Virtualizing Data in Windows Phone 7: An example

Question

In Windows Phone a ListBox support the virtualization of the data, that means it can only load the data needed and not everything. Peter Torr explains the interface you need to implement.

The short version is that you have to create both a method that return the position of an element and another one that return the element in a specific position. The problem is that the example of Peter Torr is rather dumb, he just return an object with the index as a name.

My question is: how do you actually implement this ?

My idea is to create one file that contains a list of an (integer) index and an (integer) id and a file for every object that contains the actual data. It doesn't seem a really elegant idea, but I can't think of anything better, can you ?

UPDATE

It seems that my question is inaccurate. When I say that the example of Peter Torr is "rather dumb" I am not saying that he has done anything wrong; his objective was simply to explain what interface you need to implement. The practical implementation will depend on the specific data.

What I am asking is what choices do I have to implement this ? Should I simply put the data on a web service and query it every time (with a local cache, of course), build a database, create a file the store the indexes and one for the data ? Is there a solution good enough in every case ? What are the downsides and upsides of every choice ?

Answer 1

The article you linked to includes a link to a downloadable project which demonstrates how to implement this.

Answer 2

What more are you after? The general idea is that the ListBox will call into your IList when it needs data. it will ask for an item at a specific index and you pass back an object. it then, presumably, calls ToString() on that object and displays the result in the list.

What that actual object is and where you pull it from is completely up to you. You might be using a really large array in memory. You might be pulling from IsolatedStorage or a web service. You could certainly use it to pull file info, but I don't suspect anyone has a ready-built IList implementation so that's the part that you will have to implement based on your specific project.