c# – ReactiveUI命令并发(WebClient)

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我正在使用RxUI 8的最新预发行版,但我认为这将在以前的版本中发生.

我在我的WPF应用程序中定义了这个ReactiveCommand：

GetWebsiteCommand = ReactiveCommand.CreateFromTask(DownloadString);

private async Task<string> DownloadString()
{
    using (var client = new WebClient())
    {
        return await client.DownloadStringTaskAsync("http://www.google.es");
    }
}

执行该命令时,将引发以下异常：

System.InvalidOperationException’ at System.Reactive.Core.dll: The
calling thread cannot access this object because a different thread
owns it

为什么会这样？我没有创建任何新线程！

这是堆栈跟踪：

System.InvalidOperationException’ at System.Reactive.Core.dll: The
calling thread cannot access this object because a different thread
owns it

 at System.Windows.Threading.Dispatcher.VerifyAccess()
   at System.Windows.DependencyObject.GetValue(DependencyProperty dp)
   at System.Windows.Controls.Primitives.ButtonBase.get_Command()
   at System.Windows.Controls.Primitives.ButtonBase.UpdateCanExecute()
   at System.Windows.Controls.Primitives.ButtonBase.OnCanExecuteChanged(Object sender, EventArgs e)
   at System.Windows.Input.CanExecuteChangedEventManager.HandlerSink.OnCanExecuteChanged(Object sender, EventArgs e)
   at ReactiveUI.ReactiveCommand.OnCanExecuteChanged()
   at ReactiveUI.ReactiveCommand`2.<.ctor>b__9_5(Boolean _)
   at System.Reactive.AnonymousSafeObserver`1.OnNext(T value)
   at System.Reactive.Linq.ObservableImpl.RefCount`1._.OnNext(TSource value)
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive(Int32 count)
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive()
   at System.Reactive.Subjects.ReplaySubject`1.ReplayBase.OnNext(T value)
   at System.Reactive.Subjects.ReplaySubject`1.OnNext(T value)
   at System.Reactive.Linq.ObservableImpl.AsObservable`1._.OnNext(TSource value)
   at System.Reactive.Linq.ObservableImpl.DistinctUntilChanged`2._.OnNext(TSource value)
   at System.Reactive.Linq.ObservableImpl.CombineLatest`3._.S.OnNext(TSecond value)
   at System.Reactive.Linq.ObservableImpl.RefCount`1._.OnNext(TSource value)
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive(Int32 count)
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive()
   at System.Reactive.Subjects.ReplaySubject`1.ReplayBase.OnNext(T value)
   at System.Reactive.Subjects.ReplaySubject`1.OnNext(T value)
   at System.Reactive.Linq.ObservableImpl.AsObservable`1._.OnNext(TSource value)
   at System.Reactive.Linq.ObservableImpl.DistinctUntilChanged`2._.OnNext(TSource value)
   at System.Reactive.Linq.ObservableImpl.Concat`1._.OnNext(TSource value)
   at System.Reactive.Linq.ObservableImpl.Select`2._.OnNext(TSource value)
   at System.Reactive.SafeObserver`1.OnNext(TSource value)
   at System.Reactive.ScheduledObserver`1.Dispatch(ICancelable cancel)
   at System.Reactive.Concurrency.Scheduler.<>c.<ScheduleLongRunning>b__72_0(Action`1 a, ICancelable c)
   at System.Reactive.Concurrency.DefaultScheduler.LongRunning.<>c__DisplayClass1_0`1.<ScheduleLongRunning>b__0(Object arg)
   at System.Reactive.Concurrency.ConcurrencyAbstractionLayerImpl.<>c__DisplayClass7_0.<StartThread>b__0()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

解决方法:

通过堆栈跟踪判断,您将canExecute管道传递给命令.对于您提供的任何管道,您有责任确保它在正确的线程上打勾.如果它在后台线程上打勾,则命令CanExecute事件将在同一个线程上打勾,因此UI将尝试从错误的线程更新关联Button上的IsEnabled属性.

因此,您可能需要针对canExecute管道添加ObserveOn调用.

更新：回答here.

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