Question

so I have a class request that has a method call that makes an http request

in my main class, when the user presses a button, an isntance of the class req is made and the method call makes the http request is invoked.

I want to have a certain way to know when the call is done so that I can update my textblock with the results

I tried to put that in the button click event handler method:

        req.call(textBox1.Text);
        Dispatcher.BeginInvoke(() =>
        {
            //req is the class instance, outputMessage is the string holds 
            //the result of the http request
            //resultTextBlock is the one I wanna update with the result
            while (req.outputMessage == "none") ;
            resultTextBlock.Text = req.outputMessage;
        });

in the button click event handler, but then the app goes into infinite loop and never finishes, the http request takes fraction of a second to be made if that’s matter

I want to be able to update the resultTextBlock whenever the result is grabbed.

Answer 1

You want a callback from the request once it is completed. This is supported i.e. by the WebClient:

using (WebClient wc = new WebClient())
{
    wc.DownloadStringAsync(new Uri("http://stackoverflow.com"), null);
    wc.DownloadStringCompleted += (s, e) =>
    {
        string outputMessage = e.Result;
        Dispatcher.BeginInvoke(() =>
        {
                resultTextBlock.Text = outputMessage;

        });
    };
}

Edit:

You could pass in a delegate to your req class that you pass the result string (also note the naming guidelines, should be all Uppercase), so change the method signature as follows:

public void Call(string url, Action<string> notifyCompletion)
{

 //once completed:
  notifyCompletion(result);
}

And change the calling code to:

Req myRequest = new Req();
myRequest.Call(textBox1.Text, s => 
{
   Dispatcher.BeginInvoke(() =>
   {
       resultTextBlock.Text = outputMessage;
   });
});