通过

Async.SwitchToContext 方法 (F#)

  • 项目

创建一个异步计算，该异步计算通过使用同步上下文对象的 Post 方法运行其延续。

命名空间/模块路径：Microsoft.FSharp.Control

程序集：FSharp.Core（在 FSharp.Core.dll 中）

// Signature:
static member SwitchToContext : SynchronizationContext -> Async<unit>

// Usage:
Async.SwitchToContext (syncContext)

参数

返回值

一个使用 syncContext 上下文进行执行的异步计算。

备注

如果 syncContext 为空，则该异步计算与 Async.SwitchToThreadPool 等效。

示例

以下代码示例演示如何使用 Async.SwitchToContext 来切换到 UI 线程以更新 UI。 在此示例中，将更新指示计算完成状态的进程栏。

open System.Windows.Forms

let form = new Form(Text = "Test Form", Width = 400, Height = 400)
let syncContext = System.Threading.SynchronizationContext()
let button1 = new Button(Text = "Start")
let label1 = new Label(Text = "", Height = 200, Width = 200,
                       Top = button1.Height + 10)
form.Controls.AddRange([| button1; label1 |] )

let async1(syncContext, form : System.Windows.Forms.Form) =
    async {
        let label1 = form.Controls.[1]
        // Do something.
        do! Async.Sleep(10000)
        let threadName = System.Threading.Thread.CurrentThread.Name
        let threadNumber = System.Threading.Thread.CurrentThread.ManagedThreadId
        label1.Text <- label1.Text + sprintf "Something [%s] [%d]" threadName threadNumber

        // Switch to the UI thread and update the UI.
        do! Async.SwitchToContext(syncContext)
        let threadName = System.Threading.Thread.CurrentThread.Name
        let threadNumber = System.Threading.Thread.CurrentThread.ManagedThreadId
        label1.Text <- label1.Text + sprintf "Here [%s] [%d]" threadName threadNumber

        // Switch back to the thread pool.
        do! Async.SwitchToThreadPool()
        // Do something.
        do! Async.Sleep(10000)
        let threadName = System.Threading.Thread.CurrentThread.Name
        let threadNumber = System.Threading.Thread.CurrentThread.ManagedThreadId
        label1.Text <- label1.Text +
                       sprintf "Switched to thread pool [%s] [%d]" threadName threadNumber
    }

let buttonClick(sender:obj, args) =
    let button = sender :?> Button
    Async.Start(async1(syncContext, button.Parent :?> Form))
    let threadName = System.Threading.Thread.CurrentThread.Name
    let threadNumber = System.Threading.Thread.CurrentThread.ManagedThreadId
    button.Parent.Text <- sprintf "Started asynchronous workflow [%s] [%d]" threadName threadNumber
    ()

button1.Click.AddHandler(fun sender args -> buttonClick(sender, args))
Application.Run(form)

平台

Windows 8，Windows 7，Windows server 2012中，Windows server 2008 R2

版本信息

F#核心库版本

支持:2.0，4.0，可移植

请参见

参考

Control.Async 类 (F#)

Microsoft.FSharp.Control 命名空间 (F#)