Monday, May 20, 2013

Quick Tip: Processing HTML Content in Windows Store Apps

The WebView control allows you to display content from sites in your app using a small window that renders the HTML using the same rendering engine as Internet Explorer. It does have some limitations and most likely if you are providing content in your app, your goal is to augment your app with fresh data rather than try to superimpose a full-blown web application on your own native Windows Store app.

Trying to strip down content can be quite cumbersome once you wade through the myriad RegEx expressions or other utilities available. Here’s a simple trick that will work with most content-oriented sites like blogs and online magazines. It allows you to get a more basic view of the content and present it without all of the bells and whistles you may end up pulling down with regular content.

Step 1: Be Mobile

When you are loading content, make the server believe you are mobile. This will often result in a simpler page being presented, often without the heavy script tags or headers, table of contents, and other sections included. Here’s a nice mobile user agent string that will impersonate one of the most popular mobile clients out there, an iPhone:

private const string MobileUserAgent = "Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543a Safari/419.3";

With the mobile header you can override the user agent and request the content. Instead of having the WebView control load the page directly, use the HttpClient and grab the content like this:

var handler = new HttpClientHandler { AllowAutoRedirect = true };

client = new HttpClient(handler);
client.DefaultRequestHeaders.Add("user-agent", MobileUserAgent);
response = await client.GetAsync(new Uri(InsertSuperAwesomeUrlHere));
html = await response.Content.ReadAsStringAsync();

Allowing redirects is important because many pages will auto-detect your mobile client and instead of dynamically serving content will redirect you to a new page for the mobile content. This allows the client to follow the redirect and then pull down the content that is tailored to mobile devices. At this stage you may think you have what you need, but if you pass this to the WebView control you’ll find there is often script content trying to make updates that will throw exceptions and generally cause the WebView to choke. Next you must cleanse the data.

Step 2: Cleanse the Content

Cleansing the content may be easier than you think. It turns out that you need to have clean HTML to share HTML content with other Windows Store apps. In fact, the sharing mechanism provides a nice HtmlFormatHelper class (located in the Windows.ApplicationModel.DataTransfer namespace) designed to package your HTML so it is ready for sharing. It also contains a useful GetStaticFragment method that will strip out the dynamic code so you have nice, clean content. The trick is to prep the HTML as if you were going to share it, then get the static fragment so you have the raw text you can load.

var fragment = HtmlFormatHelper.GetStaticFragment(HtmlFormatHelper.CreateHtmlFormat(html));

Now you are ready to show it to the user.

Step 3: Show it to the User

Now that you have clean HTML, you can ask the WebView control to navigate to the string like this:


That’s all there is to it, and you should get a nice, clean page of data without dynamic tags.

Monday, May 6, 2013

A Fluent Approach to Windows Store Tiles

Windows Store apps have a variety of tricks up their sleeve for engaging the user even when they are not running. Tiles are a perfect example because they provide at-a-glance information to the user from the start screen. Tiles can provide images, text, or a combination of both and support queuing multiple notifications.

Tiles are defined by various pre-built XML templates. The catalog of tiles is available online in the tile template catalog and can be enumerated via TileTemplateType as defined in the Windows.UI.Notifications namespace. The sample apps for Windows 8 from Microsoft include a helper that allows you to create tiles but it requires instantiating specific classes. I wanted to create a more straightforward and fluent method for defining and setting tiles.

It turns out you can get the template for any tile type by calling GetTemplateContent on the TileUpdateManager class with the TileTemplateType you are interested in. Here’s a fast way to get the XmlDocument:

this.xml = TileUpdateManager.GetTemplateContent(templateType);

With the template I can easily inspect how many lines of text and images it is capable of supporting:

this.TextLines = this.xml.GetElementsByTagName("text").Count;
this.Images = this.xml.GetElementsByTagName("image").Count;

Now I can add text and raise an exception if the amount of text the tile can hold is exceeded:

public BaseTile AddText(string text, uint id = 0)
     if (string.IsNullOrWhiteSpace(text))
         throw new ArgumentException("text");
     if (id == 0)
         id = this.textIndex++;
     if (id >= this.TextLines)
         throw new ArgumentOutOfRangeException("id");
     var elements = this.xml.GetElementsByTagName("text");
     var node = elements.Item(id);
     if (node != null)
     return this; }

Notice that the method returns the class instance itself. This sets the class up to support a fluent interface with multiple commands chained together. The same logic is used to add images. When you allow your app to provide both a wide and traditional square tile, you can update both formats with a single call. Therefore, you should be able to merge the definitions of multiple tiles:

public BaseTile WithTile(BaseTile otherTile)
     var otherBinding = this.xml.ImportNode(
     return this; }

Now we can grab the template for a tile, specify text and images, and combine square and rectangular tiles together. The next step is to actually set the tile for the app:

public void Set()

        new TileNotification(this.xml));

I then added an extension method that takes in the type of the tile and returns an instance of my helper class that contains all of the methods described in this post. Putting it all together, the code to set a wide and square tile for an example app I’m building that enumerates all tiles on the system to display the XML looks like this:

// set some default tiles 

                    .AddText("Tile Explorer")
                        .AddText("Tile Explorer")
                        .AddText("A WinRT Example")
                        .AddText("by Jeremy Likness"))

This certainly makes it easier to update tiles. A complete helper will also include similar methods for badges and notifications of course … that’s all part of the work I’m doing. Full source and examples will be available in my upcoming book and I’ll share more details when I have them.