ReactiveUI调用线程无法访问此对象，因为另一个线程拥有它

Question

如果我在后台代码中使用绑定，则在change IsBusy处单击后会出现错误

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

xaml：

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

政务司司长：

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，所有的工作都是这样的：

政务司司长：

DataContext = new TestViewModel();

xaml：

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

为什么会发生这种情况？

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; });
}

或者更好：

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属性的实现方式与此类似：

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

在这种情况下，当您单击按钮时，将在非UI线程上调用RegisterAsyncFunction中的lambda函数。在IsBusy = false指令中，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。

如果在Xaml中将ViewModel绑定到View，则不会调用ViewModel属性。

要修复此代码，应使用Dispatcher.Invoke调用IsBusy = false

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