在单元测试中使用WPF调度正确的方法 [英] Correct method for using the WPF Dispatcher in unit tests

问题描述

我试图遵循在单元测试中使用WPF调度的建议。为了得到我NUnit测试运行

I am trying to follow the suggestions from Using the WPF Dispatcher in unit tests in order to get my nUnit test to run.

当我写我的单元测试如下，它的工作原理：

When I write my unit test as below, it works:

[Test]
public void Data_Should_Contain_Items()
{
    DispatcherFrame frame = new DispatcherFrame();
        PropertyChangedEventHandler waitForModelHandler = delegate(object sender, PropertyChangedEventArgs e)
        {
          if (e.PropertyName == "Data")
          {
            frame.Continue = false;
          }
        };
    _myViewModel.PropertyChanged += waitForModelHandler;
    Dispatcher.PushFrame(frame);

    Assert.IsTrue(_myViewModel.Data.Count > 0, "Data item counts do not match");
}

不过，如果我尝试使用DispatcherUtil的建议，这不工作方式：

However, if I try to use the suggestion of the DispatcherUtil, it does not work:

[Test]
public void Data_Should_Contain_Items()
{
    DispatcherUtil.DoEvents();
    Assert.IsTrue(_myViewModel.Data.Count > 0, "Data item counts do not match");
}

public static class DispatcherUtil
{
    [SecurityPermissionAttribute(SecurityAction.Demand, Flags = SecurityPermissionFlag.UnmanagedCode)]
    public static void DoEvents()
    {
        DispatcherFrame frame = new DispatcherFrame();
        Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background,
            new DispatcherOperationCallback(ExitFrame), frame);
        Dispatcher.PushFrame(frame);
    }

    private static object ExitFrame(object frame)
    {
        ((DispatcherFrame)frame).Continue = false;
        return null;
    }
}

当我使用的是DispatcherUtil，它看起来像来电ExitFrame发生的太快，之前数据已准备好。

When I am using the DispatcherUtil, it looks like the call to ExitFrame happens too soon, before the data is ready.

我这不是正确使用DispatcherUtil？这似乎是一个更好的方法，用来处理调度而不是等待从视图模型的回调。

Am I not using the DispatcherUtil correctly? It seems like a better method to use to handle the dispatcher rather then waiting for callbacks from the view model.

推荐答案

由于调度在单元测试有问题，我的解决办法是打破调度您的视图模型的依赖。我认为像目前你已经硬编码引用：

Since the dispatcher is problematic in unit tests, my solution would be to break your view-model's dependency on the dispatcher. I assume that currently you have hard coded references like:

Dispatcher.CurrentDispatcher.BeginInvoke(..

调度程序是一个外部的依赖，不应该是你的单元测试的一部分 - 我们可以假设调度作品

The dispatcher is an external dependency and shouldn't be part of your unit tests - we can assume the dispatcher works.

我会使用依赖注入（无论是穷人芒，团结，等等）。
创建一个合适的接口代表调度。
创建一个真正的实现它包装真正的调度员
创建一个使用Action.BeginInvoke
在假你记录所有IAsyncResults返回调用的BeginInvoke假执行。结果
然后有一个辅助方法，这将等待所有调用完成后，你可以在你的测试中使用，以等待完成。

I would use dependency injection (either poor mans, Unity, etc). Create a suitable interface representing the dispatcher. Create a real implementation which wraps the real dispatcher. Create a fake implementation which uses Action.BeginInvoke. In the fake you record all IAsyncResults returned to calls to BeginInvoke.
Then have a helper method which would wait for all calls to completed which you can use in your test to wait for completion.

或者有一个视图模型基类，它做同样的事情。调用调度正常，但可直接调用在测试过程中假的。

Or have a view model base class which does the same thing. Calls the dispatcher normally but can be directed to call a fake during tests.

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