowserAwaiter<T>
{
    public bool IsCompleted { get { ... } }
    public void OnCompleted(Action continuation) { ... }
    public T GetResult() { ... }
}

和已经NavigateAsync返回某种类型时，您可以拨打GetAwaiter返回一个WebBrowserAwaiter。没有必要建立一个任务只是为了得到它GetAwaiter方法​​时，你可以使自己的。

and have NavigateAsync return some type upon which you can call GetAwaiter that returns a WebBrowserAwaiter. No need to build up a Task just to get its GetAwaiter method when you can make your own.

更普遍的，有些东西你可能要考虑一下是的如果有就NavigateAsync第二个电话会发生什么，而第一个是依旧导航？的

More generally, something you might want to give some thought to is what happens if there is a second call to NavigateAsync while the first one is still navigating?

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