How to create a basic RSS reader for Windows Phone 8

项目
05/20/2016

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

You can create a basic RSS reader by completing the following steps. The guidance and code examples presented here are based on a code sample called RSS Reader Sample.

This topic contains the following sections.

Creating a Windows Phone app project

In Visual Studio, create a new Windows Phone App project.

Adding a reference to the Syndication DLL

To use the SyndicationFeed class, you must first add a DLL reference.

To add a reference to the Syndication DLL

In Visual Studio, on the Project menu, select Add Reference, and then select the Browse tab.
Navigate to your Program Files (x86) directory.
Navigate to Microsoft SDKs/Silverlight/v4.0/Libraries/Client/.
Select System.ServiceModel.Syndication.dll, and then click OK.

Note

If you see a prompt at this step that asks if you want to continue, click Yes.

Creating an RSS text trimmer

Description text in an RSS feed can often contain HTML, encoded characters, and other data that you may not want to display in an RSS reader. You can create a class that strips HTML and other unwanted data from description text, and then set up the class as a converter for the XAML field.

To create an RSS text trimmer

In Solution Explorer, right-click the project name, click Add, and then click New Item.
In the Installed Templates pane, select Visual C#, and then in the middle pane select Class.
Name the file RssTextTrimmer.cs, and then click Add.
In Solution Explorer, double-click the RssTextTrimmer.cs file.

Add the following namespaces:

using System.Windows.Data;
using System.Globalization;
using System.Text.RegularExpressions;

Update the class definition so that it implements the IValueConverter interface:
```
public class RssTextTrimmer : IValueConverter
```

Add the following code inside the RssTextTrimmer class:

// Clean up text fields from each SyndicationItem. 
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    if (value == null) return null;

    int maxLength = 200;
    int strLength = 0;
    string fixedString = "";

    // Remove HTML tags and newline characters from the text, and decode HTML encoded characters. 
    // This is a basic method. Additional code would be needed to more thoroughly  
    // remove certain elements, such as embedded Javascript. 

    // Remove HTML tags. 
    fixedString = Regex.Replace(value.ToString(), "<[^>]+>", string.Empty);

    // Remove newline characters.
    fixedString = fixedString.Replace("\r", "").Replace("\n", "");

    // Remove encoded HTML characters.
    fixedString = HttpUtility.HtmlDecode(fixedString);

    strLength = fixedString.ToString().Length;

    // Some feed management tools include an image tag in the Description field of an RSS feed, 
    // so even if the Description field (and thus, the Summary property) is not populated, it could still contain HTML. 
    // Due to this, after we strip tags from the string, we should return null if there is nothing left in the resulting string. 
    if (strLength == 0)
    {
        return null;
    }

    // Truncate the text if it is too long. 
    else if (strLength >= maxLength)
    {
        fixedString = fixedString.Substring(0, maxLength);

        // Unless we take the next step, the string truncation could occur in the middle of a word.
        // Using LastIndexOf we can find the last space character in the string and truncate there. 
        fixedString = fixedString.Substring(0, fixedString.LastIndexOf(" "));
    }

    fixedString += "...";

    return fixedString;
}

// This code sample does not use TwoWay binding, so we do not need to flesh out ConvertBack.  
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    throw new NotImplementedException();
}

Set up the RssTextTrimmer class as a converter by double-clicking App.xaml in Solution Explorer, and then adding the following code inside the <Application.Resources> tag:
```
<converter:RssTextTrimmer xmlns:converter="clr-namespace:namespace" x:Key="RssTextTrimmer" />
```
Where namespace is the name of your project's namespace. For example, in the Basic RSS Reader for Windows Phone 8 sample, namespace is replaced with sdkBasicRSSReaderWP8CS.

Updating the XAML code

To update the XAML code

In Solution Explorer, double-click the MainPage.xaml file.

Replace <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"></Grid> with the following XAML code:

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="0,0,12,0">
    <Button Content="Load Feed" Height="72" HorizontalAlignment="Left" Margin="9,6,0,0" Name="loadFeedButton" VerticalAlignment="Top" Width="273" Click="loadFeedButton_Click" />

    <ListBox Name="feedListBox" Height="468" HorizontalAlignment="Left" Margin="20,100,0,0" VerticalAlignment="Top" Width="444" ScrollViewer.VerticalScrollBarVisibility="Auto" SelectionChanged="feedListBox_SelectionChanged">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <StackPanel VerticalAlignment="Top">
                    <TextBlock TextDecorations="Underline" FontSize="24" Name="feedTitle" TextWrapping="Wrap" Margin="12,0,0,0" HorizontalAlignment="Left" Foreground="{StaticResource PhoneAccentBrush}" Text="{Binding Title.Text, Converter={StaticResource RssTextTrimmer}}" />
                    <TextBlock Name="feedSummary" TextWrapping="Wrap" Margin="12,0,0,0" Text="{Binding Summary.Text, Converter={StaticResource RssTextTrimmer}}" />
                    <TextBlock Name="feedPubDate" Foreground="{StaticResource PhoneSubtleBrush}" Margin="12,0,0,10" Text="{Binding PublishDate.DateTime}" />
                </StackPanel>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
    <Border BorderBrush="{StaticResource PhoneSubtleBrush}" BorderThickness="1" Height="2" HorizontalAlignment="Left" Margin="20,88,0,0" Name="border1" VerticalAlignment="Top" Width="438" />
</Grid>

Updating the code-behind file

To update the code-behind file