Examples of asynchronous programming for C # async and await

  
 

   
  

  

   
  

  
using System;
   
  

  
using System.Collections.Generic;
   
  

  
using System.Linq;
   
  

  
using System.Text;
   
  

  
using System.Threading.Tasks;
   
  

  
using System.Windows;
   
  

  
using System.Windows.Controls;
   
  

  
using System.Windows.Data;
   
  

  
using System.Windows.Documents;
   
  

  
using System.Windows.Input;
   
  

  
using System.Windows.Media;
   
  

  
using System.Windows.Media.Imaging;
   
  

  
using System.Windows.Navigation;
   
  

  
using System.Windows.Shapes;
   
  

  

   
  

  
// Add a using directive and a reference for System.Net.Http;
   
  

  
using System.Net.Http;
   
  

  

   
  

  
namespace AsyncFirstExample
   
  

  
{
   
  

  
 public partial class MainWindow : Window
   
  

  
 {
   
  

  
 // Mark the event handler with async so you can use await in it.
   
  

  
 private async void StartButton_Click(object sender, RoutedEventArgs e)
   
  

  
 {
   
  

  
 // Call and await separately.
   
  

  
 //Task<int> getLengthTask = AccessTheWebAsync();
   
  

  
 //// You can do independent work here.
   
  

  
 //int contentLength = await getLengthTask;
   
  

  

   
  

  
 int contentLength = await AccessTheWebAsync();
   
  

  

   
  

  
 resultsTextBox.Text +=
   
  

  
 String.Format("\r\nLength of the downloaded string: {0}.\r\n", contentLength);
   
  

  
 }
   
  

  

   
  

  

   
  

  
 // Three things to note in the signature:
   
  

  
 // - The method has an async modifier. 
   
  

  
 // - The return type is Task or Task<T>. (See "Return Types" section.)
   
  

  
 // Here, it is Task<int> because the return statement returns an integer.
   
  

  
 // - The method name ends in "Async."
   
  

  
 async Task<int> AccessTheWebAsync()
   
  

  
 { 
   
  

  
 // You need to add a reference to System.Net.Http to declare client.
   
  

  
 HttpClient client = new HttpClient();
   
  

  

   
  

  
 // GetStringAsync returns a Task<string>. That means that when you await the
   
  

  
 // task you‘ll get a string (urlContents).
   
  

  
 Task<string> getStringTask = client.GetStringAsync("http://msdn.microsoft.com");
   
  

  

   
  

  
 // You can do work here that doesn‘t rely on the string from GetStringAsync.
   
  

  
 DoIndependentWork();
   
  

  

   
  

  
 // The await operator suspends AccessTheWebAsync.
   
  

  
 // - AccessTheWebAsync can‘t continue until getStringTask is complete.
   
  

  
 // - Meanwhile, control returns to the caller of AccessTheWebAsync.
   
  

  
 // - Control resumes here when getStringTask is complete. 
   
  

  
 // - The await operator then retrieves the string result from getStringTask.
   
  

  
 string urlContents = await getStringTask;
   
  

  

   
  

  
 // The return statement specifies an integer result.
   
  

  
 // Any methods that are awaiting AccessTheWebAsync retrieve the length value.
   
  

  
 return urlContents.Length;
   
  

  
 }
   
  

  

   
  

  

   
  

  
 void DoIndependentWork()
   
  

  
 {
   
  

  
 resultsTextBox.Text += "Working . . . . . . .\r\n";
   
  

  
 }
   
  

  
 }
   
  

  
}
   
  

  

   
  

  
// Sample Output:
   
  

  

   
  

  
// Working . . . . . . .
   
  

  

   
  

  
// Length of the downloaded string: 41564.
  
 

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Examples of asynchronous programming for C # async and await