IAsyncOperation<TResult> IAsyncOperation<TResult> IAsyncOperation<TResult> IAsyncOperation<TResult> Interface

Definition

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.

public : interface IAsyncOperation<TResult> : IAsyncInfo
public interface IAsyncOperation<TResult> : IAsyncInfo
Public Interface IAsyncOperation<TResult> Implements IAsyncInfo
// You can't instantiate an interface directly in JavaScript. You can use objects that implement the interface, however.
Inheritance
IAsyncOperation<TResult>IAsyncOperation<TResult>IAsyncOperation<TResult>IAsyncOperation<TResult>
Attributes
Windows 10 requirements
Device family
Windows 10 (introduced v10.0.10240.0)
API contract
Windows.Foundation.FoundationContract (introduced v1)

Remarks

IAsyncOperation; 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;.

When you use methods that return IAsyncOperation; (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; 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; 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; 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;, 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.

Interface inheritance

IAsyncOperation; inherits IAsyncInfo. Types that implement IAsyncOperation; also implement the interface members of IAsyncInfo:

Notes to implementers

As with calling the existing methods, there are language-specific ways to define asynchronous methods that don't use IAsyncOperation; 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.

Properties

Completed Completed Completed Completed

Gets or sets the method that handles the operation completed notification.

public : AsyncOperationCompletedHandler<TResult> Completed { get; set; }
public AsyncOperationCompletedHandler<TResult> Completed { get; set; }
Public ReadWrite Property Completed As AsyncOperationCompletedHandler<TResult>
var asyncOperationCompletedHandler = iAsyncOperation`1.completed;
iAsyncOperation`1.completed = asyncOperationCompletedHandler;

Remarks

The Windows Runtime enforces that this property can only be set once on an operation.

Generally, a completed IAsyncOperation; method called using awaitable syntax does nothing further than to return its result (an object of the TResult type) when it completes.

If you're implementing IAsyncOperation;, then the set implementation of Completed should store the handler, and the surrounding logic should invoke it when Close is called. The implementation should set the asyncStatus parameter of invoked callbacks appropriately if there is a Cancel call, Status is not Completed, errors occurred, and so on.

See Also

ErrorCode ErrorCode ErrorCode ErrorCode

Inherited from IAsyncInfo

Id Id Id Id

Inherited from IAsyncInfo

Status Status Status Status

Inherited from IAsyncInfo

Methods

Cancel Cancel Cancel Cancel

Inherited from IAsyncInfo

Close Close Close Close

Inherited from IAsyncInfo

GetResults() GetResults() GetResults() GetResults()

Returns the results of the operation.

public : TResult GetResults()
public TResult GetResults()
Public Function GetResults() As TResult
var tResult = iAsyncOperation`1.getResults();
Returns
TResult TResult TResult TResult

The results of the operation.

Remarks

Notes to implementers

Implementers should return the specific value that the operation type should return to callers upon completion. When the method that uses the custom operation type returns, while using an awaitable syntax (the usual usage) this provides the return value of the operation to the method caller.

See Also

See Also