Creating an async method in .NET 4.0 that can be used with “await” in .NET 4.5

As others have stated, you start by having a method return Task or Task<TResult>. This is sufficient to await its result in .NET 4.5.

To have your method fit in as well as possible with future asynchronous code, follow the guidelines in the Task-based Asynchronous Pattern document (also available on MSDN). It provides naming conventions and parameter recommendations, e.g., for supporting cancellation.

For the implementation of your method, you have a few choices:

• If you have existing IAsyncResult-based asynchronous methods, use Task.Factory.FromAsync.
• If you have another asynchronous system, use TaskCompletionSource<TResult>.