{"id":109955,"date":"2024-07-04T07:00:00","date_gmt":"2024-07-04T14:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=109955"},"modified":"2024-06-24T09:14:47","modified_gmt":"2024-06-24T16:14:47","slug":"20240604-00-2","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20240704-00\/?p=109955","title":{"rendered":"How do I produce a Windows Runtime asynchronous activity from C#?"},"content":{"rendered":"

Last time, we looked at how to produce a Windows Runtime asynchronous activity in C++\/CX<\/a>. Doing it in C# is similar: The method that converts a C# Task<\/code> to a Windows Runtime asynchronous activity is AsyncInfo.Run<\/code>, and just like PPL’s create_async<\/code>, it infers the resulting asynchronous activity from the signature of the object you pass to it.<\/p>\n

Given a lambda that returns a type R<\/code> and takes the parameters Params...<\/code>, the AsyncInfo.Run<\/code> method returns the following Windows Runtime interface:<\/p>\n\n\n\n\n\n\n
\u00a0<\/th>\nParams…<\/th>\n<\/tr>\n
(Cancellation\u00adToken)<\/code><\/td>\n(Cancellation\u00adToken, IProgress<P>)<\/code><\/td>\n<\/tr>\n
R<\/code> = Task<\/code><\/td>\nIAsyncAction<\/code><\/td>\nIAsyncActionWithProgress<P><\/code><\/td>\n<\/tr>\n
R<\/code> = Task<T><\/code><\/td>\nIAsyncOperation<T><\/code><\/td>\nIAsyncOperationWithProgress<T, P><\/code><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

This is basically the same table that we had for create_async<\/code>, but with three significant changes:<\/p>\n

    \n
  1. The lambda must accept at least a Cancellation\u00adToken<\/code>. (It was optional for create_async<\/code>.)<\/li>\n
  2. The lambda must return a Task<\/code> or Task<T><\/code>. (The create_async<\/code> allowed you to return void<\/code> or T<\/code>.)<\/li>\n
  3. The lambda’s cancellation token and progress reporter parameters are in opposite order!<\/li>\n<\/ol>\n

    As with create_async<\/code>, the lambda can use the IProgress<P&gt<\/code> progress_reporter<P><\/code> to produce progress reports, and the Cancellation\u00adToken<\/code> to detect whether the asynchronous activity has been canceled.<\/p>\n

