Monday, June 11, 2012

Implementing endless scrolling incremental loading in Metro GridViews and ListViews with ISupportIncrementalLoading

Silverlight & XAML Playground - Metro: Incrementally load GridView and ListView with ISupportIncrementalLoading

"Developers that usually deal with web applications know that one of the pillar of this kind of applications is the use of paged result sets because moving a huge number of records form the server to the browser is not a good idea. Metro applications suffer the same problem. No matter that metro applications are not strictly web applications, the application architecture imply that the connection to a datasource have to be wrapped by web service call so the need of limiting the usage of the network is a strong requirements.

Metro introduces a new interesting method to mange pagine of data. Since the use of a common paging is deprecated by guidelines the requirement is to automatically load records when a user is about to the end of the items available on the user interface. This may be an hard task to do with components like GridView and ListView but thanks to the ISupportIncrementalLoading interface it may be easy like a game.

The ISupportIncrementalLoading interface has to be implemented by a collection. When a GridView detects this interface in the class provided in the ItemsSource property, it automatically change its behavior and works loading items only when they really need to fill empty space because the user reached the end. The definition of the interface is pretty simple:


As a more complex exercise I've prepared an example attached to the end of this post. This example use the incremental strategy to load images from Flickr search API. The application shown in the following screenshot implements the search contract. When a query is made it load a special collection and the items are loaded incrementally when the user scrolls the GridView.


For this purpose I've created a IncrementalSource class. This class implements the ISupportIncrementalLoading interface and is able to manage every data source that exposes a GetPage method. If you have this method already implemented in an application you can easily turn it to incremental loading in a breeze.


I was playing with building a Metro app yesterday and was wondering how I could implement something like this, load a little up front and then load more as the user scrolled... I think this is going to be a key feature for many app's and it's nice to see something like this baked into the Runtime.

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