使用依赖属性和异步 ctp

Question

我创建了一些示例 ViewModel 来测试使用 asyncCtp 的 DP：

public class SampleVm : DependencyObject
{

    public static readonly DependencyProperty SampleDependencyPropertyProperty =
        DependencyProperty.Register("SampleDependencyProperty", typeof (int), typeof (SampleVm), new PropertyMetadata(default(int)));

    public int SampleDependencyProperty
    {
        get { return (int) GetValue(SampleDependencyPropertyProperty); }
        set { SetValue(SampleDependencyPropertyProperty, value); }
    }
    public ISampleModel _model;
    public SampleVm(ISampleModel model)
    {
        _model = model;
    }

    public async Task SetDependencyProperty()
    {
        var modelData = await TaskEx.Run(() => _model.GetSomeIntegerValue());
        SampleDependencyProperty = modelData;
    }
}

注入到 ViewModel 的模型是：

public interface ISampleModel
{
    int GetSomeIntegerValue();
}

public class SampleModel : ISampleModel
{
    public int GetSomeIntegerValue()
    {
        return 10;
    }
}

当我运行 WPF 应用程序时没有问题，但是当我想用以下代码对其进行测试时：

[Fact]
public async Task CheckValueSetting()
{
    var model = new Mock<ISampleModel>();
    model.Setup(x => x.GetSomeIntegerValue()).Returns(5);
    var viewModel =new SampleVm(model.Object);

    await viewModel.SetDependencyProperty();

    Assert.Equal(5, viewModel.SampleDependencyProperty);
}

我收到以下错误：

System.InvalidOperationException: The calling thread cannot access this object because a different thread owns it.

Server stack trace: 

    at System.Windows.Threading.Dispatcher.VerifyAccess()
    at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
    at WpfApplication4.SampleVm.set_SampleDependencyProperty(Int32 value) in SampleVM.cs: line 19
    at WpfApplication4.SampleVm.<SetDependencyProperty>d__1.MoveNext() in SampleVM.cs: line 30

    Exception rethrown at [0]: 
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
    at WpfApplication4.SampleVmFixture.<CheckValueSetting>d__0.MoveNext() in SampleVmFixture.cs: line 16 

那么解决办法是什么？

Answer 1

首先，我建议您使用Microsoft.Bcl.Async package 升级到VS2012。这将使您能够使用最新工具以 .NET 4.0 为目标。 Async CTP 存在无法修复的已知错误，并且存在安装问题（无法修复），这将使设置新的开发机器变得相当困难。

但在删除 Async CTP 之前，请查看 Async CTP 目录下的 (C# Testing) Unit Testing 目录。你会发现有几种类型可以帮助进行单元测试，例如GeneralThreadAffineContext：

[Fact]
public async Task CheckValueSetting()
{
    var model = new Mock<ISampleModel>();
    model.Setup(x => x.GetSomeIntegerValue()).Returns(5);
    SampleVm viewModel;
    await GeneralThreadAffineContext.Run(async () =>
    {
        viewModel = new SampleVm(model.Object);
        await viewModel.SetDependencyProperty();
    });

    Assert.Equal(5, viewModel.SampleDependencyProperty);
}