async method callback with Task.ContinueWIth?

Question

I have a method that pulls some HTML via the HttpClient like so:

public static HttpClient web = new HttpClient();
public static async Task<string> GetHTMLDataAsync(string url)
{                    
    string responseBodyAsText = "";
    try
    {
       HttpResponseMessage response = await web.GetAsync(url);
       response.EnsureSuccessStatusCode();
       responseBodyAsText = await response.Content.ReadAsStringAsync();
    }
    catch (Exception e)
    {
       // Error handling
    }

    return responseBodyAsText;
}

I have another method that looks like so:

private void HtmlReadComplete(string data)
{
    // do something with the data
}

I would like to be able to call GetHTMLDataAsync and then have it call HtmlReadComplete on the UI thread when the html has been read. I naively thought this could somehow be done with something that looks like

GetHTMLDataAsync(url).ContinueWith(HtmlReadComplete);

But, I can't get the syntax correct, nor am I even sure that's the appropriate way to handle it.

Thanks in advance!

Answer 1

public async void ProcessHTMLData(string url)
{
    string HTMLData = await GetHTMLDataAsync(url);
    HTMLReadComplete(HTMLData);
}

or even

public async void ProcessHTMLData(string url)
{
    HTMLReadComplete(await GetHTMLDataAsync(url));
}

Answer 2

You're close, but ContinueWith() takes a delegate with Task as its parameter, so you can do:

GetHTMLDataAsync(url).ContinueWith(t => HtmlReadComplete(t.Result));

Normally, you should be careful with using Result together with async , because Result blocks if the Task hasn't finished yet. But in this case, you know for sure that the Task is complete, you Result won't block.