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Interface (in Windows.Foundation)
IAsyncAction
IAsyncActionWithProgress
IAsyncOperation
IAsyncOperationWithProgress
Use Case
Use for an async method that produces no results (no arguments
are sent to the completed handler) and reports no progress.
Use for an async method that produces no results but does report
progress, where is the data type of the argument
sent to the progress handler.
Use for an async method that produces results of type
but reports no progress.
Use for an async method that produces results of type
and reports progress with type to a progress
handler.
Having chosen the type of async method we’re creating, we now have to run the method’s code on
another thread. It is possible here to utilize threads directly, using the thread pool exposed in the
Windows.System.Threading API, but there are higher level constructs in both C#/VB and C++ that
make the job much easier.
Async Methods in C#/Visual Basic In C# and Visual Basic we have the
System.Threading.-Tasks.Task class for this purpose. A Task is created through one of the static
Task.Run methods. To this we give an anonymous function (called a delegate in .NET, defined with a
lambda operator =>) that contains the code to execute. To then convert that Task into an appropriate
WinRT async interface, we call the task’s AsAsyncAction or AsAsyncOperation extension method. Here’s
what this looks like in a generic way:
public IAsyncOperation SomeMethodAsync(int id)
{
var task = Task.Run( () => // () => in C# is like function () in JS
{
return "Here is a string.";
});
}
return task.AsAsyncOperation();
If the code inside the task itself performs any asynchronous operations (for which we use the C#
await keyword as described in the blog posts linked earlier), the delegate must be marked with async:
public IAsyncOperation SomeMethodAsync(int id)
{
var task = Task.Run(async () =>
{
var idString = await GetMyStringAsync(id); // await makes an async call looks sync
return idString;
});
}
return task.AsAsyncOperation();
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