Async/Await implementation of WebBrowser class for .NET

Question

Longtime reader, first-time poster here.

My goal: To be able to take advantage of async/await while using the WebBrowser class. As the WebBrowser.Navigate(string ur

Answer 1

I created this class today, with the help of another post on stackoverflow, I want to get the ready webbrowser control without any thread blocking using (Async/Await).

Dim bb = New wbBrowser
Dim wb = Await bb.GetBrowserAsync("http://www.msn.com")

Here is the class:

Imports System.Threading
Imports System.Threading.Tasks

Public Class wbBrowser
    Implements IDisposable

    Dim m_wbBrowser As New WebBrowser
    Dim m_tcs As TaskCompletionSource(Of WebBrowser)

    Public Sub New()
        m_wbBrowser.ScrollBarsEnabled = False
        m_wbBrowser.ScriptErrorsSuppressed = False
        AddHandler m_wbBrowser.DocumentCompleted, Sub(s, args) m_tcs.SetResult(m_wbBrowser)
    End Sub

    Public Async Function GetBrowserAsync(ByVal URL As String) As Task(Of WebBrowser)
        m_wbBrowser.Navigate(URL)
        Return Await WhenDocumentCompleted(m_wbBrowser)
    End Function

    Private Function WhenDocumentCompleted(browser As WebBrowser) As Task(Of WebBrowser)
        m_tcs = New TaskCompletionSource(Of WebBrowser)
        Return m_tcs.Task
    End Function

    Private disposedValue As Boolean
    Protected Overridable Sub Dispose(disposing As Boolean)
        If Not Me.disposedValue Then
            If disposing Then
                m_wbBrowser.Dispose()
            End If
        End If
        Me.disposedValue = True
    End Sub
    Public Sub Dispose() Implements IDisposable.Dispose
        Dispose(True)
        GC.SuppressFinalize(Me)
    End Sub

End Class

Answer 2

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

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.

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() { ... }
}

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.

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?

Answer 3

You can use TaskCompletionSource<T> to create a Task and mark it as completed later.

I don't see any alternative for the non-generic task, but as Task<T> derives from Task, you could just use a TaskCompletionSource<object> and set the result to null.

Answer 4

I translated Vaibhav's VB code to C#. it's an amazing solution, I don't know why you are disappoint on it.

public class YourClassThatIsUsingWebBrowser : IDisposable
{
    private WebBrowser browser;

    private TaskCompletionSource<BrowserResult> tcs;

    public YourClassThatIsUsingWebBrowser()
    {
        this.browser.DocumentCompleted += AsyncBrowser_DocumentCompleted;

        this.browser.Document.Window.Error += (errorSender, errorEvent) =>
        {
            SetResult(BrowserResult.Exception, errorEvent.Description);
        };
        this.browser.PreviewKeyDown += Browser_PreviewKeyDown;
        this.browser.Navigating += Browser_Navigating;
    }

    private void Browser_Navigating(object sender, WebBrowserNavigatingEventArgs e)
    {
        tcs = new TaskCompletionSource<BrowserResult>();
    }

    private void Browser_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
    {
        if (e.KeyCode == Keys.Escape)
        {
            this.browser.Stop();
            SetResult(BrowserResult.Cancelled);
        }
    }

    private void AsyncBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
    {
        SetResult();
    }


    public async Task<BrowserResult> NavigateAsync(string urlString)
    {
        this.browser.Navigate(urlString);

        return await tcs.Task;
    }

    private void SetResult(BrowserResult result = BrowserResult.Succeed, string error = null)
    {
        if (tcs == null)
        {
            return;
        }
        switch (result)
        {
            case BrowserResult.Cancelled:
                {
                    tcs.SetCanceled();
                    break;
                }
            case BrowserResult.Exception:
                {
                    tcs.SetException(new Exception(error));
                    break;
                }
            case BrowserResult.Succeed:
            default:
                {
                    tcs.SetResult(result);
                    break;
                }
        }

    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    bool disposed = false;
    protected void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                this.browser.Dispose();
            }
        }
        disposed = true;
    }
}
public enum BrowserResult
{
    Succeed,
    Cancelled,
    Exception,
}