在 UI 线程上创建和启动任务 [英] Creating and starting a task on the UI thread

问题描述

当在工作线程上调用的方法需要在 UI 线程上运行代码并等待它完成后再做其他事情时，可以这样做:

When a method that gets called on a worker thread needs to run code on the UI thread and wait for it to complete before doing something else, it can be done like this:

    public int RunOnUi(Func<int> f)
    {
        int res = Application.Current.Dispatcher.Invoke(f);

        return res;
    }

但是如果我想用任务来做呢?RunOnUi 方法有没有办法创建一个在 UI 上启动的任务并返回它，以便调用者(在工作线程上运行)可以等待它?符合以下签名的内容:public TaskStartOnUi(Func f) ?

But what if I wanted to do it with tasks? Is there a way for the RunOnUi method to create a task that is started on the UI and return it so that the caller (which runs on a worker thread) can wait for it? Something that will fit the following signature: public Task<int> StartOnUi(Func<int> f) ?

一种方法如下:

public Task<int> RunOnUi(Func<int> f)
{
    var task = new Task<int>(f);
    task.Start(_scheduler);

    return task;
}

这里，假设 _schduler 持有 ui TaskScheduler.但是我不太习惯创建冷"任务并使用 start 方法来运行它们.这是推荐"的方式还是有更优雅的方式来做到这一点?

Here, assume that _schduler holds the ui TaskScheduler. But I am not too comfortable with creating "cold" tasks and using the start method to run them. Is that the "recommended" way or is there a more elegant way to do it?

推荐答案

只需使用 InvokeAsync 而不是 Invoke 然后返回 Task 在 DispatcherOperation 函数返回.

Just use InvokeAsync instead of Invoke then return the Task<int> inside the DispatcherOperation<int> the function returns.

//Coding conventions say async functions should end with the word Async.
public Task<int> RunOnUiAsync(Func<int> f)
{
    var dispatcherOperation = Application.Current.Dispatcher.InvokeAsync(f);
    return dispatcherOperation.Task;
}

如果您无法访问 .NET 4.5，那就有点复杂了.您将需要使用 BeginInvoke 和 TaskCompletionSource 包装 BeginInvoke 返回的noreferrer">DispaterOperation

If you do not have access to .NET 4.5 it is a little more complicated. You will need to use BeginInvoke and a TaskCompletionSource to wrap the DispaterOperation that BeginInvoke returns

    public Task<int> RunOnUi(Func<int> f)
    {
        var operation = Application.Current.Dispatcher.BeginInvoke(f);
        var tcs = new TaskCompletionSource<int>();
        operation.Aborted += (sender, args) => tcs.TrySetException(new SomeExecptionHere());
        operation.Completed += (sender, args) => tcs.TrySetResult((int)operation.Result);

        //The operation may have already finished and this check accounts for 
        //the race condition where neither of the events will ever be called
        //because the events where raised before you subscribed.
        var status = operation.Status;
        if (status == DispatcherOperationStatus.Completed)
        {
            tcs.TrySetResult((int)operation.Result);
        }
        else if (status == DispatcherOperationStatus.Aborted)
        {
            tcs.TrySetException(new SomeExecptionHere());
        }

        return tcs.Task;
    }

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