    Here’s the simplest case: An IAsyncAction<\/code>.<\/p>\n

    Task<Widget> GetWidgetAsync(string id);\r\nTask EnableWidgetAsync(Widget widget, bool enable);\r\n\r\nIAsyncAction EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return AsyncInfo.Run(async (cancel) => {\r\n        var widget = await GetWidgetAsync(id);\r\n        cancel.ThrowIfCancellationRequested();\r\n        await EnableWidgetAsync(widget, enable);\r\n    });\r\n}\r\n<\/pre>\n
    And with progress:<\/p>\n
    IAsyncActionWithProgress<int> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return AsyncInfo.Run(async (CancellationToken cancel,\r\n                                IProgress<int> progress) => {\r\n        progress.Report(0);\r\n        var widget = await GetWidgetAsync(id);\r\n        cancel.ThrowIfCancellationRequested();\r\n        progress.Report(1);\r\n        await EnableWidgetAsync(widget, enable);\r\n    });\r\n}\r\n<\/pre>\n
    The compiler can’t infer what the P<\/code> is for the IProgress<P><\/code> parameter, so you have to specify it explicitly. And then you run into another rule that says that if you provide an explicit type for one lambda parameter, you must do so for all of them, so we’re stuck typing Cancellation\u00adToken<\/code> again.<\/p>\n
    But wait, there’s an easier way: Instead of helping the compiler infer IProgress<P><\/code>, we explicitly specialize the Run<\/code> method.<\/p>\n
    IAsyncActionWithProgress<int> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return AsyncInfo.Run<int><\/span>(async (cancel, progress) => {\r\n        progress.Report(0);\r\n        var widget = await GetWidgetAsync(id);\r\n        cancel.ThrowIfCancellationRequested();\r\n        progress.Report(1);\r\n        await EnableWidgetAsync(widget, enable);\r\n    });\r\n}\r\n<\/pre>\n
    May as well do the async operations, too.<\/p>\n
    IAsyncOperation<bool> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return AsyncInfo.Run(async (cancel) => {\r\n        var widget = await GetWidgetAsync(id);\r\n        cancel.ThrowIfCancellationRequested();\r\n        if (widget == null) return false;       <\/span>\r\n        await EnableWidgetAsync(widget, enable);<\/span>\r\n        return true;                            <\/span>\r\n    });\r\n}\r\n\r\nIAsyncOperationWithProgress<bool, int> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return AsyncInfo.Run<bool, int>(async (cancel, progress) => {\r\n        progress.Report(0);\r\n        var widget = await GetWidgetAsync(id);\r\n        cancel.ThrowIfCancellationRequested();\r\n        progress.Report(1);\r\n        if (widget == null) return false;       <\/span>\r\n        await EnableWidgetAsync(widget, enable);<\/span>\r\n        return true;                            <\/span>\r\n    });\r\n}\r\n<\/pre>\n
    Now, in the case where you don’t support cancellation or progress, you have an alternative: For the case of IAsyncAction<\/code>, you can create a Task<\/code> and then call its AsAsyncAction<\/code> method, and in the case of IAsyncOperation<T><\/code>, you call its its AsAsyncOperation<\/code> method. These aren’t true methods on Task<\/code> but rather extension methods provided by the System.Windows\u00adRuntime\u00adSystem\u00adExtensions<\/code> namespace, so you may need to add a using System.Windows\u00adRuntime\u00adSystem\u00adExtensions;<\/code> to your file.<\/p>\n
    using System.WindowsRuntimeSystemExtensions;\r\n\r\nIAsyncAction EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    Func<Task> taskMaker = async () => {\r\n        var widget = await GetWidgetAsync(id);\r\n        await EnableWidgetAsync(widget, enable);\r\n    };\r\n    return taskMaker().AsAsyncAction();\r\n}\r\n\r\nIAsyncOperation<int> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    Func<Task<int>> taskMaker = async () => {\r\n        var widget = await GetWidgetAsync(id);\r\n        if (widget == null) return false;\r\n        await EnableWidgetAsync(widget, enable);\r\n        return true;\r\n    };\r\n    return taskMaker().AsAsyncOperation();\r\n}\r\n<\/pre>\n
    These conversions are more convenient to use if you just turn the lambda into its own named function:<\/p>\n
    \/\/ IAsyncAction version\r\nasync Task EnableWidgetByIdTaskAsync(string id, bool enable)\r\n{\r\n    var widget = await GetWidgetAsync(id);\r\n    await EnableWidgetAsync(widget, enable);\r\n}\r\n\r\nIAsyncAction EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return EnableWidgetByIdTaskAsync(id, enable).AsAsyncAction();\r\n}\r\n\r\n\/\/ IAsyncOperation version\r\nasync Task<bool> EnableWidgetByIdTaskAsync(string id, bool enable)\r\n{\r\n    var widget = await GetWidgetAsync(id);\r\n    if (widget == null) return false;\r\n    await EnableWidgetAsync(widget, enable);\r\n    return true;\r\n}\r\n\r\nIAsyncOperation<int> EnableWidgetByIdAsync(string id, bool enable)\r\n{\r\n    return EnableWidgetByIdTaskAsync(id, enable).AsAsyncOperation();\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
    The AsyncInfo helper class converts Tasks to Windows Runtime asynchronous activities.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-109955","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
    The AsyncInfo helper class converts Tasks to Windows Runtime asynchronous activities.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109955","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=109955"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109955\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=109955"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=109955"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=109955"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}