Asynchronous Programming in Windows Store App

Introduction

To work with Asynchronous programming we use the await keyword, and also the "Async" keyword. We call the asynchronous APIs in response to a user's action, such as when the user presses the button etc. In this article I explain how to perform asynchronous programming.

In this article I use an example in which, when I click on the button, it fetches the RSS Feed using the syndication class. This feed includes all the latest articles and their published date of any website; in this example I fetch the RSS feed from the http://www.dotnetheaven.com/ site. The asynchronous method SyndicationClient.RetrieveFeedAsync is used to fetch or download the feed.

To work with it use the following steps.

Step 1

First open Visual Studio 2012 RC in Windows 8. Then click File -> New -> Project. Then select Window Store from Visual C#, and select a blank page in the center tab then give the name of the application and then click ok.

Step 2

Add XAML code to MainPage.xaml as in the following:

<Page

x:Class="acron.MainPage"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

xmlns:local="using:acron"

xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

mc:Ignorable="d">

<Grid>

<Grid.Background>

</LinearGradientBrush>

</Grid.Background>

</StackPanel>

<ListView.Background>

</LinearGradientBrush>

</ListView.Background>

<ListView.ItemTemplate>

</StackPanel>

</DataTemplate>

</ListView.ItemTemplate>

</ListView>

</StackPanel>

</Grid>

</Page>

Step 3

Right-click on the project in the Solution Explorer to add a class and choose the class from the window that appears and give a name for the class as you want and then click ok.

Step 4

Add the following code in this class:

namespace acron

{

public class feeddata

{

private List<items> items1=new List<items>();

public List<items> items

{

get{

return this.items1;

}

public class items

{

public string Title

{

get;

set;

}

public DateTime Date

{

get;

set;

}

public Uri link

{

get;

set;

}

Step 5

Now add the following namespace in the MainPage.xaml.cs file:

using Windows.Web.Syndication;

Step 6

Now write the following code in the MainPage.xaml.cs file:

namespace acron

{

public sealed partial class MainPage : Page

{

SyndicationFeed feed = new SyndicationFeed();

public MainPage()

{

this.InitializeComponent();

}

private void listitems_SelectionChanged_1(object sender, SelectionChangedEventArgs e)

{

items I = new items();

I.link = feed.Items[listitems.SelectedIndex].Links[0].Uri;

web.Navigate(I.link);

web.Visibility = Visibility.Visible;

}

private async void Button_Click_1(object sender, RoutedEventArgs e)

{

SyndicationClient client = new SyndicationClient();

client.BypassCacheOnRetrieve = true;

Uri feedUri = new Uri("http://www.dotnetheaven.com/rss/latestarticles.aspx");

feed = await client.RetrieveFeedAsync(feedUri);

feeddata feeddata = new feeddata();

items feeditem = null;

foreach (SyndicationItem item in feed.Items)

{

feeditem = new items();

feeditem.Title = item.Title.Text;

feeditem.Date = item.PublishedDate.DateTime;

feeditem.link = new Uri("http://www.dotnetheaven.com");

feeddata.items.Add(feeditem);

}

listitems.DataContext = feeddata.items;

}

Step 7

Now Press F5 to run the application. The Screen is displayed with the load button and a simple message. When I click on the button, all the latest feed URLs will be fetched from the site and displayed in the listbox as in:

When I click any of these links the specified article will be opened in the Web View as:

Summary

In this article I explained how to use the await keyword to perform asynchronous programming.