IAsyncActionWithProgress<TProgress> IAsyncActionWithProgress<TProgress> IAsyncActionWithProgress<TProgress> IAsyncActionWithProgress<TProgress> Interface

Represents an asynchronous action that can report progress updates to callers. This is the return type for all Windows Runtime asynchronous methods that don't have a result object, but do report progress to callback listeners.

Syntax

Declaration

public interface IAsyncActionWithProgress<TProgress>public interface IAsyncActionWithProgress<TProgress>Public Interface IAsyncActionWithProgress<TProgress>

Inheritance Hierarchy

Remarks

IAsyncActionWithProgress<TProgress> is the return type for all Windows Runtime asynchronous methods that don't communicate a result object, but do enable an app to check the progress of the action. There aren't nearly as many of these as there are methods that use IAsyncAction. IAsyncAction APIs don't report progress and don't have a result.

When you use methods that return IAsyncActionWithProgress<TProgress> in your app code, you usually don't access the IAsyncAction 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 void. 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 IAsyncActionWithProgress<TProgress> 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 with onProgress syntax. .NET has the AsTask extension methods, and once the IAsyncActionWithProgress<TProgress> is converted to a Task, it's easier to cancel, get notification on completion, use IProgress<T>, and so on. For C++/CX, you can wrap the calls using the Concurrency runtime (and use create_task). In other words, IAsyncActionWithProgress<TProgress> 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.

Specifically, if you want to handle progress in .NET code, use the AsTask signature that in an extension usage has a single IProgress reference parameter. (In this usage, the progress unit is already constrained and matches the IAsyncActionWithProgress<TProgress> method you're using.) Provide an object that implements IProgress, and your Report method implementation is invoked each time the Windows Runtime method reports a progress notification.

To monitor the progress of the action (if not using the language-specific techniques described above), set the Progress property, providing it the name of a method that implements the AsyncActionProgressHandler delegate.

Interface inheritance

IAsyncActionWithProgress<TProgress> inherits @Windows.Foundation.IAsyncInfo.Types that implement IAsyncActionWithProgress<TProgress> 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 IAsyncActionWithProgress<TProgress> directly. If writing code using .NET, your method can return a Task. 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 summary

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

Gets or sets the callback method that receives progress notification.

Methods summary

Returns the results of the action.

Properties

  • Completed
    Completed
    Completed
    Completed

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

    public AsyncActionWithProgressCompletedHandler<TProgress> Completed { get; set; }public AsyncActionWithProgressCompletedHandler<TProgress> Completed { get; set; }Public ReadWrite Property Completed As AsyncActionWithProgressCompletedHandler<TProgress>

    Property Value

    • The method that handles the notification.

    Remarks

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

    Generally, a completed IAsyncActionWithProgress<TProgress> method called using language-specific awaitable syntax does nothing further than to return null when it completes.

    If you're implementing IAsyncActionWithProgress<TProgress>, 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.

  • Progress
    Progress
    Progress
    Progress

    Gets or sets the callback method that receives progress notification.

    public AsyncActionProgressHandler<TProgress> Progress { get; set; }public AsyncActionProgressHandler<TProgress> Progress { get; set; }Public ReadWrite Property Progress As AsyncActionProgressHandler<TProgress>

    Property Value

    • A reference to the callback method that handles progress notifications. Implement the AsyncActionProgressHandler delegate to define your callback. TProgress defines the progress unit type, which varies by method implementation.

Methods

Device family

Windows 10 (introduced v10.0.10240.0)

API contract

Windows.Foundation.FoundationContract (introduced v1)

Attributes

Windows.Foundation.Metadata.ContractVersionAttribute
Windows.Foundation.Metadata.GuidAttribute

Details

Assembly

Windows.Foundation.dll