What is the difference between Task<> and IAsyncOperation<>

问题

I am writing a metro app.

This works:

    HttpClient client = new HttpClient();
    var bytes = await client.GetByteArrayAsync(new Uri("www.microsoft.com"));

This doesn't:

    var folder = Windows.Storage.ApplicationData.Current.LocalFolder;
    var file = await folder.GetFileAsync("text.txt");

The first one returns a Task<>, the second one return an IAsyncOperation<>

What is the difference? Why are there two different types? How can I fix the second sample?

回答1:

IAsyncOperation is a metro asynchronous operation. You can await an IAsyncOperation.

However, you can't use IAsyncOperation with Task.WhenAll or Task.WhenAny. To use IAsyncOperation instances with these methods, you should call the StartAsTask extension method, as such:

var folder = Windows.Storage.ApplicationData.Current.LocalFolder;
var fileTask = folder.GetFileAsync("text.txt").AsTask();

来源：https://stackoverflow.com/questions/10034239/what-is-the-difference-between-task-and-iasyncoperation