Calling HttpClient from UI in WinRT - Nothing happens

Question

I'm trying to get the content of a website in a Windows 8 Metro App. I'm still a bit confused about the asyn and wait methods.
But this is what I have:

private void HelloButton_Click(object sender, RoutedEventArgs e)
{  
    GetPage().Wait();
}

private async Task GetPage()
{
      HttpClient client = new HttpClient();

      HttpResponseMessage response = await client.GetAsync("http://www.supertext.ch");
      response.EnsureSuccessStatusCode();
      string responseBody = await response.Content.ReadAsStringAsync();
}

Unfortuantely, nothing happens. If try to debug it, it just stops at GetAsync().
Do I need to make the HelloButton_Click function also async?
Even though I wait for the completion of the function GetPage()?
Can I call network requests directly from the GUI thread?

score 2 · Accepted Answer · answered Nov 14 '12 at 11:29

2

Don't call Wait on the task. await it. This is a common beginners bug.

answered Nov 14 '12 at 11:29

usr

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Ok, wait is just plain wrong? When would it be appropriate to use it? – Remy Nov 14 '12 at 12:55
1

@Remy wait blocks the thread, causing a deadlock. I suggest you search for "await wait deadlock" on Stack Overflow. I'm sure you'll find good material on that topic. For example: http://stackoverflow.com/questions/13140523/await-vs-task-wait-deadlock – usr Nov 14 '12 at 13:28
1

@Remy: It's almost always wrong. `Wait` is a holdover from .NET 4 and is *not* used for `async` code. I have [a blog post that describes this deadlock situation in detail](http://nitoprograms.blogspot.com/2012/07/dont-block-on-async-code.html). – Stephen Cleary Nov 14 '12 at 13:50

score 2 · Answer 2 · answered Nov 14 '12 at 11:54

2

Change HelloButton_Click to :

private async void HelloButton_Click(object sender, RoutedEventArgs e)
{  
    await GetPage();
}

answered Nov 14 '12 at 11:54

Antonio Bakula

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Calling HttpClient from UI in WinRT - Nothing happens

2 Answers2