Programming WPF, 2nd Edition

Data Source Providers

So far, we've been dealing with simple, hardcoded objects. However, objects can come from long operations for which we'd prefer not to wait, like over a network connection or as translated from XML or relational data. For these cases, we'd really like a layer of indirection for pulling objects from other sources and even pushing that work off to a worker thread if said retrieval is a ponderous operation. For this indirection, we turn to data source providers, whose job is (as the name suggests) to provide data sources for use in binding scenarios.

Object Data Provider

WPF ships with two data source providers, both derived from the DataSourceProvider base class: ObjectDataProvider and XmlDataProvider. Data source providers create a layer of indirection for any kind of operation that produces objects against which to data-bind. For example, if we wanted to load a set of Person objects over the Web, we could encapsulate that logic into a bit of code, as shown in Example 7-29.

Example 7-29. A type to be used by ObjectDataProvider

...
public class Person : INotifyPropertyChanged {...}
public class People : ObservableCollection<Person> {}

public class RemotePeopleLoader {
  // ObjectDataProvider will expose results for binding
  public People LoadPeople(  ) {
    // Load people from afar
    People people = new People(  );
    ...
    return people;
  }
}
...

In Example 7-29, the RemotePeopleLoader class exposes a method (LoadPeople) that will load people however it feels and return that data ...