| -api-id | -api-type |
|---|---|
T:Windows.Foundation.IAsyncOperation`1 |
winrt interface |
Represents an asynchronous operation, which returns a result upon completion. This is the return type for many Windows Runtime asynchronous methods that have results but don't report progress.
IAsyncOperation<TResult> is the return type for many Windows Runtime asynchronous methods that have a result upon completion, but don't report progress. This constitutes over 650 different Windows Runtime APIs. APIs that do report progress (and have a result) use another interface, IAsyncOperationWithProgress<TResult,TProgress>.
When you use methods that return IAsyncOperation<TResult> (with a TResult specific constraint) in your app code, you usually don't access the IAsyncOperation return value directly. That's because you almost always use the language-specific awaitable syntax. In this case, the apparent return value of the method is the type provided as the TResult parameter. For more info, see Asynchronous programming, or one of the language-specific guides to Windows Runtime asynchronous programming (Call asynchronous APIs in C# or Visual Basic, C++, JavaScript).
It's not common to use IAsyncOperation<TResult> directly even if you don't use a language-specific awaitable syntax. Each of the languages has extension points that are generally easier to use than the Windows Runtime interface. JavaScript has WinJS.Promise, and the then/done syntax. .NET has the AsTask extension method, and once the IAsyncOperation<TResult> is converted to a Task<TResult>, it's easier to get the result, cancel, get notification on completion, and so on. For C++/CX, you can wrap the calls using the Concurrency runtime (and use create_task). In other words, IAsyncOperation<TResult> can be considered runtime-level infrastructure, which each of the languages use as a framework to support awaitable syntax or asynchronous programming models in their own way.
Instead of using IAsyncOperation<TResult>, some Windows Runtime asynchronous methods use custom operation types. For example, DataReaderLoadOperation is a Windows Runtime type that implements IAsyncOperation using uint as the result type. The DataReaderLoadOperation type is then used as the custom operation/result type for the DataReader.LoadAsync method.
IAsyncOperation<TResult> inherits IAsyncInfo. Types that implement IAsyncOperation<TResult> also implement the interface members of IAsyncInfo:
As with calling the existing methods, there are language-specific ways to define asynchronous methods that don't use IAsyncOperation<TResult> directly. If writing code using .NET, your method can return a Task<TResult>. For C++/CX, you can use the Concurrency runtime. However, if you're defining a component, you can use Task/task internally but you must return one of the Windows Runtime interfaces for your public methods. The language-specific asynchronous support types (and many other language-specific types you might conventionally use in code) can't be used for the public surface area of a Windows Runtime component.
IAsyncInfo, IAsyncOperationWithProgress<TResult,TProgress>, IAsyncAction, Task<TResult> (.NET), Asynchronous programming