Question

我正在使用TPL进行多功能手术。任务需要向调查组报告进展情况,以便更新进展诊断。由于该表是MVVM,进步方言必须服从于一种名为“进步”的观念模型,该模型以带有签名<编码>的最新进度表的视角模型加以更新。背景任务需要将这种方法称为报告进展情况。

我使用一种方法更新财产,因为它让每一项任务以不同数额增加进步财产。因此,如果我有两个任务,第一个任务需要四倍的时间,第一个任务叫<代码>UpdateProgress(4)/code>,第二个任务叫UpdateProgress(1)。因此,第一个任务完成时进展率为80%,第二个任务完成时进展为100%。

My question is really pretty simple: How do I call the view model method from my background tasks? Code is below. Thanks for your help.

任务使用<代码>Parallel。每种(,在编码中,照此办理:

private void ResequenceFiles(IEnumerable<string> fileList, ProgressDialogViewModel viewModel)
{
    // Wrap token source in a Parallel Options object
    var loopOptions = new ParallelOptions();
    loopOptions.CancellationToken = viewModel.TokenSource.Token;

    // Process images in parallel
    try
    {
        Parallel.ForEach(fileList, loopOptions, sourcePath =>
        {
            var fileName = Path.GetFileName(sourcePath);
            if (fileName == null) throw new ArgumentException("File list contains a bad file path.");
            var destPath = Path.Combine(m_ViewModel.DestFolder, fileName);
            SetImageTimeAttributes(sourcePath, destPath);

            // This statement isn t working
            viewModel.IncrementProgressCounter(1);
        });
    }
    catch (OperationCanceledException)
    {
        viewModel.ProgressMessage = "Image processing cancelled.";
    }
}

The statement viewModel.Increment ProgramressCounter(1) isn thanging an special, but it not take to the main thread. 任务从MVVERSICommand的物体中删除,其编号为:

public void Execute(object parameter)
{
    ...

    // Background Task #2: Resequence files
    var secondTask = firstTask.ContinueWith(t => this.ResequenceFiles(fileList, progressDialogViewModel));

    ...
}

Answer 1

穿甲型肝炎法,可使用异构体异构体。如果你使用卡拉伊伯恩等多国公司框架,则会对派遣者进行抽象的解读,以便你能够使用外阴做几乎相同的事情。 OnUIThread(Action).

微软关于如何使用发送器的文章。

Answer 2

假设你的看法是 constructed(即:根据观点,或针对与观点相关的事件)构造的,几乎总是海事组织,你可以把这一点添加到你建造者身上:

// Add to class:
TaskFactory uiFactory;

public MyViewModel()
{
    // Construct a TaskFactory that uses the UI thread s context
    uiFactory = new TaskFactory(TaskScheduler.FromCurrentSynchronizationContext());
}

接着,当你获得活动时,你可以利用这一机会来挽救:

void Something()
{
    uiFactory.StartNew( () => DoSomething() );
}

Edit: I made an util class. It is static but if you want you can create an interface for it and make it nonstatic:

public static class UiDispatcher
{
    private static SynchronizationContext UiContext { get; set; }

    /// <summary>
    /// This method should be called once on the UI thread to ensure that
    /// the <see cref="UiContext" /> property is initialized.
    /// <para>In a Silverlight application, call this method in the
    /// Application_Startup event handler, after the MainPage is constructed.</para>
    /// <para>In WPF, call this method on the static App() constructor.</para>
    /// </summary>
    public static void Initialize()
    {
        if (UiContext == null)
        {
            UiContext = SynchronizationContext.Current;
        }
    }

    /// <summary>
    /// Invokes an action asynchronously on the UI thread.
    /// </summary>
    /// <param name="action">The action that must be executed.</param>
    public static void InvokeAsync(Action action)
    {
        CheckInitialization();

        UiContext.Post(x => action(), null);
    }

    /// <summary>
    /// Executes an action on the UI thread. If this method is called
    /// from the UI thread, the action is executed immendiately. If the
    /// method is called from another thread, the action will be enqueued
    /// on the UI thread s dispatcher and executed asynchronously.
    /// <para>For additional operations on the UI thread, you can get a
    /// reference to the UI thread s context thanks to the property
    /// <see cref="UiContext" /></para>.
    /// </summary>
    /// <param name="action">The action that will be executed on the UI
    /// thread.</param>
    public static void Invoke(Action action)
    {
        CheckInitialization();

        if (UiContext == SynchronizationContext.Current)
        {
            action();
        }
        else
        {
            InvokeAsync(action);
        }
    }

    private static void CheckInitialization()
    {
        if (UiContext == null) throw new InvalidOperationException("UiDispatcher is not initialized. Invoke Initialize() first.");
    }
}

使用:

void Something()
{
    UiDispatcher.Invoke( () => DoSomething() );
}

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