wpf - 如何对使用 VisualTreeHelper 的东西进行单元测试？

Question

我有这个静态辅助函数：

    public static DependencyObject GetParentObject(DependencyObject child)
    {
        if (child == null) return null;
        ContentElement contentElement = child as ContentElement;

        if (contentElement != null)
        {
            var parent = ContentOperations.GetParent(contentElement);
            if (parent != null) return parent;

            var fce = contentElement as FrameworkContentElement;
            return fce != null ? fce.Parent : null;
        }

        //if it's not a ContentElement, rely on VisualTreeHelper
        return VisualTreeHelper.GetParent(child);
    }

它适用于实际应用程序，但我正在尝试为它编写一些单元测试。这是我的第一次尝试：

    [Test]
    public void GetParentObject_returns_immediate_parent()
    {
        var contentControl = new ContentControl();
        var textBox = new TextBox();

        contentControl.BeginInit();
        contentControl.Content = textBox;
        contentControl.EndInit();

        var result = UIHelper.GetParentObject(textBox);
        Assert.AreSame(contentControl, result);
    }

不幸的是它失败了，因为VisualTreeHelper它返回 null。我如何模拟一个可以工作的可视化树？

score 3 · Accepted Answer

Based on this answer here on printing documents via Wpf-controls and convert to XPS I came up with the following extension method to create the visual tree. It works well within NUnit without STA-thread or anything.

/// <summary>
/// Render a UIElement such that the visual tree is generated, 
/// without actually displaying the UIElement
/// anywhere
/// </summary>
public static void CreateVisualTree(this UIElement element)
{
    var fixedDoc = new FixedDocument();
    var pageContent = new PageContent();
    var fixedPage = new FixedPage();
    fixedPage.Children.Add(element);
    pageContent.ToMaybeOf<IAddChild>().Do(c => c.AddChild(fixedPage));
    fixedDoc.Pages.Add(pageContent);

    var f = new XpsSerializerFactory();
    var w = f.CreateSerializerWriter(new MemoryStream());
    w.Write(fixedDoc);
}

Please note that

the other answer uses an API of the Reach-dll that does not look like the API I am seeing. I assume that there are differences between .NEt Framework versions 3.5 and 4.0
the ToMaybeOf stuff basically means to treat pageContent as IAddChild and do an action on that interface
this will not work with an element of type Window since the element is essentially added as a child to a Visual and Window will complain bitterly about this.

score 2 · Accepted Answer

这就是静力学有问题的原因。

您可以抽象接口背后的功能并创建使用静态方法的默认实现。然后，您可以使用依赖注入，这使得该单元测试变得微不足道——模拟对 IVisualTreeHelper 的依赖或滚动您自己的存根实现，您可以将其配置为返回您分配的任何值。

public class Foo
{
    static IVisualTreeHelper visualTreeHelper;

    static Foo()
    {
        Foo.visualTreeHelper = new FrameworkVisualTreeHelper();
    }

    public Foo(IVisualTreeHelper visualTreeHelper)
    {
        Foo.visualTreeHelper = visualTreeHelper;
    }

    public static DependencyObject GetParentObject(DependencyObject child)
   {
       if (child == null) return null;
       ContentElement contentElement = child as ContentElement;

       if (contentElement != null)
       {
           var parent = ContentOperations.GetParent(contentElement);
           if (parent != null) return parent;

           var fce = contentElement as FrameworkContentElement;
           return fce != null ? fce.Parent : null;
       }

       //if it's not a ContentElement, rely on the IVisualTreeHelper
       return visualTreeHelper.GetParent(child);
   }
}

public interface IVisualTreeHelper
{
    DependencyObject GetParent(DependencyObject reference);
}

public class FrameworkVisualTreeHelper : IVisualTreeHelper
{
    public DependencyObject GetParent(DependencyObject reference)
    {
        return VisualTreeHelper.GetParent(reference);
    }
}

VisualTreeHelper显然，如果您在其他地方使用其他方法，您可能需要将其他方法添加到您的接口和默认实现中。

它仍然不完全干净，因为您正在测试的单元本身是静态的，当您尝试对依赖于 UIHelper 类的静态方法的任何类进行单元测试时，您将遇到完全相同的问题。

score -1 · Accepted Answer

要模拟一个可视化树，您必须实际创建和渲染一个。所以你必须创建一个实际的窗口，这对于单元测试来说并不是特别理想。

wpf - 如何对使用 VisualTreeHelper 的东西进行单元测试？

3 回答 3

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