wpf - ReactiveUI 调用线程无法访问此对象，因为不同的线程拥有它

Question

如果我在后面的代码中使用绑定，单击更改 IsBusy 后会出现错误

"The calling thread cannot access this object because a different thread owns it"

xml:

<Button x:Name="AsyncCommand"
                    Height="20"
                    Content="PushAsync"/>
<ProgressBar x:Name="IsBusy"
              Height="20"/>

CS：

this.Bind(ViewModel, x => x.IsBusy, x => x.IsBusy.IsIndeterminate);
this.BindCommand(ViewModel, x => x.AsyncCommand, x => x.AsyncCommand);

视图模型：

public class TestViewModel : ReactiveObject
    {
        public TestViewModel()
        {
            AsyncCommand = new ReactiveAsyncCommand();
            AsyncCommand
                .RegisterAsyncFunction(x => 
                 { IsBusy = true; Thread.Sleep(3000); return "Ok"; })
                .Subscribe(x => { IsBusy = false; });
        }

        private bool isBusy;

        public bool IsBusy
        {
            get { return isBusy; }
            set { this.RaiseAndSetIfChanged(x => x.IsBusy, ref isBusy, value); }
        }
        public ReactiveAsyncCommand AsyncCommand { get; protected set; }
    }

但是，如果我在 xaml 中进行绑定，则一切正常，如下所示：

CS：

DataContext = new TestViewModel();

xml:

<Button x:Name="AsyncCommand"
                    Height="20"
                    Content="PushAsync"
                    Command="{Binding AsyncCommand}"/>
<ProgressBar x:Name="IsBusy"
              Height="20"
              IsIndeterminate="{Binding IsBusy}"/>

为什么会这样？

Answer 1

试试这个：

public TestViewModel()
{
    AsyncCommand = new ReactiveAsyncCommand();
    AsyncCommand.Subscribe(_ => IsBusy = true);

    AsyncCommand
        .RegisterAsyncFunction(x => 
         { Thread.Sleep(3000); return "Ok"; })
        .Subscribe(x => { IsBusy = false; });
}

甚至更好：

ObservableAsPropertyHelper<bool> _IsBusy;
public bool IsBusy {
    get { return _IsBusy.Value; }
}

public TestViewModel()
{
    AsyncCommand = new ReactiveAsyncCommand();
    AsyncCommand
        .RegisterAsyncFunction(x => 
         { Thread.Sleep(3000); return "Ok"; })
        .Subscribe(x => { /* do a thing */ });

    AsyncCommand.ItemsInFlight
        .Select(x => x > 0 ? true : false)
        .ToProperty(this, x => x.IsBusy);
}

Answer 2

我假设您的 ViewModel 属性的实现与此类似：

public TestViewModel ViewModel
{
    get { return (TestViewModel)DataContext; }
    set { DataContext = value; }
}

在这种情况下，当您单击按钮时，您的 lambda 函数RegisterAsyncFunction会在非 UI 线程上调用。在IsBusy = false指令 ReactiveUI 调用 ViewModel 属性，该属性试图在非 UI 线程上获取 DataContext，这会导致InvalidOperationException.

如果将 ViewModel 绑定到 Xaml 中的 View，则不会调用 ViewModel 属性。

要修复此代码，您应该使用Dispatcher.Invoke来调用IsBusy = false：

AsyncCommand
    .RegisterAsyncFunction(x => 
    {
        Application.Current.Dispatcher.Invoke(() =>IsBusy = true); 
        Thread.Sleep(3000); 
        return "Ok"; 
    })'