c# - 为什么没有设置 ScrollOwner？

Question

我开发测试驱动并想要测试，我实现 IScrollInfo 的控件是否返回正确的 ScrollViewer。此外，我想测试我的控件是否在 ScrollOwner 上调用了 InvalidateScrollInfo。

控件看起来像:

private class MyControl : UserControl, IScrollInfo
{
    public ScrollViewer ScrollOwner { get; set; }

    ... other code to implement IScrollInfo
}

我的测试(nunit)看起来像:

[Test]
public void Should_be_scrollable()
{
    var ControlToTest = new MyControl();
    var scrollViewer = new ScrollViewer { Content = ControlToTest };
    var window = new Window { Content = scrollViewer };
    window.Show();

    Assert.That(ControlToTest, Is.InstanceOf<IScrollInfo>());
    Assert.That(ControlToTest.ScrollOwner, Is.SameAs(scrollViewer));
}

但不幸的是，Assert.That(ControlToTest.ScrollOwner, Is.SameAs(scrollViewer)); 失败了，因为 ScrollOwner 为 null。

问题 为什么 ControlToTest.ScrollOwner 为空？

我做了什么:我查看了设置 ScrollOwner 的位置。这发生在 ScrollContentPresenter 中的 HookupScrollingComponents 中，后者又在 OnApplyTemplate 中调用。据我了解，在测量元素时会应用模板。这应该在显示窗口时完成。即使我添加 window.Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.Render); 形成:

[Test]
public void Should_be_scrollable()
{
    var scrollViewer = new ScrollViewer { Content = ControlToTest };
    var window = new Window { Content = scrollViewer };
    window.Show();
    window.Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.Render);

    Assert.That(ControlToTest, Is.InstanceOf<IScrollInfo>());
    Assert.That(ControlToTest.ScrollOwner, Is.SameAs(scrollViewer));
}

它没有帮助。 ScrollOwner 仍然是 null。为什么？

奖励问题:如何测试在 scrollViewer 上调用了 InvalidateScrollInfo()？

Answer 1

CanContentScroll 必须设置为 true。

比测试有效:

[Test]
public void Should_be_scrollable()
{
    var ControlToTest = new MyControl();
    var scrollViewer = new ScrollViewer
    {
        Content = ControlToTest,
        CanContentScroll = true
    };
    var window = new Window { Content = scrollViewer };
    window.Show();

    Assert.That(ControlToTest, Is.InstanceOf<IScrollInfo>());
    Assert.That(ControlToTest.ScrollOwner, Is.SameAs(scrollViewer));
}

现在可以使用 ControlToTest.ScrollOwner 进行进一步测试。

奖励问题的答案:当您将 ControlToTest.ViewportHeight 更改为小于测试中的 ControlToTest.ExtentHeight 时，您可以检查 ControlToTest .ScrollOwner.ComputedVerticalScrollBarVisibility 属性断言调用了 ScrollOwner.InvalidateScrollInfo()。这可能看起来像:

var scrollViewer = new ScrollViewer
{
    Content = ControlToTest,
    CanContentScroll = true,
    VerticalScrollBarVisibility = ScrollBarVisibility.Auto
};
var window = new Window { Content = scrollViewer, Height = 600 };
window.Show();
Assert.That(
    ControlToTest.ScrollOwner.ComputedVerticalScrollBarVisibility,
    Is.EqualTo(Visibility.Collapsed));

window.Height = 300;
Render();

Assert.That(
    ControlToTest.ScrollOwner.ComputedVerticalScrollBarVisibility,
    Is.EqualTo(Visibility.Visible));

与

private void Render()
{
    ControlToTest.Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.ContextIdle);
}