Currently the LoadOnDemandCollection accepts a callback of the following format in the constructor:
public LoadOnDemandCollection(Func<CancellationToken, IEnumerable> action)It is a very common scenario to populate the items asynchronously. In its current form the collection would require blocking the current thread to populate the results:
ItemsSource = new ListViewLoadOnDemandCollection((cancelationToken) =>
{
var result = new List<ItemsModel>();
try
{
var items = dataService.GetItemsAsync().Result;
// TODO: Handle the result.
return result;
}
catch (Exception e)
{
// TODO: Handle the exception.
return null;
}
});This is not desired, as using Task.Result blocks the current thread and is considered an anti-pattern, in general.
A better approach would be to add a second overload of the constructor, allowing asynchronous calls:
public LoadOnDemandCollection(Func<CancellationToken, Task<IEnumerable>> action)This way we can use async and await in the callback instead:
ItemsSource = new ListViewLoadOnDemandCollection(async (cancelationToken) =>
{
var result = new List<ItemsModel>();
try
{
var items = await dataService.GetItemsAsync();
// TODO: Handle the result.
return result;
}
catch (Exception e)
{
// TODO: Handle the exception.
return null;
}
});According to my tests, the first blocking approach is not a problem, as the ListViewLoadOnDemandCollection starts a thread internally. That behavior is not obvious however, and using Task.Result is somewhat counterintuitive, so the second approach is much better from the user's perspective.